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6.1 General
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This clause describes the mobile originating call procedures for the CS Fallback in EPS.
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6.2 Mobile Originating call in Active Mode - PS HO supported
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This flow may be executed when the eNodeB knows that both the UE and the network support PS HO, in the normal case. Clause 6.6 describes the procedure when the procedure is rejected by the MME.
Figure 6.2-1: CS Call Request in E-UTRAN, Call in GERAN/UTRAN
NOTE 1: DTM is not mandatory for CS Fallback to work and is not linked to PS HO.
1a. The UE sends an Extended Service Request for mobile originating CS fallback to MME. Extended Service Request message is encapsulated in RRC and S1‑AP messages. The UE only transmits this request if it is attached to CS domain (with a combined EPS/IMSI Attach).
1b. The MME sends an S1‑AP UE Context Modification Request (CS Fallback Indicator, LAI) message to eNodeB. This message indicates to the eNodeB that the UE should be moved to UTRAN/GERAN. The registered PLMN for CS domain is identified by the PLMN ID included in the LAI, which is allocated by the MME.
If MME determines the CS Fallback procedure needs priority handling based on MPS CS Priority in the UE's EPS subscription or because the call is an emergency call, it also sets priority indication, i.e. "CSFB High Priority", in the S1AP message to the eNodeB as specified in TS 36.413 [35]. In the case of emergency call, the MME also requests the eNodeB to inhibit roaming and access restrictions via the Additional CS Fallback Indicator as specified in TS 36.413 [35].
1c. The eNodeB shall reply with S1-AP UE Context Modification Response message.
1d. If configured to support the return to the last used PLMN after CSFB, the MME sends a MO CSFB indication via SGs to the MSC in order to indicate that the CM service request message, as described in step 4b in this clause , is due to the CSFB via CS MO call.
2. The eNodeB may optionally solicit a measurement report from the UE to determine the target GERAN/UTRAN cell to which PS handover will be performed.
NOTE: Based on operator policy, the priority indicator received in step1b may be used by eNodeB to decide whether to continue CS Fallback procedures with PS HO, i.e. step3a, or to initiate radio release procedure to redirect the UE to 2G/3G Circuit Switch as specified in clause 6.3.
3a. The eNodeB triggers PS handover to a GERAN/UTRAN neighbour cell by sending a Handover Required message to the MME. The eNodeB selects the target PS handover cell considering the PLMN ID and possibly the LAC for CS domain provided by the MME in step 1b.
If the eNB is a HeNB, the HeNB should perform step 3 through step 6 of clause 6.3 instead of PS HO if the HeNB detects that the UE has only LIPA PDN Connections. CSFB will not be completed successfully when PS HO is performed if the UE has only LIPA PDN Connections as PS HO would result in the MME detaching the UE.
NOTE 2: For details how the HeNodeB determines whether a PDN connection is a LIPA PDN connection see TS 23.401 [2], clause 4.3.16.
In the following an inter-RAT handover from E-UTRAN to UTRAN or GERAN as specified in TS 23.401 [2] begins. The eNodeB indicates in the Source RNC to Target RNC Transparent container that PS handover was triggered due to CSFB. The eNodeB also indicates whether CSFB was triggered for emergency or priority call handling purpose. If the network supports a priority call handling, the eNodeB may forward the priority indication to the target GERAN/UTRAN in the Source to Target Transparent Container, and the target GERAN/UTRAN allocates radio bearer resources taking received priority indication take into account. As part of this handover, the UE receives a HO from E‑UTRAN Command and tries to connect to a cell in the target RAT. The HO from E-UTRAN Command may contain a CS Fallback Indicator which indicates to UE that the handover is triggered due to a CS fallback request. If the HO from E-UTRAN Command contains a CS Fallback Indicator and the UE fails to establish connection to the target RAT, then the UE considers that CS fallback has failed. Service Request procedure is considered to be successfully completed when PS Handover procedure is completed successfully.
NOTE 3: During the PS HO the SGSN does not create a Gs association with the MSC/VLR.
NOTE 4: Service Request procedure supervision timer shall be sufficiently long considering the optional measurement reporting at step 2.
When the UE arrives at the target cell, if the target RAT is UTRAN, the UE establishes the radio signalling connection by sending an RRC Initial Direct Transfer message as specified in TS 25.331 [7] that contains a NAS message. The CN Domain Indicator is set to "CS" in the Initial Direct Transfer message.
If the target RAT is GERAN A/Gb mode: The UE establishes a radio signalling connection by using the procedures specified in TS 44.018 [4] (i.e. UE requests and is assigned a dedicated channel where it sends a SABM containing a NAS message to the BSS and the BSS responds by sending a UA). Upon receiving the SABM (containing the NAS message) the BSS sends a COMPLETE LAYER 3 INFORMATION message (containing the NAS message) to the MSC which indicates CS resources have been allocated in the GERAN cell. If both the UE and the target cell support enhanced CS establishment in DTM (indicated by GERAN system information included within the HO from E‑UTRAN Command) a RR connection may be established while in packet transfer mode without release of the packet resources, see TS 43.055 [24]. After the establishment of the main signalling link as described in TS 44.018 [4] the UE enters either Dual Transfer Mode or Dedicated Mode.
3b. If the target RAT is GERAN and the UE has entered Dedicated Mode, the UE starts the Suspend procedure (see TS 44.018 [4]) unless both the UE and the Target cell support DTM in which case TBF re-establishment may be performed.
3c. A Gn/Gp-SGSN that receives the Suspend message from the UE follows the Suspend procedure specified in TS 23.060 [3], clause 16.2.1.1.1.
An S4-SGSN that receives the Suspend message from the UE follows the Suspend procedure specified in TS 23.060 [3]. The S4-SGSN deactivates GBR bearers towards S-GW and P-GW(s) by initiating MS-and SGSN Initiated Bearer Deactivation procedure as specified in TS 23.060 [3], and starts the preservation and suspension of non-GBR bearers by sending Suspend Notification message to the S-GW. The S-GW releases all RNC related information (address and TEIDs) for the UE if Direct Tunnel is established, and sends Suspend Notification message to the P-GW(s). The SGSN stores in the UE context that UE is in suspended status. All the preserved non-GBR bearers are marked as suspended status in the S-GW and P-GW(s). The P-GW should discard packets if received for the suspended UE.
4a. If the LA of the new cell is different from the one stored in the UE (which is received as part of Combined Attach/TAU procedure in E-UTRAN), the UE shall initiate a Location Area Update procedure as follows:
- if the network is operating in NMO-I (Network Modes of Operation), the UE shall initiate a separate Location Area Update before initiating the RAU procedure instead of a Combined RA/LA Update procedure (to speed up the CSFB procedure); or
- if the network is operating in NMO-II, the UE shall initiate a Location Area Update before initiating the RAU procedure required for PS handover.
When the UE initiates a Location Area Update the UE shall set the "follow-on request" flag in the LAU Request in order to indicate to the MSC not to release the Iu/A connection after the LAU procedure completion. The UE shall indicate to the target MSC that this is an originating call establishment as a result of CSFB by including the "CSMO" flag. Further the UE performs any Routing Area Update procedure as specified by TS 23.060 [3].
The UE may initiate a Location Area Update procedure immediately when the UE is handed over to the target cell i.e. before the UE receives e.g. LAI or NMO information as part of the RAN Mobility Information.
When different from the serving MSC, the target MSC derives the Last Used LTE PLMN from the MAP Send Identification message received from the serving MSC/VLR during the Location Area Update procedure.
4b. The UE sends a CM Service Request to the MSC. The UE shall indicate to the MSC that this is an originating call establishment as a result of CSFB by including the "CSMO" flag.
5. If the UE is not registered in the MSC serving the 2G/3G target cell or the UE is not allowed in the LA, the MSC shall reject the CM service request, if implicit location update is not performed. The CM Service Reject shall trigger the UE to perform a Location Area Update or a Combined RA/LA Update procedure as specified in TS 23.060 [3] for the different Network Modes of Operation (NMO).
When different from the serving MSC, the target MSC derives the Last Used LTE PLMN from the MAP Send Identification message received from the serving MSC/VLR during the Location Area Update procedure.
6. The UE initiates the CS call establishment procedure and the UE shall include the CSMO flag in the CM Service Request to the MSC.
7. The UE performs any remaining steps of the inter-RAT handover from E-UTRAN to UTRAN or GERAN as specified in TS 23.401 [2].
If the UE remains on UTRAN/GERAN after the CS voice call is terminated the UE performs normal mobility management procedures as defined in TS 23.060 [3] and TS 24.008 [21].
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6.3 Mobile Originating call in Active Mode – No PS HO support
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This procedure is executed when PS HO is not supported, in the normal case. Clause 6.6 describes the procedure when the procedure is rejected by the MME.
Figure 6.3-1: CS Call Request in E-UTRAN, Call in GERAN/UTRAN without PS HO
1a. The UE sends an Extended Service Request for mobile originating CS fallback to the MME. Extended Service Request message is encapsulated in RRC and S1‑AP messages. The UE only transmits this request if it is attached to CS domain (with a combined EPS/IMSI Attach).
1b. The MME sends an S1‑AP UE Context Modification Request (CS Fallback Indicator, LAI) message to eNodeB. This message indicates to the eNodeB that the UE should be moved to UTRAN/GERAN. The registered PLMN for CS domain is identified by the PLMN ID included in the LAI, which is allocated by the MME.
If MME determines the CS Fallback procedure needs priority handling based on MPS CS Priority in the UE's EPS subscription or because the call is an emergency call, it sets priority indication, i.e. "CSFB High Priority", in the S1AP message to the eNodeB as specified in TS 36.413 [35]. In the case of emergency call, the MME also requests the eNodeB to inhibit roaming and access restrictions via the Additional CS Fallback Indicator as specified in TS 36.413 [35].
1c. The eNodeB shall reply with S1-AP UE Context Modification Response message.
1d. If configured to support the return to the last used PLMN after CSFB, the MME sends a MO CSFB indication via SGs to the MSC in order to indicate that the CM service request message, as described in step 9 in this clause, is due to the CSFB via CS MO call.
2. The eNodeB may optionally solicit a measurement report from the UE to determine the target GERAN/UTRAN cell to which the redirection procedure will be performed.
The network performs one of steps 3a or 3b or 3c.
3a. If the UE and network support inter-RAT cell change order to GERAN and the target cell is GERAN:
The eNodeB can trigger an inter‑RAT cell change order (optionally with NACC) to a GERAN neighbour cell by sending an RRC message to the UE. The inter-RAT cell change order may contain a CS Fallback Indicator which indicates to UE that the cell change order is triggered due to a CS fallback request. If the inter-RAT cell change order contains a CS Fallback Indicator and the UE fails to establish connection to the target RAT, then the UE considers that CS fallback has failed. Service Request procedure is considered to be successfully completed when cell change order procedure is completed successfully.
The eNodeB selects the target cell considering the PLMN ID and possibly the LAC for CS domain provided by the MME in step 1b for CCO/NACC purpose.
3b. If the UE or the network does not support inter-RAT PS handover from E-UTRAN to GERAN/UTRAN nor inter-RAT cell change order to GERAN or the network does not wish to use these procedures:
The eNodeB can trigger RRC connection release with redirection to GERAN or UTRAN.
The eNodeB sets the "CS Fallback High Priority" indication in the RRC Release message, if the S1AP message in Step 1b contains the "CSFB High Priority" indication.
NOTE 1: When performing CS Fallback to UTRAN, the RRC connection release with redirection can be optimized if both the UE and UTRAN support the optional "Deferred measurement control reading" feature specified in TS 25.331 [7].
3c. If the UE and network support "RRC connection release with redirection and Multi Cell System Information to GERAN/UTRAN":
The eNodeB can trigger RRC connection release with redirection to GERAN or UTRAN and include one or more physical cell identities and their associated System Information.
In step 3b or step 3c, the eNodeB includes the redirection control information into the RRC Connection Release message based on the PLMN ID for CS domain and the RAT/frequency priority configured in the eNodeB, so that the UE registered PLMN for CS domain can be preferably selected.
The eNodeB sets the "CS Fallback High Priority" indication in the RRC Release message, if the S1AP message in Step 1b contains the "CSFB High Priority" indication.
NOTE 2: Service Request procedure supervision timer shall be sufficiently long considering the optional measurement reporting at step 2.
4. The eNodeB sends an S1-AP UE Context Release Request message to the MME. If the target cell is GERAN and either the target cell or the UE does not support DTM the message includes an indication that the UE is not available for the PS service.
5. The MME releases the UE Context in the eNodeB as well as all eNodeB related information in the S-GW as specified in TS 23.401 [2].
In case the Cause indicates that RRC was released due to abnormal conditions, e.g. radio link failure, the MME suspends the EPS bearers (Step 8).
The UE performs one of steps 6a or 6b or 6c and THEN performs step 6d.
6a. (Step 6a is performed if step 3a, Cell Change Order to GERAN, was performed)
The UE moves to the new cell in GERAN. The UE uses the NACC information and/or the broadcast System Information and when it has all of the necessary information to access the GERAN cell, establishes a radio signalling connection.
6b. (Step 6b is performed if step 3b, RRC release with redirection, was performed).
The UE moves to the target RAT, identifies a suitable cell preferably of the same PLMN as received in LAI IE of combined EPS/IMSI Attach/TAU Accept message, receives the broadcast System Information and when it has the necessary information to access GERAN/UTRAN, establishes a radio signalling connection.
6c. (Step 6c is performed if step 3c, RRC connection release with redirection and Multi Cell System Information, was performed).
The UE moves to the target RAT and identifies a suitable cell preferably of the same PLMN as received in LAI IE of combined EPS/IMSI Attach/TAU Accept message. The UE uses the Multi Cell System Information and/or the broadcast System Information and when it has all of the necessary information to access GERAN/UTRAN, the UE establishes the radio signalling connection.
6d. When the UE arrives at the target cell, if target RAT is UTRAN: The UE establishes the radio signalling connection by sending an RRC Initial Direct Transfer message as specified in TS 25.331 [7] that contains a NAS message. The CN Domain Indicator is set to "CS" in the Initial Direct Transfer message. If the eNodeB indicated UE to go to GERAN in step 3 but the UE finally camps on an UTRAN cell of the same RA that the UE is registered with and ISR active, the UE shall locally deactivate ISR.
If target RAT is GERAN A/Gb mode: The UE establishes a radio signalling connection by using the procedures specified in TS 44.018 [4] (i.e. UE requests and is assigned a dedicated channel where it sends a SABM containing a NAS message to the BSS and the BSS responds by sending a UA). Upon receiving the SABM (containing the NAS message) the BSS sends a COMPLETE LAYER 3 INFORMATION message (containing the NAS message) to the MSC which indicates CS resources have been allocated in the GERAN cell. After the establishment of the main signalling link as described in TS 44.018 [4] the UE enters either Dual Transfer Mode or Dedicated Mode.
If the LA of the new cell is different from the one stored in the UE, the UE (which is received as part of Combined Attach/TAU procedure in E-UTRAN) shall initiate a Location Area Update regardless of the different Network Modes of Operation (NMO). The UE shall set the "follow-on request" flag in the LAU Request in order to indicate to the MSC not to release the Iu/A connection after the LAU procedure is complete. The UE shall indicate to the target MSC that this is an originating call establishment as a result of CSFB by including the CSMO flag. Further the UE performs any Routing Area Update procedure as specified by TS 23.060 [3].
When different from the serving MSC, the target MSC derives the Last Used LTE PLMN from the MAP Send Identification message received from the serving MSC/VLR during the Location Area Update procedure.
In NMO I a CSFB UE shall perform separate LAU with "follow-on request" flag and "CSMO" flag, and RAU procedures instead of a Combined RA/LA Update procedure to speed up the CSFB procedure.
7. If the target RAT is GERAN and DTM is not supported or the UE does not support DTM, the UE starts the Suspend procedure specified in TS 23.060 [3]. This triggers the (serving) SGSN to send a Suspend Request (TLLI, RAI) message to the old CN node identified by the RAI and TLLI. If ISR is not active, the RAI and TLLI refer to an MME. The MME returns a Suspend Response to the SGSN even though the GUTI cannot be derived from the P-TMSI and RAI pair. If ISR is active, the RAI and TLLI refer to the old S4-SGSN, In this case, if the serving SGSN is different from the old SGSN which has ISR association with MME, the old SGSN returns a Suspend Response to the serving SGSN.
NOTE 3: For step 7b and 8, the inter-SGSN suspending procedure of ISR active case are not shown in the figure.
8. If the S1-AP UE Context Release Request message, received from the eNodeB in step 4, indicates that the UE is not available for the PS service in the target cell, the MME deactivates GBR bearers towards S-GW and P-GW(s) by initiating MME-initiated Dedicated Bearer Deactivation procedure as specified in TS 23.401 [2], and starts the preservation and suspension of non-GBR bearers by sending Suspend Notification message to the S-GW. If ISR is active, the (old) S4-SGSN deactivates GBR bearers towards S‑GW and P‑GW(s) by initiating MS-and SGSN initiated Bearer Deactivation procedure as specified in TS 23.060 [3], and starts the preservation and suspension of non-GBR bearers by sending the Suspend Notification message to the S-GW, which is all triggered by the Suspend procedure in step 7. The S-GW sends Suspend Notification message to the P-GW(s) when it receives the Suspend Notification message from MME or S4-SGSN. If the S-GW receives two Suspend Notification messages for the same UE, it ignores the second one except for sending response. The MME stores in the UE context that UE is suspended status. If ISR is active, the (old) S4-SGSN stores in the UE context that UE is in suspended status. All the preserved non-GBR bearers are marked as suspended status in the S-GW and P-GW(s). The P-GW should discard packets if received for the suspended UE.
NOTE 4: Step 8 can not be triggered by the Suspend procedure since the full GUTI can not be derived from the P-TMSI and RAI included in the Suspend Request message.
9. The UE continues with the MO call setup procedure with sending CM Service Request. The UE shall indicate to the MSC that this is an originating call establishment as a result of CSFB by including the "CSMO" flag.
10a. If the UE is not registered in the MSC serving the 2G/3G cell or the UE is not allowed in the LA, the MSC shall reject the service request, if implicit location update is not performed.
10b. A UE detecting that the MSC rejected the service request shall perform the Location Area Update or a Combined RA/LA procedure according to existing GERAN or UTRAN procedures as specified in TS 23.060 [3] for the different Network Modes of Operation (NMO).
When different from the serving MSC, the target MSC derives the Last Used LTE PLMN from the MAP Send Identification message received from the serving MSC/VLR during the Location Area Update procedure.
10c. The UE initiates the CS call establishment procedure and the UE shall include the CSMO flag in the CM Service Request to the MSC.
11. After the CS voice call is terminated and if the UE is in GERAN and PS services are suspended, then the UE shall resume PS services as specified in TS 23.060 [3]. A Gn/Gp -SGSN will follow TS 23.060 [3] to resume the PDP Context(s); in addition, the Gn/Gp SGSN sends a Update PDP Context Request message to the GGSN/P‑GW, the GGSN/P‑GW resumes the PDP Context(s). An S4 SGSN will follow TS 23.060 [3] to resume the bearers, and informs the S-GW and P-GW(s) to resume the suspended bearers. If the UE has returned to E-UTRAN after the CS voice call was terminated, then the UE shall resume PS service by sending TAU Request to MME. If PS services resumption was unsuccessful before returning to E-UTRAN and ISR is active, the UE shall locally deactivate ISR before initiating the TAU procedure. The MME will in addition inform S-GW and P-GW(s) to resume the suspended bearers. Resuming the suspended bearers in the S-GW and in the P-GW should be done by implicit resume using the Modify Bearer request message if it is triggered by the procedure in operation, e.g. RAU, TAU or Service Request. The S-GW is aware of the suspend state of the bearers and will forward the Modify Bearer request to the P-GW. Explicit resume using the Resume Notification message should be used in cases when Modify Bearer Request is not triggered by the procedure in operation.
NOTE 5: Upon termination of CS services, if all the PDN connections have been handed over to WLAN according to procedures defined in TS 23.402 [27] the UE does not need to resume the PS traffic over the current cell.
If the UE remains on UTRAN/GERAN after the CS voice call is terminated the UE performs normal mobility management procedures as defined in TS 23.060 [3] and TS 24.008 [21].
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6.4 Mobile Originating call in Idle Mode
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Mobile Originating call in Idle Mode procedure is specified by reusing the Mobile Originating Call in Active mode procedures as specified in clauses 6.2 and 6.3 with Extended Service Request for mobile originating CS fallback to the MME where the messages S1-AP UE Context Modification Request and Response are replaced by S1-AP Initial UE Context Request and Response. The LAI is included in the S1-AP Initial UE Context Request message and sent to the eNodeB. The UE is transited to ECM-CONNECTED mode by following the applicable procedures specified in TS 23.401 [2].
NOTE: Even in case both the UE and the network support PS HO, the eNodeB may choose to use a different inter-RAT mobility procedure.
If UE has only LIPA PDN connection and the cell accessed by the UE does not link to the L-GW where the UE had the LIPA PDN Connection, the MME shall reject the Extended Service Request with a reason code which results in the UE selecting GERAN or UTRAN as specified in TS 24.301 [34].
If the UE has only SIPTO at the Local Network PDN connections:
(i) in a network with collocated L-GW deployment and the (H)eNB accessed by the UE is not collocated with the L-GW providing the SIPTO at the Local Network connectivity; or
(ii) in a network with stand-alone GW deployment and the (H)eNB accessed by the UE is not connected to the Local Network where the stand-alone GW (with S-GW and L-GW collocated) providing the SIPTO at the Local Network connectivity is residing,
the MME shall reject the Extended Service Request with an appropriate cause value which results in the UE selecting GERAN or UTRAN.
If the UE has only SIPTO at the Local Network PDN connections and LIPA PDN connections, where:
- the SIPTO at the Local Network PDN connections fulfil criterion (i) or (ii) above; and
- the cell accessed by the UE does not link to the L-GW where the UE had the LIPA PDN connection,
the MME shall also reject the Extended Service Request with an appropriate cause value which results in the UE selecting GERAN or UTRAN.
A UE with a USIM assigned to one of Access Classes 11 to 15, e.g. a UE that is a Service User according to TR 22.952 [47] sets the RRC establishment cause to "HighPriorityAccess" based on the access class handling as specified in TS 36.331 [33]. If the network supports CSFB priority call handling, the MME determines whether the CSFB request requires CSFB priority call handling of CS Fallback based on the "HighPriorityAccess" establishment cause forwarded by eNodeB to the MME and/or MPS CS Priority in the UE's EPS subscription. According to operator policy, the MME may use MPS CS Priority in the UE's EPS subscription to verify the priority handling of the CS Fallback procedure.
If the MME determines to perform CS Fallback priority call handling, based on MPS CS Priority in the UE's EPS subscription or because the call is an emergency call, it sets priority indication, i.e. "CSFB High Priority", in the S1-AP Initial UE Context Request message to the eNodeB as specified in TS 36.413 [35]. The eNodeB allocates radio bearer resources to the UE preferentially compared to other normal calls. In the case of emergency call, the MME also requests the eNodeB to inhibit roaming and access restrictions via the Additional CS Fallback Indicator as specified in TS 36.413 [35].
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6.5 Returning back to E-UTRAN
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Once CS service ends in CS domain, existing mechanisms can be used to move the UE to E‑UTRAN, no specific CS Fallback mechanisms are needed.
During the release of an RR connection the MSC should indicate to GERAN/UTRAN that the RR connection (for call or CISS or LCS) was established as a result of CS fallback. GERAN and UTRAN may use the indication to determine which of the existing mechanisms should be used to move the UE to E‑UTRAN.
When configured to support the return to the last used PLMN after CSFB, after a successful setup of an RR connection or during the release of the UTRAN RR connection, the MSC shall further indicate to GERAN/UTRAN the last used LTE PLMN ID. GERAN and UTRAN shall take the last used LTE PLMN ID into account when selecting the target cell in PS handover to E-UTRAN or when selecting the dedicated target frequency list for idle mode mobility to E-UTRAN in RR Connection Release procedure.
When the UE moves to E‑UTRAN, if the EPS service was suspended during the CS service, it is resumed according to the procedure shown in the figure 6.5‑1 below.
Figure 6.5-1: Resume Procedure returning from CS fallback no PS HO
1. The UE sends a TAU Request message, to the MME.
2. If the UE context in the MME indicates that UE is in suspended status, the MME informs the S‑GW and P-GW(s) to re-activate the EPS bearers for the UE.
If the procedure triggered by the NAS message in step 1 activates Modify Bearer Request message to the S-GW, this message should be used as an implicit resume. The S-GW is aware of the suspend state of the bearers and shall forward the Modify Bearer request to the P-GW. The P-GW and S-GW shall clear the suspend state and confirm with Modify Bearer response to the MME.
3. The NAS message is processed accordingly.
NOTE 1: If some IP traffic had been routed over WLAN as a result of CSFB, a UE can use an implementation-dependent hysteresis mechanism (e.g. based on an implementation dependent timer) to prevent the ping-pong such as traffic being handed back to the original RAT (e.g. E-UTRAN) again in a short period of time.
NOTE 2: Upon termination of CS services, if all the PDN connections have been handed over to WLAN according to procedures defined in TS 23.402 [27], when the UE returns to E-UTRAN the UE performs an attach with handover indication.
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6.6 Mobile Originated or Mobile terminated call rejected by the MME
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The MME may reject an Extended Service Request either for mobile originated or mobile terminated CSFB. The following procedure covers this scenario.
Figure 6.6-1: CSFB MO or MT call, rejected by MME
1. UE is combined EPS/IMSI attached.
2. UE makes a decision to perform a mobile originated CS call or accepts CS paging for the CS Fallback to GERAN/UTRAN.
3. UE sends an Extended Service Request for mobile originating/mobile terminating CS fallback to the MME.
4. If the MME decides to reject the Extended Service Request, the MME sends a Service Reject message to the UE.
Steps 5 – 8 are executed when Service Reject is sent with a reason code which results in the UE selecting GERAN or UTRAN, as specified in TS 24.301 [34].
5. The UE selects GERAN or UTRAN CS Domain without waiting for RRC Release.
6. The MME releases S1 by sending the S1 UE Context Release Command (Cause) message to the eNodeB. Cause value indicates that release is triggered due to CS Fallback procedure.
7. If the RRC connection is not already released, the E-UTRAN sends a RRC Connection Release message to the UE.
8. The E-UTRAN confirms the S1 Release by returning an S1 UE Context Release Complete message to the MME.
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7 Mobile Terminating Call
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7.1 General
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This clause describes the mobile terminating call procedures for the CS Fallback in EPS.
The MSC handles the timers, queuing and retransmission for sending the SGsAP-PAGING-REQUEST message on the SGs interface in the same way that it handles the sending of a PAGING message on the A or Iu interface. As a consequence, the MME and (if ISR is active) the SGSN shall not implement local retransmission schemes for this paging.
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7.2 Mobile Terminating call in idle mode
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The procedure for Mobile Terminating Call in idle mode is illustrated in figure 7.2-1, in the normal case. Clause 6.6 describes the procedure when the procedure is rejected by the MME.
Figure 7.2-1: Mobile Terminating Call in idle mode
1. G‑MSC receives IAM.
2. G‑MSC retrieves routing information of the terminating UE by Send Routing Info procedures as specified in TS 23.018 [5].
3. G‑MSC sends IAM to the MSC on the terminating side as specified in TS 23.018 [5].
4. The MME receives a Paging Request (IMSI, VLR TMSI, Location Information, eMLPP priority level indication) message from the MSC over a SGs interface. IMSI is used by the MME to find the S‑TMSI. If the TMSI and the LAI are received from the MSC/VLR, the S-TMSI is used as the paging address on the radio interface. If the TMSI is not received from the MSC/VLR, the IMSI shall be used as the paging address on the radio interface. If location information is reliably known by MME (i.e. MME stores the list of TAs), the MME shall page the UE in all the TAs. If the MME does not have a stored TA list for the UE, the MME may use the location information received from the MSC to page the UE.
NOTE 1: The case when LAI is not received from MSC/VLR and the case when S-TMSI is not available are further described in clause 4.8.
NOTE 2: This procedure takes place before step 3, immediately after MSC receives MAP_PRN from HSS, if pre-paging is deployed.
If the MME receives a Paging Request message for an UE which is considered as detach for EPS services, the MME sends the Paging reject message to the MSC with an appropriate cause value. This rejection triggers the MSC to page the UE over A or Iu-cs interface.
NOTE 3: In case of a CS fallback capable UE in NMO II, there is a case where, for example, the MME releases the SGs association due to the UE idle mode mobility while the VLR still maintains the SGs association.
If the MME holds stored Paging Restriction information (see TS 23.401 [2]) for the UE that restricts the SGs Paging Request from causing paging, the MME sends the SGs Paging Reject message to the MSC containing an appropriate cause. The rest of the steps in the procedure are skipped.
If the MME receives Paging Request with eMLPP priority level indication from the MSC, then the MME determines based on its configuration whether this priority level requires CSFB priority call handling.
5. If the MME did not return an "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME sends a Paging (as specified in TS 23.401 [2]) message to each eNodeB. The Paging message includes a suitable UE Identity (i.e. S‑TMSI or IMSI) and a CN Domain Indicator that indicates which domain (CS or PS) initiated the paging message. In this case it shall be set to "CS" by the MME.
If the MME returned the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME shall not send the paging to the eNodeBs and sends Paging Reject towards MSC to stop CS Paging procedure and this CSFB procedure stops.
If the MME determined in step 4 that CSFB priority call handling shall apply, the MME sets the priority level in the S1AP Paging message based on the value(s) configured in the MME for CSFB priority call handling.
6. The radio resource part of the paging procedure takes place. The message contains a suitable UE Identity (i.e. S‑TMSI or IMSI) and a CN Domain indicator. The eNodeB performs the paging procedure according to the priority level received with the S1AP Paging Request.
7a. The UE establishes an RRC connection and sends an Extended Service Request for mobile terminating CS fallback to MME. The UE indicates its S-TMSI in the RRC signalling. The Extended Service Request message is encapsulated in RRC and S1‑AP messages. The MME sends the SGs Service Request message to the MSC containing an indication that the UE was in idle mode (and hence, for example, that the UE has not received any Calling Line Identification information). Receipt of the SGs Service Request message stops the MSC retransmitting the SGs interface Paging message.
NOTE 4: In order to avoid the calling party experiencing a potentially long period of silence, the MSC may use the SGs Service Request message containing the idle mode indication as a trigger to inform the calling party that the call is progressing.
If the UE, when in MUSIM mode, upon reception of paging indication in E-UTRAN access decides not to accept the paging, the UE attempts to send a Reject Paging Indication in the Extended Service Request message unless it is unable to do so e.g. due to UE implementation constraints. The MME sends the SGs Paging Reject message to the MSC containing an appropriate cause. The UE remains reachable for future paging attempts based on stored (if any) Paging Restriction Information in the MME. The rest of the steps in the procedure are skipped.
If the MME determined in step 4 that CSFB priority call handling shall apply and the MME receives subsequent Extended Service Request in Step 7a, it detects this message is the response to the priority CS Fallback procedure initiated in step5. In this case, the MME processes this message with priority and set the priority indication, i.e. "CSFB High Priority", in step7b as specified in TS 36.413 [35].
If UE has only LIPA PDN connection and the cell accessed by the UE does not link to the L-GW where the UE had the LIPA PDN Connection, the MME shall reject the Extended Service Request with a reason code which results in the UE selecting GERAN or UTRAN as specified in TS 24.301 [34].
If the UE has only SIPTO at the Local Network PDN connections:
(i) in a network with collocated L-GW deployment and the (H)eNB accessed by the UE is not collocated with the L-GW providing the SIPTO at the Local Network connectivity; or
(ii) in a network with stand-alone GW deployment and the (H)eNB accessed by the UE is not connected to the Local Network where the stand-alone GW (with S-GW and L-GW collocated) providing the SIPTO at the Local Network connectivity is residing,
the MME shall reject the Extended Service Request with an appropriate cause value which results in the UE selecting GERAN or UTRAN.
If the UE has only SIPTO at the Local Network PDN connections and LIPA PDN connections, where:
- the SIPTO at the Local Network PDN connections fulfil criterion (i) or (ii) above; and
- the cell accessed by the UE does not link to the L-GW where the UE had the LIPA PDN connection,
the MME shall also reject the Extended Service Request with an appropriate cause value which results in the UE selecting GERAN or UTRAN.
7b. MME sends S1‑AP: Initial UE Context Setup (UE capabilities, CS Fallback Indicator, LAI and other parameters specified in TS 23.401 [2]) to indicate the eNodeB to move the UE to UTRAN/GERAN. The registered PLMN for CS domain is identified by the PLMN ID included in the LAI, which is allocated by the MME.
7c. The eNodeB shall reply with S1-AP: Initial UE Context Setup Response message.
8a. If the eNodeB knows that both the UE and the network support PS handover: The information flow may continue as described in clause 7.3 "Mobile Terminating call in Active Mode - PS HO supported" from step 2, in clause 7.3, and onwards.
. If the eNodeB knows that either the UE or the network does not support PS handover: The information flow shall continue as described in clause 7.4 "Mobile Terminating call in Active Mode – No PS HO support" from step 2, in clause 7.4, and onwards.
NOTE 5: Even in case both the UE and the network support PS HO, the eNodeB may choose to use a different inter-RAT mobility procedure.
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aac84734dd828878c9914c9a3545338d
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23.272
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7.3 Mobile Terminating call in Active Mode - PS HO supported
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This flow may be executed when the eNodeB knows that both the UE and the network support PS HO in the normal case. Clause 6.6 describes the procedure when the procedure is rejected by the MME.
Figure 7.3-1: CS Page in E-UTRAN, Call in GERAN/UTRAN
1a. The MSC receives an incoming voice call and responds by sending a Paging Request (IMSI or TMSI, optional Caller Line Identification and Connection Management information, CS call indicator, eMLPP priority level indication) to the MME over a SGs interface. The MSC only sends a CS Page for an UE that provides location update information using the SGs interface. In active mode the MME has an established S1 connection and if the MME did not return the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME reuses the existing connection to send the CS Service Notification to the UE.
If the MME returned the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME shall not send the CS Service Notification to the UE and shall send Paging Reject towards MSC to stop CS Paging procedure, and this CSFB procedure stops.
If the X2-based or S1-based handover procedure is ongoing when the MME receives a Paging Request over the SGs interface, the MME shall follow the procedures as specified in clauses 5.5.1.1.1 and 5.5.1.2.1 of TS 23.401 [2] for X2-based handover and S1-based handover respectively.
If the Inter RAT handover procedure is ongoing when the MME receives a Paging Request over the SGs interface, the MME shall simply discard this message and no further action is performed by MME. In this case, mobile terminating call can be continued by the MSC retransmitting Paging message as specified in TS 29.118 [44].
The eNodeB forwards the CS Service Notification message to the UE. The message contains CN Domain indicator and, if received from the MSC, the Caller Line Identification.
The MME sends the SGs Service Request message to the MSC containing an indication that the UE was in connected mode. The MSC uses this connected mode indication to start the Call Forwarding on No Reply timer for that UE and the MSC should send an indication of user alerting to the calling party. Receipt of the SGs Service Request message stops the MSC retransmitting the SGs interface Paging message.
NOTE 1: The pre‑configured policy may be used by UE to avoid being disturbed without Caller Line Identification display and the detailed handling is to be decided by CT1 and CT6.
NOTE 2: This procedure can also take place immediately after MSC receives MAP_PRN from HSS, if pre-paging is deployed. Caller Line Identification and CS call indicator are also provided in the case of pre-paging.
NOTE 3: In order to avoid the calling party experiencing a potentially long period of silence, the MSC may use the SGs Service Request message as a trigger to inform the calling party that the call is progressing.
If the MME receives paging request message with eMLPP priority level indication from the MSC, then the MME determines based on its configuration whether this priority level requires CSFB priority call handling.
1b. UE sends an Extended Service Request (Reject or Accept) message to the MME for mobile terminating CS fallback. The Extended Service Request message is encapsulated in RRC and S1‑AP messages. The UE may decide to reject CSFB based on Caller Line Identification.
1c. Upon receiving the Extended Service Request (Reject) for mobile terminating CS fallback, the MME sends Paging Reject towards MSC to stop CS Paging procedure and this CSFB procedure stops.
1d. MME sends an S1‑AP UE Context Modification Request (CS Fallback Indicator, LAI) message to eNodeB. This message: indicates to the eNodeB that the UE should be moved to UTRAN/GERAN. The registered PLMN for CS domain is identified by the PLMN ID included in the LAI, which is allocated by the MME.
If MME determined in Step 1a that CSFB priority call handling shall apply, the MME sends S1-AP UE Context Modification Request message to the eNodeB with priority indication, i.e. "CSFB High Priority", as specified in TS 36.413 [35].
1e. The eNodeB shall reply with S1-AP UE Context Modification Response message.
2. The eNodeB may optionally solicit a measurement report from the UE to determine the target GERAN/UTRAN cell to which PS handover will be performed.
NOTE 4: Based on operator policy, the priority indicator received in step1b may be used by eNodeB to decide whether to continue CS Fallback procedures with PS HO, i.e. step3a, or to initiate radio release procedure to redirect the UE to 2G/3G Circuit Switch.
3a. The eNodeB triggers PS handover to a GERAN/UTRAN neighbour cell by sending a Handover Required message to MME. The eNodeB selects the target PS handover cell considering the PLMN ID and possibly the LAC for CS domain provided by the MME in step 1d.
If the eNB is a HeNB, the HeNB should perform step 3 through step 6 of clause 7.4 instead of PS HO if the HeNB detects that the UE has only LIPA PDN Connections. CSFB will not be completed successfully when PS HO is performed if the UE has only LIPA PDN Connections as PS HO would result in the MME detaching the UE.
NOTE 5: For details how the HeNodeB determines whether a PDN connection is a LIPA PDN connection see TS 23.401 [2], clause 4.3.16.
In the following an inter-RAT handover from E‑UTRAN to UTRAN or GERAN as specified in TS 23.401 [2] begins. The eNodeB indicates in the Source RNC to Target RNC Transparent container that PS handover was triggered due to CSFB. The eNodeB also indicates whether CSFB was triggered for emergency or priority call handling purpose. If the network supports a priority call handling, the eNodeB may forward the priority indication to the target GERAN/UTRAN in the Source to Target Transparent Container, and the target GERAN/UTRAN allocates radio bearer resources taking received priority indication take into account. As part of this handover, the UE receives a HO from E‑UTRAN Command and tries to connect to a cell in the target RAT. The HO from E-UTRAN Command may contain a CS Fallback Indicator which indicates to UE that the handover was triggered due to a CS fallback request. If the HO from E-UTRAN Command contains a CS Fallback Indicator and the UE fails to establish connection to the target RAT, then the UE considers that CS fallback has failed.
The UE establishes the signalling connection as described in step 4b.
NOTE 6: During the PS HO the SGSN does not create a Gs association with the MSC/VLR.
3b. If the target RAT is GERAN and the UE has entered Dedicated Mode, the UE starts the Suspend procedure (see TS 44.018 [4]) unless both the UE and the Target cell support DTM in which case TBF re-establishment may be performed.
3c. A Gn/Gp-SGSN that receives the Suspend message from the UE follows the Suspend procedure specified in TS 23.060 [3], clause 16.2.1.1.1.
An S4-SGSN that receives the Suspend message from the UE follows the Suspend procedure specified in TS 23.060 [3]. The S4-SGSN deactivates GBR bearers towards S-GW and P-GW(s) by initiating MS-and SGSN Initiated Bearer Deactivation procedure as specified in TS 23.060 [3], and starts the preservation and suspension of non-GBR bearers by sending Suspend Notification message to the S-GW. The S-GW releases all RNC related information (address and TEIDs) for the UE if Direct Tunnel is established, and sends Suspend Notification message to the P-GW(s). The SGSN stores in the UE context that UE is in suspended status. All the preserved non-GBR bearers are marked as suspended status in the S-GW and P-GW(s). The P-GW should discard packets if received for the suspended UE.
4a. If the LA of the new cell is different from the one stored in the UE, the UE shall initiate a Location Area Update procedure as follows:
- If the network is operating in NMO-I (Network Modes of Operation), the UE shall initiate a separate Location Area Update before initiating the RAU procedure instead of a Combined RA/LA Update procedure (to speed up the CSFB procedure); or
- if the network is operating in NMO-II the UE shall initiate a Location Area Update procedure before initiating the RAU procedure required for PS handover.
The UE shall set the "CSMT" flag in the LAU Request. The "CSMT" flag is used to avoid missing MT call in roaming retry case. Further the UE performs any Routing Area Update procedure as specified in TS 23.060 [3].
The UE may initiate a Location Area Update procedure immediately when the UE is handed over to the target cell i.e. before the UE receives e.g. LAI or NMO information as part of the RAN Mobility Information.
When the MSC receives a LA Update Request, it shall check for pending terminating CS calls and, if the "CSMT" flag is set, maintain the CS signalling connection after the Location Area Update procedure for pending terminating CS calls.
4b. If the UE does not initiate a LAU procedure, it shall respond with a Paging Response message to the MSC as follows:
- If the Target RAT is UTRAN or GERAN Iu mode: The UE establishes a radio signalling connection and responds to the paging by sending an RRC Paging Response as specified in TS 25.331 [7]. The CN Domain Indicator is set to "CS" in the Initial Direct Transfer message.
- If the Target RAT is GERAN A/Gb mode: The UE establishes a radio signalling connection and responds to paging by using the procedures specified in TS 44.018 [4] (i.e. UE requests and is assigned a dedicated channel where it sends a SABM containing a Paging Response to the BSS and the BSS responds by sending a UA). Upon receiving the SABM (containing a Paging Response message) the BSS sends a COMPLETE LAYER 3 INFORMATION message (containing a Paging Response message) to the MSC which indicates CS resources have been allocated in the GERAN cell. If both the UE and the target cell support enhanced CS establishment in DTM (indicated by GERAN system information included within the HO from E‑UTRAN Command) an RR connection may be established while in packet transfer mode without release of the packet resources, see TS 43.055 [24]. After the establishment of the main signalling link as described in TS 44.018 [4] the UE enters either Dual Transfer Mode or Dedicated Mode and the CS call establishment procedure completes.
NOTE 7: The BSS should be prepared to receive a Paging Response even when the corresponding Paging Request has not been sent by this BSS.
5a. After performing the LAU procedure or after receiving the Paging Response the MSC shall establish the CS call if the UE is allowed in the LA.
5b. If the UE is not registered in the MSC that receives the Paging Response or the UE is not allowed in the LA, the MSC shall reject the Paging Response message by releasing the A/Iu-CS. The BSC/RNC in turn releases the signalling connection for UTRAN or GERAN CS domain. The signalling connection release shall trigger the UE to obtain the LAI, which causes the initiation of a Location Area Update or a Combined RA/LA procedure as specified in TS 23.060 [3] for the different Network Modes of Operation (NMO).
The Location Area Update triggers the Roaming Retry for CS Fallback procedure as defined in clause 7.5.
5c. After performing the LAU procedure the MSC shall establish the CS call if the UE is allowed in the LA.
6. The UE performs any remaining steps of the inter-RAT handover from E-UTRAN to UTRAN or GERAN as specified in TS 23.401 [2]
With the exception of steps 1a and 1c, above, Call Forwarding (see TS 23.082 [31]) is performed on the basis of the TS 24.008 [21] signalling received on the GERAN/UTRAN cell.
If the UE remains on UTRAN/GERAN after the CS voice call is terminated the UE performs normal mobility management procedures as defined in TS 23.060 [3] and TS 24.008 [21].
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23.272
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7.4 Mobile Terminating call in Active Mode - No PS HO support
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This procedure is executed when PS HO is not supported, in the normal case. Clause 6.6 describes the procedure when the procedure is rejected by the MME.
Figure 7.4-1: CS Page in E-UTRAN, Call in GERAN/UTRAN without PS HO
1a. The MSC receives an incoming voice call and responds by sending a Paging Request (IMSI or TMSI, optional Caller Line Identification and Connection Management information, eMLPP priority level indication) to the MME over a SGs interface. The MSC only sends a CS Page for an UE that provides location update information using the SGs interface. In active mode the MME has an established S1 connection and if the MME did not return the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME reuses the existing connection to send the CS Service Notification to the UE.
If the MME returned the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME shall not send the CS Page to the UE and sends CS Paging Reject towards MSC to stop CS Paging procedure, and this CSFB procedure stops.
If the X2-based or S1-based handover procedure is ongoing when the MME receives a Paging Request over the SGs interface, the MME shall follow the procedures as specified in clauses 5.5.1.1.1 and 5.5.1.2.1 of TS 23.401 [2] for X2-based handover and S1-based handover respectively.
If the Inter RAT handover procedure is ongoing when the MME receives a Paging Request over the SGs interface, the MME shall simply discard this message and no further action is performed by MME. In this case, mobile terminating call can be continued by the MSC retransmitting Paging message as specified in TS 29.118 [44].
The eNodeB forwards the CS Service Notification message to the UE. The message contains CN Domain indicator and, if received from the MSC, the Caller Line Identification.
The MME sends the SGs Service Request message to the MSC containing an indication that the UE was in connected mode. The MSC uses this connected mode indication to start the Call Forwarding on No Reply timer for that UE and the MSC should send an indication of user alerting to the calling party. Receipt of the SGs Service Request message stops the MSC retransmitting the SGs interface Paging message.
NOTE 1: The pre‑configured policy may be used by UE to avoid being disturbed without Caller Line Identification display and the detailed handling is to be decided by CT WG1 and CT WG6.
NOTE 2: This procedure can also take place immediately after MSC receives MAP_PRN from HSS, if pre-paging is deployed. Caller Line Identification is also provided in the case of pre-paging.
If the MME receives paging request message with eMLPP priority level indication from the MSC, then the MME determines based on its configuration whether this priority level requires CSFB priority call handling.
1b. UE sends an Extended Service Request (Reject or Accept) message to the MME for mobile terminating CS fallback. Extended Service Request message is encapsulated in RRC and S1‑AP messages. The UE may decide to reject CSFB based on Caller Line Identification.
1c. Upon receiving the Extended Service Request (Reject) for mobile terminating CS fallback, the MME sends Paging Reject towards MSC to stop CS Paging procedure and this CSFB procedure stops.
1d. The MME sends an S1‑AP UE Context Modification Request (CS Fallback Indicator, LAI) message to eNodeB. This message indicates to the eNodeB that the UE should be moved to UTRAN/GERAN. The registered PLMN for CS domain is identified by the PLMN ID included in the LAI, which is allocated by the MME.
If MME determined in Step 1a that CSFB priority call handling shall apply, the MME sends S1-AP UE Context Modification Request message to the eNodeB with priority indication, i.e. "CSFB High Priority", as specified in TS 36.413 [35].
1e. The eNodeB shall reply with S1-AP UE Context Modification Response message.
2. The eNodeB may optionally solicit a measurement report from the UE to determine the target GERAN/UTRAN cell to which the redirection procedure will be performed.
The network performs one of steps 3a or 3b or 3c.
3a. If the UE and network support inter-RAT cell change order to GERAN and the target cell is GERAN:
The eNodeB can trigger an inter‑RAT cell change order (optionally with NACC) to a GERAN neighbour cell by sending an RRC message to the UE. The inter-RAT cell change order may contain a CS Fallback Indicator which indicates to UE that the cell change order is triggered due to a CS fallback request. If the inter-RAT cell change order contains a CS Fallback Indicator and the UE fails to establish connection to the target RAT, then the UE considers that CS fallback has failed. Service Request procedure is considered to be successfully completed when cell change order procedure is completed successfully.
The eNodeB selects the target cell considering the PLMN ID and possibly the LAC for CS domain provided by the MME in step 1d for CCO/NACC purpose.
3b. If the UE or the network does not support inter-RAT PS handover from E-UTRAN to GERAN/UTRAN nor inter-RAT cell change order to GERAN:
The eNodeB can trigger RRC connection release with redirection to GERAN or UTRAN instead of PS HO or NACC.
NOTE 3: When performing CS Fallback to UTRAN, the RRC connection release with redirection can be optimized if both the UE and UTRAN support the optional "Deferred measurement control reading" feature specified in TS 25.331 [7].
3c. If the UE and network support "RRC connection release with redirection and Multi Cell System Information to GERAN/UTRAN":
The eNodeB can trigger RRC connection release with redirection to GERAN or UTRAN and include one or more physical cell identities and their associated System Information.
In step 3b or step 3c, the eNodeB includes the redirection control information into the RRC Connection Release message based on the PLMN ID for CS domain and the RAT/frequency priority configured in the eNodeB, so that the UE registered PLMN for CS domain can be preferably selected.
Also in Steps 3b or 3c, the eNB sets the "CS Fallback High Priority" indication in the RRC Release message, if the S1AP message in Step 1d contains the "CSFB High Priority" indication.
NOTE 4: Service Request procedure supervision timer shall be sufficiently long considering the optional measurement reporting at step 2.
4. The eNodeB sends an S1-AP UE Context Release Request message to the MME. If the target cell is GERAN and either the target cell or the UE does not support DTM the message includes an indication that the UE is not available for PS service.
5. The MME releases the UE Context in the eNodeB as well as all eNodeB related information in the S-GW as specified in TS 23.401 [2].
In case the Cause indicates that RRC was released due to abnormal conditions, e.g. radio link failure, the MME suspends the EPS bearers (Step 8).
The UE performs one of steps 6a or 6b or 6c and THEN performs step 6d.
6a. (Step 6a is performed if step 3a, Cell Change Order to GERAN, was performed).
The UE moves to the new cell in GERAN. The UE uses the NACC information and/or the broadcast System Information and when it has the necessary information to access the GERAN cell, establishes a radio signalling connection.
6b. (Step 6b is performed if step 3b, RRC release with redirection, was performed).
The UE moves to the target RAT, identifies a suitable cell preferably of the same PLMN as received in LAI IE of combined EPS/IMSI Attach/TAU Accept message,, receives the broadcast System Information and when it has the necessary information to access GERAN/UTRAN, establishes a radio signalling connection.
6c. (Step 6c is performed if step 3c, RRC connection release with redirection and Multi Cell System Information, was performed)
The UE moves to the target RAT and identifies a suitable cell preferably of the same PLMN as received in LAI IE of combined EPS/IMSI Attach/TAU Accept message. The UE uses the Multi Cell System Information and/or the broadcast System Information and when it has the necessary information to access GERAN/UTRAN, the UE establishes the radio signalling connection.
If the UE receives the "CS Fallback High Priority" indication in the RRC Release message in Step 3b or 3c and the target is UTRAN, the UE sets the establishment cause value to "Terminating High Priority Signalling" in the RRC Connection Request in Steps 6b and 6c. If the target is GERAN, no special establishment cause value is set by the UE.
6d. If the LA of the new cell is different from the one stored in the UE, the UE shall initiate a Location Area Update regardless of the different Network Modes of Operation (NMO). The UE shall set the "CSMT" flag in the LAU Request. The "CSMT" flag is used to avoid missing MT call in roaming retry case. In NMO I, the UE in GERAN may perform LA update over the RR connection instead of combined RA/LA update over the packet access as defined in TS 24.008 [21], clause 4.7.5.2.5, unless enhanced CS establishment in DTM is supported. Further the UE performs any Routing Area Update procedure as specified in TS 23.060 [3].
In NMO I a CSFB UE shall perform LAU (and if it does so, shall set the "CSMT" flag) and RAU procedures instead of a Combined RA/LA Update procedure to speed up the CSFB procedure.
When the MSC receives a LA Update Request, it shall check for pending terminating CS calls and, if the "CSMT" flag is set, maintain the CS signalling connection after the Location Area Update procedure for pending terminating CS calls.
If the eNodeB indicated UE to go to GERAN in step 3 but the UE finally camps on an UTRAN cell of the same RA that the UE is registered with and ISR active, the UE shall locally deactivate ISR.
7. If the target RAT is GERAN and DTM is not supported or the UE does not support DTM, the UE starts the Suspend procedure specified in TS 23.060 [3]. This triggers the (serving) SGSN to send a Suspend Request (TLLI, RAI) message to the old CN node identified by the RAI and TLLI. If ISR is not active, the RAI and TLLI refer to an MME. The MME returns a Suspend Response to the SGSN even though GUTI cannot be derived from the P-TMSI and RAI pair. If ISR is active, the RAI and TLLI refer to the old S4-SGSN, In this case, if the serving SGSN is different from the old SGSN which has ISR association with MME, the old SGSN returns a Suspend Response to the serving SGSN.
NOTE 5: For step 7b and 8, the inter-SGSN suspending procedure of ISR active case are not shown in the figure.
8. If the S1-AP UE Context Release Request message, received from the eNodeB in step 4, indicates that the UE is not available for the PS services in the target cell, the MME deactivates GBR bearers towards S-GW and P-GW(s) by initiating MME-initiated Dedicated Bearer Deactivation procedure as specified in TS 23.401 [2], and starts the preservation and suspension of non-GBR bearers by sending Suspend Notification message to the S-GW. If ISR is active, the (old) S4-SGSN deactivates GBR bearers towards S‑GW and P‑GW(s) by initiating MS-and SGSN initiated Bearer Deactivation procedure as specified in TS 23.060 [3], and starts the preservation and suspension of non-GBR bearers by sending the Suspend Notification message to the S-GW, which is all triggered by the Suspend procedure in step 7. The S-GW sends Suspend Notification message to the P-GW(s) when it receives the Suspend Notification message from MME or S4-SGSN. If the S-GW receives two Suspend Notification messages for the same UE, it ignores the second one except for sending response. The MME stores in the UE context that the UE is in suspended status. If ISR is active, the (old) S4-SGSN stores in the UE context that UE is in suspended status. All the preserved non-GBR bearers are marked as suspended status in the S-GW and P-GW(s). The P-GW should discard packets if received for the suspended UE.
NOTE 6: Step 8 can not be triggered by the Suspend procedure since the full GUTI can not be derived from the P‑TMSI and RAI included in the Suspend Request message.
9. If the UE does not initiate a LAU procedure, the UE responds to the paging by sending a Paging Response message as specified in TS 44.018 [4] or TS 25.331 [7]. When received at the BSS/RNS, the Paging Response is forwarded to the MSC.
NOTE 7: The MSC should be prepared to receive a Paging Response after a relatively long time from when the CS Paging Request was sent (step 1a).
9a. If UE is registered in the MSC serving the 2G/3G cell and the UE is allowed in the LA the MSC shall establish the CS call.
9b. If the UE is not registered in the MSC that receives the Paging Response or the UE is not allowed in the LA, the MSC shall reject the Paging Response by releasing the A/Iu-cs connection. The BSS/RNS in turn releases the signalling connection for CS domain.
9c. The signalling connection release shall trigger the UE to obtain the LAI, which causes the initiation of a Location Area Update or a Combined RA/LA procedure as specified in TS 23.060 [3] for the different Network Modes of Operation (NMO).
The Location Area Update triggers the Roaming Retry for CS Fallback procedure as defined in clause 7.5.
After performing the LAU procedure the MSC shall establish the CS call if the UE is allowed in the LA.
With the exception of steps 1a and 1c, above, Call Forwarding (see TS 23.082 [31]) is performed on the basis of the TS 24.008 [21] signalling received on the GERAN/UTRAN cell.
After the CS voice call is terminated and if the UE is still in GERAN and PS services are suspended, then the UE shall resume PS services as specified in TS 23.060 [3]. A Gn/Gp- SGSN will follow TS 23.060 [3] to resume the PDP Context(s), which is done by the Routing Area Update procedure. During the Routing Area Update procedure in which the Gn/Gp SGSN sends a Update PDP Context Request message to the GGSN/P‑GW, the GGSN/P‑GW resumes the PDP Context(s). An S4 SGSN will follow TS 23.060 [3] to resume the bearers, and informs the S-GW and P-GW(s) to resume the suspended bearers. If the UE has returned to E-UTRAN after the CS voice call was terminated, then the UE shall resume PS service by sending TAU Request to MME. If PS services resumption was unsuccessful before returning to E-UTRAN and ISR is active, the UE shall locally deactivate ISR before initiating the TAU procedure. The MME will in addition inform S-GW and P-GW(s) to resume the suspended bearers. Resuming the suspended bearers in the S-GW and in the P-GW should be done by implicit resume using the Modify Bearer request message if it is triggered by the procedure in operation e.g. RAU, TAU or Service Request. The S-GW is aware of the suspend state of the bearers and shall forward the Modify Bearer request to the P-GW. Explicit resume using the Resume Notification message should be used in cases when Modify Bearer Request is not triggered by the procedure in operation.
NOTE 8: Upon termination of CS services, if all the PDN connections have been handed over to WLAN according to procedures defined in TS 23.402 [27], when the UE returns to E-UTRAN the UE performs an attach with handover indication.
If the UE remains on UTRAN/GERAN after the CS voice call is terminated the UE performs normal mobility management procedures as defined in TS 23.060 [3] and TS 24.008 [21].
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7.5 Roaming Retry for CS fallback
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The procedure in this clause may be applied for mobile terminated calls where the MSC, to which the UE sends the LAU, is different from the MSC that sent the paging message to the UE. The procedure is based on the "Mobile Terminating Roaming Retry Call" procedure defined in TS 23.018 [5] and there is an only minor adaptation of the procedure to support CS fallback.
Figure 7.5-1: Roaming Retry for CS fallback
There are only 2 differences in this procedure compared to the "Mobile Terminating Roaming Retry Call" procedure defined in TS 23.018 [5].
- The first difference is that the paging message in E-UTRAN triggers the CS fallback which is followed by a location update in the new RAT. This functionality is already supported in the CS fallback flows for terminating calls and no additional functionality is needed.
- The second difference is that the UE includes the "CSMT" flag in the location update request message so that the signalling link is maintained for longer in case the IAM is delayed by the HLR.
NOTE: Roaming Retry for CS fallback procedure is not designed to provide the target MSC/VLR with the information required for allowing UE return to the last used LTE PLMN after CSFB. If this is required for a certain deployment, Roaming Forwarding for CS fallback could be used.
7.5a Roaming Forwarding for CS fallback
The procedure in this clause may be applied for mobile terminated calls where the MSC/VLR, to which the UE sends the LAU, is different from the MSC/VLR that sent the paging message to the UE. The procedure is based on the "Mobile Terminating Roaming Forwarding" procedure defined in TS 23.018 [5]; the specific behaviour for CSFB is described in this clause. This procedure avoids impacting all GMSC nodes and can coexist with Mobile Terminating Roaming Retry procedure described in clause 7.5.
NOTE 1: In order to support Mobile Terminating Roaming Forwarding both the MSC controlling the target cell, the MSC that sent the paging message to the UE and the HLR need to support the feature.
NOTE 2: This procedure has smaller call setup delay than Mobile Terminating Roaming Retry procedure especially in roaming cases.
NOTE 3: If the network does not support this procedure, the Mobile Terminating Roaming Retry procedure specified in clause 7.5 can be used.
In order to ensure roaming forwarding can be offered in all scenarios (e.g. in case of IMSI in the LAU Request from UE), HLRs should be updated to support MTRF. In order to permit Mobile Terminating Roaming Forwarding from the old VLR if the HLR is not updated to support MTRF but the visited network does support MTRF, the new VLR may include MTRF supported flag in Send Identification when it receives a Location Updating Request containing the "CSMT" flag.
Figure 7.5a-1: Roaming Forwarding for CSFB
The main differences compared to the "Mobile Terminating Roaming Forwarding" procedure defined in TS 23.018 [5] are described below:
- The paging message in E-UTRAN triggers the CS fallback which is followed by a location update in the new RAT.
NOTE 4: This functionality is already supported in the CS fallback flows for terminating calls and no additional functionality is needed.
- The UE includes the "CSMT" flag in the location update request message so that the signalling link is maintained for longer in case the IAM is delayed by the old MSC/VLR.
- If the Location Update Request contains the "CSMT" flag set and a valid TMSI/old LAI, the new MSC/VLR may indicate to the old MSC/VLR that it supports MTRF in the Send Identification message. The new VLR then performs authentication to the Location update and updates the HSS. If the Location Update Request contains the IMSI, only HLR-based MTRF procedure can be used.
- After Cancel Location is received from HSS, if the HLR authorised the MTRF call between the old and the new terminating MSCs or if the HLR did not disallow the MTRF call between the old and the new terminating MSCs but the new MSC/VLR indicated its MTRF support earlier in Send Identification message, the old MSC/VLR stops paging timer and checks roaming and charging pre-configured agreements with regards to call routeing to the new MSC/VLR. If these checks are successful, the old MSC/VLR sends a Provide Roaming Number request (MTRF Indicator, parameters received from the HLR) to the new MSC/VLR.
- In a MT CSFB call, last used LTE PLMN identity may be added in the Provide Roaming Number Request message from old MSC/VLR to new MSC/VLR, based on configuration.
7.5b Coexistence of Roaming Retry and Roaming Forwarding for CS fallback
If an MSC/VLR supports both the procedures as specified in clause 7.5 and 7.5a, and the GMSC has indicated support roaming retry as specified in clause 7.5, the old MSC/VLR which sends the initial paging request can decide based on operator policy whether to follow the procedure specified in clause 7.5 or clause 7.5a.
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7.6 Returning back to E-UTRAN
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Once CS service ends in CS domain, existing mechanisms can be used to move the UE to E-UTRAN, no specific CS Fallback mechanisms are needed.
During the release of an RR connection the MSC should indicate to GERAN/UTRAN that the RR connection (for call or CISS or LCS) was established as a result of CS fallback. GERAN and UTRAN may use the indication to determine which of the existing mechanisms that should be used to move the UE to E‑UTRAN.
When configured to support the return to the last used PLMN after CSFB, after a successful setup of an RR connection or during the release of the UTRAN RR connection, the MSC shall further indicate to GERAN/UTRAN the last used LTE PLMN ID. GERAN and UTRAN shall take the last used LTE PLMN ID into account when selecting the target cell in PS handover to E-UTRAN or when selecting the dedicated target frequency list for idle mode mobility to E-UTRAN in RR Connection Release procedure.
When the UE moves to E-UTRAN, if the EPS service was suspended during the CS service, it is resumed as specified in clause 6.5.
NOTE 1: If some IP traffic had been routed over WLAN as a result of CSFB, a UE can use an implementation-dependent hysteresis mechanism (e.g. based on an implementation dependent timer) to prevent the ping-pong such as traffic being handed back to the original RAT (e.g. E-UTRAN) again in a short period of time.
NOTE 2: Upon termination of CS services, if all the PDN connections have been handed over to WLAN according to procedures defined in TS 23.402 [27], when the UE returns to E-UTRAN the UE performs an attach with handover indication.
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7.7 Interaction with ISR
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7.7.1 Void
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7.7.2 Mobile Terminating Call when ISR is active and SGs is active between MSC/VLR and MME
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Figure 7.7.2-1: Mobile Terminating Call when ISR is active and SGs is active between MSC/VLR and MME
1) G-MSC receives IAM.
2) G-MSC retrieves routing information of the terminating UE by Send Routing Info procedures as specified in TS 23.018 [5].
3) G-MSC sends IAM to the MSC/VLR on the terminating side as specified in TS 23.018 [5].
4) The MSC/VLR sends a Page message to the MME via SGs (details on the Page message can be found in clauses 7.2 or 7.3).
5a) The MME receives the Page message from the MSC/VLR. If the UE is in ECM‑IDLE state, the MME sends a Paging (as specified in TS 23.401 [2], and CN Domain Indicator) message to each eNodeB serving the TA list the UE is registered to as specified in clause 7.2. If the UE is in ECM-CONNECTED, the MME relays the CS Page message to the serving eNodeB over the S1 interface as specified in clause 7.3.
5b) The eNodeBs receive CS paging messages from the MME, and the procedures take place as specified in clause 7.2.
6a) As ISR is active and the UE is in ECM_IDLE state, the MME forwards the CS paging message received from the MSC/VLR to the associated SGSN. The MME gets the SGSN information in the regular ISR activation process. If MME received the eMLPP priority level in step 4, it forwards the CS paging message with the eMLPP priority level to the SGSN.
6b) The SGSN receives the CS paging message from the MME, the SGSN sends paging messages to RNS/BSSs, which is described in detail in TS 23.060 [3].
The SGSN shall not implement a local retransmission scheme for the Iu/Gb paging messages.
6c) When RNS/BSS nodes receive paging message from the SGSN, paging is initiated as described in detail in TS 23.060 [3].
NOTE: If ISR is not active or the UE is in ECM-CONNECTED state, the MME does not send the CS paging message to the SGSN. That means, the steps of 6a, 6b, 6c are not needed in the MT call procedure.
7) Upon receipt of a Paging Request message for a circuit-switched service, the CS Fallback (as defined in this specification) or Cell Reselection (as defined in TS 23.060 [3]) take place, and the UE accesses CS domain from UMTS/GSM.
8) When the CS Fallback or Cell Reselection completes, the UE responds to the CS paging request and returns the CS paging response as described in detail in this specification and TS 23.060 [3] to the RNS/BSS.
9) When received at the RNS/BSS, the CS Paging Response message is sent to the MSC/VLR as described in detail in TS 23.060 [3]. The MSC/VLR receives CS paging response contained in corresponding message which shall then stop the paging response timer and establish the CS connection, then the MT call process as described in detail in TS 23.018 [5].
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7.7.3 Void
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7.8 Mobile Terminating Call when SGs is not active
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Regular pre-Release 8 MSC procedures are performed without any ISR or SGs specifics.
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8 Other CS Services
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8.1 General
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The MSC handles the timers, queuing and retransmission for sending the SGsAP-PAGING-REQUEST message on the SGs interface in the same way that it handles the sending of a PAGING message on the A or Iu interface. As a consequence, the MME and (if ISR is active) the SGSN shall not implement local retransmission schemes for this paging.
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8.2 Short Message Service (SMS)
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8.2.1 General
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The procedures for SMS in this specification apply only if the UE is EPS/IMSI attached and the Non Access Stratum signalling based SMS transfer is chosen by the UE and/or the home PLMN for delivering short messages.
This clause describes both the mobile originating and mobile terminating SMS over SGs procedures in EPS. SMS support is based on the connectionless SGs reference point between the MME and the MSC Server and use of NAS signalling between the UE and the MME, i.e. no CS Fallback is performed for SMS.
This clause also describes the SMS procedures between the UE and the MME for UEs that use only PS and SMS services but no CS Fallback via GERAN and/or UTRAN.
The SMS protocol entities are reused from the existing MS/UE and MSC implementations. This means that the SMS over SGs procedures reuse the different protocol layers as defined in TS 23.040 [14].
NOTE. With SMS over SGs, the MSC/VLR produces the Call Detail Record. The stage 3 changes to the CDR for SMS over SGs were made in a manner that should permit an unmodified Release 7 entity to receive the CDR. However, for correct operation of, e.g. customer care services, when using an unmodified Release 7 entity to receive the CDR, the VPLMN should ensure that the TAC values do not overlap with the LAC values.
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8.2.2 Mobile originating SMS in Idle Mode
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The following sequence flow shows the delivery of mobile originating SMS in idle mode. The message flows between the ME/UE and MSC/VLR are also broadly applicable to the Memory Available Notification.
Figure 8.2.2-1: Mobile originating SMS in idle mode
1. The combined EPS/IMSI attach procedure as described in clause 5.2 has been performed earlier.
2. A mobile originating SMS is triggered and the MS/UE is in idle mode. The MS/UE initiates the UE triggered Service Request procedure, which is defined in TS 23.401 [2]. The UE indicates its S‑TMSI in the RRC signalling. If the UE and the MME accept to use Control Plane CIoT EPS Optimisation, then to enable SMS transfer the Service Request procedures defined in TS 23.401 [2] are not used for MO SMS, but instead UE and MME shall be using Control Plane CIoT EPS Optimisation.
For E-UTRAN, if there is a Service Gap timer running in the MME for the UE and the MME is not waiting for a MT paging response from the UE, the MME rejects the Service Request by discarding any NAS data PDU and sending a Service Reject message to the UE with an appropriate cause. The MME may also provide UE with a Mobility Management Back-off timer set to the remaining value of Service Gap timer (see TS 23.401 [2], clause 4.3.17.9).
NOTE 1: The above Service Gap enforcement is for UEs that do not support Service Gap Control. UEs that do support Service Gap Control will not invoke this procedure when the Service Gap timer is running in the UE.
3. The MS/UE builds the SMS message to be sent as defined in TS 23.040 [14] (i.e. the SMS message consists of CP-DATA/RP-DATA/TPDU/SMS-SUBMIT parts). Following the activation of the Radio Bearers, the SMS message is encapsulated in an NAS message and sent to the MME.
4. The MME forwards the SMS message to the MSC/VLR in an Uplink Unitdata message. In order to permit the MSC to create an accurate charging record, the MME adds the IMEISV, the local time zone, the Mobile Station Classmark 2, and the UE's current TAI and E‑CGI.
4a. The MSC/VLR acknowledges receipt of the SMS to the UE.
5.-8. These steps are performed as defined in TS 23.040 [14]. The SMS message is forwarded to the SC that returns a delivery report message.
9. The MSC/VLR forwards the received delivery report to the MME associated with the MS/UE in a Downlink Unitdata message.
10. The MME encapsulates the received delivery report in an NAS message and sends the message to the MS/UE.
11, 12. The UE acknowledges receipt of the delivery report to the MSC/VLR.
13. The MSC/VLR indicates to the MME that no more NAS messages need to be tunnelled.
The MME should not use the SGs Release Request message as a trigger for the release of S1 resources.
NOTE 2: This is because the MME does not know whether the Service Request performed in step 2 was solely for the purpose of SMS, or, was for SMS and user plane data, or, whether or not the mobile has additional SMSs to send.
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8.2.3 Mobile originating SMS in Active Mode
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Mobile Originating SMS in active Mode procedure is specified by reusing the Mobile Originating SMS in Idle Mode with the following modification:
- The established signalling connection between the MS/UE and the MME is reused for the transport of the SMS message and the delivery report (i.e. the UE triggered Service Request procedure defined in step 2 is skipped).
8.2.3a Multiple Mobile originating SMSs
In clause 3.2 of TS 24.011 [28], the simultaneous transmission of more than one MO SMS/notification per domain is prohibited.
If the UE has more than one SMS/notification to send, the subsequent SMS/notification is sent at step 11 of clause 8.2.2 and the acknowledgement of the delivery report for the previous SMS/notification is not sent.
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8.2.4 Mobile terminating SMS in idle mode
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The following sequence flow shows the delivery of mobile terminating SMS in idle mode.
Figure 8.2.4-1: Mobile terminating SMS in idle mode
1. The combined EPS/IMSI attach procedure as described in clause 5.2 has been performed.
2‑4. The SC initiates transfer of mobile terminating SMS. The HLR is requested for routing number for SMS services and the SMS message is forwarded to the MSC/VLR where the MS/UE is CS attached.
5. The MSC/VLR sends a Paging (IMSI, VLR TMSI, Location Information, SMS indicator) message to the MME.
6. The MME initiates the paging procedure by sending the Paging (as specified in TS 23.401 [2]) message to each eNodeB with cells belonging to the tracking area(s) in which the UE is registered. The UE is paged with its S‑TMSI.
7. The MS/UE is paged by the eNodeBs.
8. The UE sends a Service Request message to the MME. The UE indicates its S‑TMSI in the RRC signalling. The MME sends the S1-AP Initial Context Setup Request message to the eNodeB and the eNodeB establishes the Radio Bearers. If the UE and the MME accept to use Control Plane CIoT EPS Optimisation, then to enable SMS transfer the Service Request procedures defined in TS 23.401 [2] are not used, but instead UE and MME shall be using the Control Plane CIoT EPS Optimisation.
8a. The MME sends a Service Request message to the MSC. In order to permit the MSC to create an accurate charging record, the MME adds the IMEISV, the local time zone, the Mobile Station Classmark 2, and the UE's current TAI and E‑CGI.
9a. The MSC/VLR builds the SMS message to be sent as defined in TS 23.040 [14] (i.e. the SMS message consists of CP‑DATA/RP‑DATA/TPDU/SMS‑DELIVER parts). The MSC/VLR forwards the SMS message to the MME in a Downlink Unitdata message.
9b. The MME encapsulates the SMS message in a NAS message and sends the message to the MS/UE.
9c, 9d. The MS/UE acknowledges receipt of the SMS message to the MSC/VLR.
10. The MS/UE returns a delivery report as defined in TS 23.040 [14]. The delivery report is encapsulated in an NAS message and sent to the MME.
11. The MME forwards the delivery report to the MSC/VLR in an Uplink Unitdata message.
12‑13. These steps are performed as defined in TS 23.040 [14]. The delivery report is forwarded to the SC.
14-15. In parallel to steps 12-13, the MSC/VLR acknowledges receipt of the delivery report to the MS/UE.
16. The MSC/VLR indicates to the MME that no more NAS messages need to be tunnelled.
The MME should not use the SGs Release Request message as a trigger for the release of S1 resources.
NOTE: Although the MME could use the RRC establishment cause (set to mt-Access) sent in the S1-AP Initial UE Message in step 8 to deduce that the MS/UE sent the Service Request solely for receiving the SMS), the MME does not know whether the MT-SMS might cause the initiation of user plane traffic or an MO SMS. So, for simplicity of MME implementation, the normal eNodeB procedures should be used to initiate the release of S1 resources.
8.2.4a Mobile Terminated SMS in extended Idle mode DRX and in PSM
8.2.4a.1 General
Mobile terminated SMS in extended idle mode DRX or in PSM can be achieved via different deployment options depending on operator needs:
- Deployment Option 1:
- Based on MME rejection of paging message from MSC/VLR with no impact to SMS-GMSC.
- Deployment Option 2:
- Based on deployment Option 1, with additional optimization for avoiding additional signalling to HLR/HSS, consisting on signalling and handling of Maximum Retransmission Time.
- Deployment Option 3:
- The supervision timers to acknowledge receipt of the SMS message at the SMS-GMSC and at the MSC/VLR may be configured by the operator with a value (e.g. 45 minutes) longer than the maximum possible extended idle mode DRX cycle allowed in the network and the maximum possible time that the network allows the UE to continue to remain in power saving state.
8.2.4a.2 Procedure for Deployment Option1 and Deployment Option 2
The sequence flow described in Figure 8.2.4a.2-1 shows the delivery of mobile terminating SMS when the UE is using extended idle mode DRX with a DRX cycle value, or when the UE is in Power Saving Mode (as defined in TS 23.682 [48]) that can cause mobile terminating SMS retransmissions for Deployment Option 1. It also shows the additional optimizations in case of Deployment Option 2.
Figure 8.2.4a.2-1: Mobile terminating SMS in extended idle mode DRX (Deployment Options 1 and 2)
1. The combined EPS/IMSI attach procedure as described in clause 5.2 has been performed, and extended Idle mode DRX has been negotiated.
2 4. The SC initiates transfer of mobile terminating SMS. The HLR is requested for routing number for SMS services and the SMS message is forwarded to the MSC/VLR where the MS/UE is CS attached. The SMS-GMSC may include in case of Deployment Option 2 the Maximum Retransmission Time in the Forward Short Message to indicate that it is capable to retransmit the Short Message until a maximum retransmission time.
5. The MSC/VLR sends a Paging (IMSI, VLR TMSI, Location Information, SMS indicator, in Deployment Option 2, SM Delivery Timer, SM Delivery Start Time) message to the MME. For Deployment Option 2, if the Forward Short Message received from the SMS-GMSC includes the Maximum Retransmission Time IE, the VLR should forward the received Maximum Retransmission Time IE in the Paging message to indicate to the MME that the SMS GMSC is capable to retransmit the Short Message until the indicated maximum retransmission time. In Deployment Option 2, if the Forward Short Message received from the SMS-GMSC includes the SM Delivery Timer and SM Delivery Start Time IEs, the VLR may include these IEs in the Paging message to indicate to the MME the time until which the VLR supports buffering the Short Message.
6a. If the UE is considered unreachable for paging (as specified in TS 23.682 [48]), the MME sends UE unreachable message (cause that indicates UE Temporarily Unreachable and for Deployment Option 2 Requested Retransmission Time, SM Buffer Request Indicator) to the MSC/VLR.
For UEs using extended idle mode DRX, the MME proceeds with step 6a, steps 6b-14 as shown in Figure 8.2.4a.2-1 and described below are performed.
For UEs in Power Saving Mode, the MME proceeds with step 6a, steps 7a-9, and steps 11-14 as shown in Figure 8.2.4a.2-1 and described below are performed.
For Deployment Option 2, if the UE is using a power saving mechanism such as extended idle mode DRX or Power Saving Mode and the Paging message includes the Maximum Retransmission Time IEs, the MME may return an UE Unreachable message to that VLR with the cause UE Temporarily Unreachable and with the Requested Retransmission Time IE requesting the SMS GMSC to retransmit the Short Message at a later time prior to the Maximum Retransmission Time. In that case, the MME shall set the NEAF, so as to notify the VLR of any subsequent UE activity prior to the requested SM retransmission time.
In Deployment Option 2, if the UE is using extended idle mode DRX or PSM and the Paging message includes the SM Delivery Timer and SM Delivery Start Time IEs, and if the UE is expected to respond to paging after the paging guard timer but before the time indicated by the SM-Delivery-Timer and SM-Delivery-Start-Time IEs, the MME should page the UE and return an UE Unreachable message to that VLR with cause UE Temporarily Unreachable and with the SM Buffer Request Indicator to request the VLR to buffer the Short Message.
In Deployment Option 2, if the VLR included the SM-Delivery-Timer and SM-Delivery-Start-Time IEs in the Paging message, and if the UE Unreachable message indicates a request to buffer the Short Message in the VLR, the VLR shall buffer the Short Message until the time indicated in the Paging message or until receipt of any earlier SGs Service Request message. Steps 7a-9 and 12-14 are not performed.
Otherwise, if the UE is considered reachable for paging, steps 6-16 of clause 8.2.4 are performed.
6b. The MME sends the paging request just before the occurrence of next paging occasion. This step is not performed for UEs in PSM.
NOTE: Steps 7-9 are as per legacy behaviour of MT SMS delivery failure as defined in TS 23.040 [14].
7. The MSC/VLR sends a failure report to the SMSC-GMSC with an Absent Subscriber indication as defined in TS 23.040 [14]. For Deployment Option 2, if the UE Unreachable message includes the Requested Retransmission Time IE, the VLR shall forward the received Requested Retransmission Time IE in the Failure Report to the SMS-GMSC. In that case, the MSC/VLR shall not set the MNRF flag, and steps 8-9 and 12-13 are not performed.
7a. The MSC/VLR shall, in parallel with step 8, set its MNRF and send an SGs interface Alert Request message to the MME, as described in clause 8.2.5c. The MME shall set the NEAF so as to notify the MSC/VLR of any subsequent UE activity.
8. When the SMS-GMSC receives the absent subscriber indication from MSC/VLR it sends an SM-DeliveryReportStatus with absent subscriber indication to HSS in order to be notified when the UE becomes reachable, according to TS 23.040 [14].
9. The SMS-GMSC, in parallel with step 8, sends a failure report to the SC, according to TS 23.040 [14].
10. The MS/UE is paged by the eNodeBs. This step is not performed for UEs in PSM.
11. The UE sends a Service Request message to the MME. The UE indicates its S-TMSI in the RRC signalling. The MME sends the S1-AP Initial Context Setup Request message to the eNodeB and the eNodeB establishes the Radio Bearers. The network should ensure the UE is connected long enough that it allows the SC to reattempt to deliver the MT SMS message while the UE is still active. If the UE and the MME accept to use Control Plane CIoT EPS Optimisation, then to enable SMS transfer, the Service Request procedures defined in TS 23.401 [2] are not used, but instead UE and MME shall use Control Plane CIoT EPS Optimisation procedure defined in TS 23.401 [2].
For UEs in PSM, Service Request, or Data Transport in Control Plane CIoT EPS Optimisation or Tracking Area Update, as defined TS 23.401 [2], is performed when the UE wakes up from its power saving state.
12. The MME sends UE-Activity-Indication (IMSI) to the MSC/VLR. For Deployment Option 2, if the UE is using a power saving mechanism (such as extended idle mode DRX or PSM), the MME includes the Maximum UE Availability Time IE in the UE-Activity-Indication message to indicate the time until which the UE is expected to be reachable.
12a. The MSC/VLR sends Ready-For-SM Service to the HLR. For Deployment Option 2, the MSC/VLR includes this information to the HLR if received in step 12.
13. The HLR initiates Alert-SC function towards the SC as defined in TS 23.040 [14]. For Deployment Option 2, the HLR includes the Maximum UE Availability Time IE in the Alert-SC if received at step 12a.
14. The SC initiates a new attempt to deliver the MT SMS according to clause 8.2.5. For Deployment Option 2, the SC prioritizes the retransmission of pending Mobile Terminated Short Messages to UEs using a power saving mechanism, i.e. UEs known to have a Maximum UE Availability Time.
8.2.4a.3 Procedure for Deployment Option 3
The following sequence flow described in Figure 8.2.4a.3-1 shows the delivery of mobile terminating SMS when the UE is using extended idle mode DRX (as defined in TS 23.682 [48]) with a DRX cycle value, or when the UE is using PSM, that can cause mobile terminating SMS retransmissions for Deployment Option 3.
Figure 8.2.4a.3-1: Mobile terminating SMS in extended idle mode DRX (Deployment Option 3)
1-5. Steps 1-5 as described in clause 8.2.4 are performed.
6a. If the UE is considered unreachable for paging due to using extended idle mode DRX or PSM (as specified in TS 23.682 [48]), the MME sends a Service Request message to the MSC/VLR. If the MME proceeds with step 6a, steps 6b-16 as shown in Figure 8.2.4a.3-1 and described below are performed.
Otherwise steps 6-16 of clause 8.2.4 are performed.
6b. The MSC/VLR builds the SMS message to be sent as defined in TS 23.040 [14] (i.e. the SMS message consists of CP DATA/RP DATA/TPDU/SMS DELIVER parts). The MSC/VLR forwards the SMS message to the MME in a Downlink Unitdata message. The MME stores the received SMS message.
7a. The MME sends the paging request just before the occurrence of next paging occasion. This step is not performed for UEs in PSM.
7b. The MS/UE is paged by the eNodeBs. This step is not performed for UEs in PSM.
8. The UE sends a Service Request message to the MME. The UE indicates its S TMSI in the RRC signalling. The MME sends the S1-AP Initial Context Setup Request message to the eNodeB and the eNodeB establishes the Radio Bearers. If the UE and the MME accept to use Control Plane CIoT EPS Optimisation, then to enable SMS transfer the Service Request procedures defined in TS 23.401 [2] are not used, but instead UE and MME shall use Data Transport in Control Plane CIoT EPS Optimisation procedure defined in TS 23.401 [2].
For UEs in PSM, Service Request, or Data Transport in Control Plane CIoT EPS Optimisation or Tracking Area Update, as defined TS 23.401 [2] is performed when the UE wakes up from its power saving state.
9. The MME encapsulates the SMS message in a NAS message and sends the message to the MS/UE.
9c-16. Steps 9c-16 as described in clause 8.2.4 are performed.
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8.2.5 Mobile terminating SMS in Active Mode
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Mobile terminating SMS in Active Mode procedure is specified by reusing the Mobile Terminating SMS in Idle Mode with the following modification:
- There is no need for the MME to perform Paging of the MS/UE after step 5. MME continues with step 8a (i.e. steps 6 to 8 are skipped). The MME immediately sends a Downlink Unitdata to the UE.
- The MME also includes the E-CGI and TAI in step 9d.
8.2.5a Multiple Mobile terminating SMSs
In clause 3.2 of TS 24.011 [28], the simultaneous transmission of more than one MT SMS per domain is prohibited.
If the MSC/VLR has more than one SMS to send, the subsequent SMS is sent in a Downlink Unitdata message after step 14 and instead of the Release Request in step 16 of clause 8.2.4. i.e. the MSC/VLR does not need to send another SGs Paging message.
8.2.5b Simultaneous Mobile terminating and Mobile originating SMSs
The above clauses on mobile originating and mobile terminating SMS handling in active and idle mode can be reused such that no special treatment is needed for this case.
8.2.5c Unsuccessful Mobile terminating SMS delivery attempt
As specified in clause 3.2.8 of TS 23.040 [14], setting the Mobile Station Not Reachable Flag (MNRF) in the MSC/VLR is mandatory. However, when using the SGs interface, the MSC/VLR has delegated the 'implicit detach' functionality to the MME (and/or, if Network Mode of Operation 1 is in use in GERAN/UTRAN, to the SGSN).
If an SGs based MT SMS delivery attempt fails, the MSC/VLR shall set its MNRF and send an SGs interface Alert Request message to the MME. Upon receipt of Alert Request message, MME shall set its Non-EPS Alert Flag (NEAF) and if ISR is activated, the MME shall then send an S3 interface Alert-MME-Request message to the SGSN. SGSN shall set the S3 SMS Alert Flag (SSAF).
If the MME operator knows (e.g. because it is in the HPLMN) that the receiving UE's HPLMN deploys SMS-Router, and if the receiving UE's HPLMN uses both SMS via MSC and SMS via SGSN, then the MME need not send the Alert-MME-Request message to the SGSN for that UE.
NOTE: The receiving UE's HPLMN should ensure that the SMS-Router in the receiving UE's HPLMN only returns SMS-Router address to the SMS-GMSC of the sender UE's PLMN.
Subsequently, if the UE makes radio contact with the SGSN and SSAF is set, the SGSN informs the MME with an S3 interface UE-Activity-Indication. Upon receipt of the S3 interface UE-Activity-Indication, or, if the UE makes radio contact with the MME, the MME sends an SGs AP UE-Activity-Indication message to the MSC/VLR. Upon receipt of an SGs AP UE-Activity-Indication message, or signalling on the A, Iu-cs or Gs interface for that UE, the MSC/VLR shall inform the HLR.
For Deployment Option 2, if the UE is using a power saving mechanism (such as extended idle mode DRX), the MME may include the Maximum UE Availability Time IE in the SGs AP UE-Activity-Indication message to indicate the time until which the UE is expected to be reachable. This information may be used by the SMS Service Centre to prioritize the retransmission of pending Mobile Terminated Short Messages to UEs using a power saving mechanism.
8.2.5d Non-SMS Mobile terminating activity during SMS delivery
While one or more SMS is being transferred, other mobile terminating requests (e.g. an MT voice call) may arrive in the MSC/VLR. If this happens the MSC/VLR continues the SMS activities but shall also send the SGs Paging message for the non-SMS activity to the MME. The MME shall handle this SGs Paging message as if no SMS transfers are ongoing. Typically this should lead to the MME invoking the handover/call redirection to GERAN/UTRAN features and it may lead to disruption of the SMS delivery. The MSC/VLR and UE shall recover from any such SMS disruption using the normal RP and CP layer retransmission timers/mechanisms.
8.2.5e Non-SMS Mobile originating activity during SMS delivery
While one or more SMS is being transferred, other mobile originating requests (e.g. an MO voice call or USSD) may be requested by the user. If this happens the MS/UE continues the SMS activities but shall also send the Extended Service Request message for the non-SMS activity to the MME. The MME shall handle this Extended Service Request message as if no SMS transfers are ongoing. Typically this should lead to the MME invoking the handover/call redirection to GERAN/UTRAN features and it may lead to disruption of the SMS delivery. The MSC/VLR and UE shall recover from any such SMS disruption using the normal RP and CP layer retransmission timers/mechanisms.
8.2.5f Mobile Terminating SMS when ISR is active and SGs is active between MSC/VLR and MME
When the MME receives the SGs Paging message for SMS, and ISR is active, and the UE is in idle mode, the MME sends the S1 interface paging message to the E‑UTRAN (using the S-TMSI as temporary identity) and sends a CS paging message (SMS indicator) to the SGSN using the MSC TMSI as temporary identity (unless the MSC did not allocate a TMSI, in which case the IMSI is used for paging).
The UE is paged on E‑UTRAN and by the SGSN on GERAN and/or UTRAN. For GERAN A/Gb mode, the SGSN sends a PAGING CS message to the BSS (see TS 48.018 [30]) if "SMS in SGSN" is not used for this UE. For UTRAN, the SGSN sends a PAGING message to the UTRAN (see TS 25.413 [29]) with the CN Domain Indicator set to 'CS domain' and the Paging Cause set to 'Terminating Low Priority Signalling' if "SMS in SGSN" is not used for this UE. The UE responds on the cell on which it is camped. When camped on E-UTRAN, the UE responds to the MME. When camped on GERAN or UTRAN, the UE responds to the MSC.
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8.2.6 Co-Existence with SMS over generic 3GPP IP access
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If the home operator has deployed SMS over generic 3GPP IP access and/or SMS-Instant Messaging Interworking as defined in TS 23.204 [15], and has configured the network and the UE for using SMS over IP or SMS-Instant Messaging Interworking, then an SMS or IM will be delivered over EPS in any visited network whether or not the visited network supports SMS over generic 3GPP IP access.
If the home operator has not deployed SMS over generic 3GPP IP access and the UE fails to successfully complete the combined EPS/IMSI attach procedure in the visited network (i.e. the visited network supports SMS over generic 3GPP IP access and does not support SGs for SMS capability), then the UE cannot execute MT or MO SMS procedures in the visited network.
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8.3 Location Services (LCS)
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8.3.1 MO-LR procedure
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8.3.1.1 General
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MO-LR procedure in the CS fallback in EPS is performed as specified in TS 23.271 [8].
When the MO-LR procedure is triggered by the UE's application, UE will check the LCS Support Indication provided by the Attach and TAU procedures as specified in TS 23.401 [2]:
- If the LCS Support Indication indicates EPC-MO-LR is supported, and if the UE supports EPC-MO-LR, the UE stays in LTE and initiates the EPC-MO-LR procedure.
- If EPC-MO-LR is not supported by either the network or the UE and if the LCS Support Indication indicates CS-MO-LR is supported, and the UE supports CS-MO-LR, the UE assumes CS-MO-LR is provided. Also, if EPC-MO-LR is not supported by either the network or the UE and if network does not provide information on whether CS-MO-LR is supported, then UE assumes CS-MO-LR may be provided. In these cases, if the previous combined EPS/IMSI Attach or Combined TA/LA Update is accepted with no "SMS only" indication, then the UE initiates CS Fallback to perform CS-MO-LR.
NOTE: Based on UE implementation, UE may avoid initiating CS-MO-LR when an IMS VoIP session is active.
- Otherwise, the UE shall not attempt the EPC-MO-LR procedure, i.e. neither EPC-MO-LR nor CS-MO-LR with CS Fallback.
If the UE decided to initiate the CS Fallback for the LCS based on LCS Support Indication check, then, the following applies:
- When the UE is in active mode without an IMS VoIP session, the UE and the network follow the procedure in clause 6.2 "Mobile Originating Call in Active Mode - PS HO supported" or clause 6.3 "Mobile Originating call in Active Mode - No PS HO supported". After the UE changes its RAT from E-UTRAN to UTRAN/GERAN, it performs CS-MO-LR procedures as specified in TS 23.271 [8].
- When the UE is in active mode with an IMS VoIP session and if the UE supports SRVCC procedures, the UE and the network follow the procedure in clause 8.3.1.2 "MO-LR in Active Mode with IMS VoIP session - PS HO supported".
- When the UE is in active mode without an IMS VoIP session but the network decides not to perform PS-Handover, then the UE and the network follow the procedure in clause 6.3 "Mobile Originating Call in Active Mode - No PS HO Support". After the UE changes its RAT from E-UTRAN to UTRAN/GERAN, it performs CS-MO-LR procedure as specified in TS 23.271 [8].
- When the UE is in active mode with an IMS VoIP session and if the UE supports SRVCC procedures but the network decides not to perform PS-Handover, then the UE and the network follow the procedure in clause 8.3.1.3 "MO-LR in Active Mode with IMS VoIP session – No PS HO supported".
- When UE is in idle mode, UE follows the procedure in clause 6.4 "Mobile Originating Call in Idle Mode". After UE changes its RAT from E-UTRAN to UTRAN/GERAN, it performs CS-MO-LR procedure as specified in TS 23.271 [8].
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8.3.1.2 MO-LR in Active Mode with IMS VoIP session - PS HO supported
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Figure 8.3.1.2-1: MO-LR Request in E-UTRAN while UE is in IMS VoIP session
1a.-2. These steps are performed as defined in clause 6.2.
3. Based on UE measurement reports and CS Fallback Indicator in step 1b, the source E‑UTRAN decides to trigger an SRVCC handover to UTRAN/GERAN. Continuous SRVCC procedures are continued as specified in TS 23.216 [20], clause 6.2.2.2.
4. After sending a Handover Complete message via the RNS/BSS to the MSC in step 3, the UE sends a CM Service Request to the MSC indicating a request for location services. After the HLR is updated and the subscriber data are downloaded from the HLR, the MSC sends a CM Service Accept to the UE. Then the UE sends a NAS MO-LR Request to the MSC.
5. Continuation of MO-LR procedures as specified in TS 23.271 [8], clause 9.2.6.
When SRVCC capable UE is in active mode with an IMS VoIP session but the network does not support SRVCC, MME sends a Service Reject in response to step 1a based on EPS bearer information, i.e. MME rejects the request if UE has EPS bearer with QCI=1, i.e. IMS VoIP session.
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8.3.1.3 MO-LR in Active Mode with IMS VoIP session - No PS HO supported
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The same procedure as described in clause 8.3.1.2 applies for "MO-LR in Active Mode with IMS VoIP session - No PS HO supported" case except that the SRVCC procedure in step 3 follows TS 23.216 [20], clause 6.2.2.1a.
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8.3.2 MT-LR procedure
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8.3.2.1 MT-LR procedure if UE is not in IMS VoIP session
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Figure 8.3.2.1-1: MT-LR procedure if UE is not in IMS VoIP session
1. MSC receives a PROVIDE_SUBSCRIBER_LOCATION message due to CS‑MT‑LR (TS 23.271 [8], clause 9.1.2).
2. MSC sends Paging (LCS Client Identity, LCS indicator) message to MME.
3. If the MME did not return the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME sends Paging (parameters as specified in TS 23.401 [2], CN Domain Indicator, LCS Client Identity, LCS indicator) message to UE. LCS indicator is used to inform the UE that this paging if for MT-LR request. LCS Client Identity and LCS indicator are only included in CS Page if UE is in active mode.
If the MME returned the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME shall not send Paging to the UE, and the MME sends CS Paging Reject towards MSC to stop CS Paging procedure and this CSFB procedure stops.
4. UE responds with Paging_Resp message in UMTS/GERAN. Service based redirection/reselection or PS Handover may take place as specified in clause 7.
5. MSC continues with the CS‑MT‑LR procedure as defined in TS 23.271 [8], clause 9.1.2.
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8.3.2.2 MT-LR procedure while UE is in IMS VoIP session
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Figure 8.3.2.2-1: MT-LR procedure while UE is in IMS VoIP session
1. MSC receives a PROVIDE_SUBSCRIBER_LOCATION message due to CS MT LR (TS 23.271 [8], clause 9.1.2).
1a. The MSC responds by sending a Paging Request (LCS Client Identity, LCS indicator) to the MME over a SGs interface. The MSC only sends a CS Page for an UE that provides location update information using the SGs interface. The MME has an established S1 connection for IMS VoIP session.
If the MME did not return the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME sends Paging (parameters as specified in TS 23.401 [2], CN Domain Indicator, LCS Client Identity, LCS indicator) message to UE. LCS indicator is used to inform the UE that this paging is for MT-LR request.
If the MME returned the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME shall not send Paging to the UE, and the MME sends CS Paging Reject towards MSC to stop CS Paging procedure and this CSFB procedure stops.
The eNodeB forwards the paging message to the UE.
1b. UE sends an Extended Service Request (Reject or Accept) message to the MME for mobile terminating CS Fallback. The Extended Service Request message is encapsulated in RRC and S1-AP messages. The UE may decide to reject CSFB based on LCS Client Identity.
1c. Upon receiving the Extended Service Request (Reject) for mobile terminating CS Fallback, the MME sends Paging Reject towards MSC to stop CS Paging procedure and this CSFB procedure stops. Corresponding error handling is returned to the GMLC as specified in TS 23.271 [8].
1d. MME sends an S1-AP Request message to eNodeB that includes the UE Radio Capabilities and a CS Fallback Indicator. This message: indicates to the eNodeB that the UE should be moved to UTRAN/GERAN.
1e. The eNodeB shall reply with S1-AP Response message.
2. These steps are performed as defined in clause 7.3 for PS handover supported case and clause 7.4 for No PS handover supported case.
3. Based on UE measurement reports and CS Fallback Indicator in step 1d, the source E‑UTRAN decides to trigger an SRVCC handover to UTRAN/GERAN. Continuous SRVCC procedures as specified in TS 23.216 [20], clause 6.2.2.2 for PS handover supported case and clause 6.2.2.1a for No PS HO supported case are performed.
4. After receiving Relocation/Handover Complete message from the RNS/BSS in step 3, MSC sends LCS Location Notification Invoke to the UE.
5. Continuation of CS-MT-LR procedures as specified in TS 23.271 [8], clause 9.1.2.
When SRVCC capable UE is in active mode with an IMS VoIP session but the network does not support SRVCC, MME sends Paging Reject towards MSC and this CSFB procedure stops. This is based on the bearer information at MME indicating UE has IMS VoIP session, i.e. EPS bearer with QCI=1.Corresponding error handling is returned to the GMLC as specified in TS 23.271 [8].
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8.3.3 NI-LR procedure
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NI-LR procedure takes place during emergency calls, and is thus performed in GERAN/UTRAN during the Mobile Originating call procedure.
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8.3.4 Returning back to E-UTRAN
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Once CS service ends in CS domain, existing mechanisms as specified in TS 23.401 [2] can be used to move the UE to E-UTRAN, no specific CS Fallback mechanisms are needed.
During the release of an RR connection the MSC should indicate to GERAN/UTRAN that the RR connection (for call or CISS or LCS) was established as a result of CS fallback. GERAN and UTRAN may use the indication to determine which of the existing mechanisms that should be used to move the UE to E‑UTRAN.
When configured to support the return to the last used PLMN after CSFB, after a successful setup of an RR connection or during the release of the UTRAN RR connection, the MSC shall further indicate to GERAN/UTRAN the last used LTE PLMN ID. GERAN and UTRAN shall take the last used LTE PLMN ID into account when selecting the target cell in PS handover to E-UTRAN or when selecting the dedicated target frequency list for idle mode mobility to E-UTRAN in RR Connection Release procedure.
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8.3.5 Co-Existence with Other Location Services
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8.3.5.1 Co-Existence with SUPL
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There is no race condition between OMA AD SUPL [9] and CS Fallback for LCS. When network initiated SUPL procedure takes place, the paging message does not contain CN Domain Indicator by default. This prevents CS Fallback for LCS to take place. For SET initiated SUPL procedure, changing of RAT does not take place.
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8.4 Other CS Services
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8.4.0 General
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The procedures specified in this clause apply when the UE is EPS/IMSI attached and the CS domain is chosen by the UE and/or the home PLMN to deliver other types of CS services, i.e. services not covered explicitly in previous clauses, such as Call Independent Supplementary Services, real time end-to-end facsimile group 3 services, TS 23.146 [41], etc.
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8.4.1 Mobile-Initiated CS Services
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8.4.1.1 Mobile-Initiated CS Services if UE is not in IMS VoIP session
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When UE is in active mode, UE and the network follow the procedure in clause 6.2 "Mobile Originating Call in Active‑Mode". After UE changes its RAT from E‑UTRAN to UTRAN/GERAN, it performs Mobile‑Initiated CS procedures relevant to the initiated CS service, e.g. Call Independent Supplementary Service procedure as specified in TS 24.010 [13], real time end-to-end facsimile group 3 procedure as specified in TS 23.146 [41], etc.
When UE is in active mode and network initiates NACC procedure, then UE and the network follow the procedure in clause 6.3 "Mobile Originating Call in Active Mode ‑ No PS HO Support in GERAN". After UE changes its RAT from E‑UTRAN to UTRAN/GERAN, it performs Mobile-Initiated CS procedures relevant to the initiated CS service, e.g. Supplementary Service procedure as specified in TS 24.010 [13], real time end-to-end facsimile group 3 procedure as specified in TS 23.146 [41], etc.
When UE is in idle mode, UE and the network follows the procedure in clause 6.4. After UE changes its RAT from E‑UTRAN to UTRAN/GERAN, it performs Mobile-Initiated CS procedures relevant to the initiated CS service, e.g. Supplementary Services procedure as specified in specifications such as TS 23.090 [10], real time end-to-end facsimile group 3 procedure as specified in TS 23.146 [41], etc.
MSC may set a timer upon reception of the Call Independent Supplementary Service operation and maintain the RRC connection until the timer expires. Upon reception of a subsequent CISS operation the timer is re-set. This reduces the risk that the UE is returned to the E-UTRAN and then back to UTRAN/GERAN for each subsequent CISS operation.
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8.4.1.2 Mobile-Initiated CS Services while UE is in IMS VoIP session
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When the UE is in active mode with an IMS VoIP session and if the UE supports SRVCC procedures, the procedure for Mobile-Initiated CS Services while UE is in IMS VoIP session is the same as for "NW-Initiated CS Services while UE is in IMS VoIP session" in clause 8.4.2.2 from step 1b (Extended Service Request), with the difference that the Extended Service Request is for mobile originating CS Fallback.
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8.4.2 NW-Initiated CS Services
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8.4.2.1 NW-Initiated CS Services if UE is not in IMS VoIP session
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Figure 8.4.2.1-1: NW-Initiated CS Service procedure
1. MSC/VLR receives a trigger for a NW-Initiated CS procedure.
2. MSC/VLR sends Paging message to MME. For call independent supplementary service, the Paging message may include the SS service ID.
3. If the MME did not return the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME sends Paging (parameters as specified in TS 23.401 [2], CN Domain Indicator) message to UE. For call independent supplementary service the Paging message may include the SS service ID. SS service ID is used to indicate that a call independent supplementary service is triggered. The SS service ID is only included in CS Page if UE is in active mode.
If the MME returned the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME shall not send the Paging to the UE, and the MME sends CS Paging Reject towards MSC to stop CS Paging procedure and this CSFB procedure stops.
4. The mobile terminating call procedure then takes place as specified in clause 7 "Mobile Terminating Call Procedure".
5. Once the paging is successfully returned to MSC, the applicable CS procedures continues, e.g. for Supplementary Service as specified in specifications such as TS 23.090 [10].
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8.4.2.2 NW-Initiated CS Services while UE is in IMS VoIP session
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Figure 8.4.2.2-1: NW-Initiated CS Service procedure while UE is in IMS VoIP session
1. MSC/VLR receives a trigger for a NW-Initiated CS procedure.
1a. The MSC responds by sending a Paging Request to the MME over a SGs interface. For call independent supplementary service, the Paging message may include the SS service ID. The MME has an established S1 connection for IMS VoIP session.
If the MME did not return the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME sends Paging (parameters as specified in TS 23.401 [2], CN Domain Indicator) message to UE. For call independent supplementary service the Paging message may include the SS service ID. SS service ID is used to indicate the type of the supplementary service to the UE. The SS service ID is only included in CS Page if UE is in active mode.
If the MME returned the "SMS-only" indication to the UE during Attach or Combined TA/LA Update procedures, the MME shall not send the Paging to the UE, and the MME sends CS Paging Reject towards MSC to stop CS Paging procedure and this CSFB procedure stops.
The eNodeB forwards the paging message to the UE.
1b. UE sends an Extended Service Request (Reject or Accept) message to the MME for mobile terminating CS Fallback. The Extended Service Request message is encapsulated in RRC and S1-AP messages.
1c. Upon receiving the Extended Service Request (Reject) for mobile terminating CS Fallback, the MME sends Paging Reject towards MSC to stop CS Paging procedure and this CSFB procedure stops. Corresponding error handling is returned to the GMLC as specified in TS 23.271 [8].
1d. MME sends an S1-AP Request message to eNodeB that includes the UE Radio Capabilities and a CS Fallback Indicator. This message indicates to the eNodeB that the UE should be moved to UTRAN/GERAN.
1e. The eNodeB shall reply with S1-AP Response message.
2. These steps are performed as defined in clause 7.3 for PS handover supported case and clause 7.4 for No PS handover supported case.
3. Based on UE measurement reports and CS Fallback Indicator in step 1d, the source E‑UTRAN decides to trigger an SRVCC handover to UTRAN/GERAN. Continuous SRVCC procedures as specified in TS 23.216 [20], clause 6.2.2.2 for PS handover supported case and clause 6.2.2.1a for No PS HO supported case are performed.
4. After receiving Relocation/Handover Complete message from the RNS/BSS in step 3, the applicable CS procedure continues, e.g. for Supplementary Service as specified in specifications such as TS 23.090 [10].
When SRVCC capable UE is in active mode with an IMS VoIP session but the network does not support SRVCC, MME sends Paging Reject towards MSC and this CSFB procedure stops. This is based on the bearer information at MME indicating UE has IMS VoIP session, i.e. EPS bearer with QCI=1.
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8.4.3 Returning back to E-UTRAN
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Once CS service ends in CS domain, existing mechanisms as specified in TS 23.401 [2] can be used to move the UE to E‑UTRAN, no specific CS Fallback mechanisms are needed. During the release of an RR connection the MSC should indicate to GERAN/UTRAN that the RR connection (for call or CISS or LCS) was established as a result of CS fallback. GERAN and UTRAN may use the indication to determine which of the existing mechanisms that should be used to move the UE to E‑UTRAN. When configured to support the return to the last used PLMN after CSFB, after a successful setup of an RR connection or during the release of the UTRAN RR connection, the MSC shall further indicate to GERAN/UTRAN the last used LTE PLMN ID. GERAN and UTRAN shall take the last used LTE PLMN ID into account when selecting the target cell in PS handover to E-UTRAN or when selecting the dedicated target frequency list for idle mode mobility to E-UTRAN in RR Connection Release procedure. Annex A (informative): Void Annex B (normative): CS Fallback to 1xRTT This annex describes a CS Fallback to 1xRTT and an SMS solution for dual mode 1xRTT/E-UTRAN terminals. CS Fallback to 1xRTT is supported for UEs with both single Rx and dual Rx configuration (see TS 36.331 [33]). UEs with single Rx configuration are not able to camp in 1xRTT when they are active in E-UTRAN. The network therefore provides mechanisms for the UE to perform registration to 1xRTT, receive 1xRTT paging, SMS etc. while the UE is in E-UTRAN. UEs with dual Rx configuration can camp in 1xRTT while they are active in E-UTRAN, they may however not be able to stay in E-UTRAN when they handle a CS call and/or perform registration signalling, and/or sending or receiving SMS in 1xRTT. Clause B.1 and B.2 describes the architecture and procedures for CS Fallback (and enhanced CS Fallback) to 1xRTT when the UE has single Rx, dual Rx, or dual Rx/Tx configuration. In this scenario the network need to support the S102 interface between the MME and 1xCS system in order to support CS Fallback (this is indicated by the presence of CSFB registration parameters on E-UTRAN broadcast channel, TS 36.331 [33]). Clause B.3 describes the procedures for CS Fallback when the UE has dual Rx configuration. In this scenario the network needs to support the Extended Service Request procedure in order to support CS Fallback (this is indicated by either the presence of CSFB registration parameters or indication of support for dual rx CSFB on E-UTRAN broadcast channel, TS 36.331 [33]). If the UE has a dual Rx configuration and indicates support for enhanced CS fallback to 1xRTT in the UE radio capabilities, the principles and procedures in clauses B.1 and B.2 are followed when the network indicates support for S102. B.1 Overall Description B.1.1 General Considerations The CS fallback for 1xRTT in EPS enables the delivery of CS-domain services (e.g. CS voice) by reuse of the 1xCS infrastructure when the UE is served by E-UTRAN. A CS fallback enabled terminal, while connected to E-UTRAN may register in the 1x RTT CS domain in order to be able to use 1xRTT access to establish one or more CS services in the CS domain. The CS Fallback function is only available where E-UTRAN coverage overlaps with 1xRTT coverage. This specification also specifies the architecture required for SMS over S102 in EPS. The MO SMS and MT SMS are tunnelled in EPS and over S102 and do not cause any CS Fallback to CDMA 1xRTT, and consequently does not require any overlapped CDMA 1xRTT coverage. CS Fallback to 1xRTT and IMS-based services shall be able to co-exist in the same operator's network. CS Fallback to 1xRTT with PS Handover procedure to HRPD access for Optimised HO, non-Optimised HO, and Optimised Idle mode mobility as defined in TS 23.402 [27] shall be able to co-exist in the same operator's network. B.1.2 Reference Architecture The CS fallback to 1xRTT and SMS over S102 in EPS function is realised by reusing the S102 reference point between the MME and the 1xCS IWS. The reference architecture described in figure B.1.2‑1 is similar to the SRVCC architecture for E‑UTRAN to 3GPP2 1xCS described in TS 23.216 [20], with the additional aspect that the S102 session is long‑lived (similar to pre‑registration for S101). Figure B.1.2-1: Reference architecture for CS fallback to 1xRTT CS Reference architecture for PS handover procedure between E-UTRAN and HRPD access is defined in TS 23.402 [27]. B.1.2.1 Reference points S102: It is the reference point between the MME and the 1xCS IWS. The S102 reference point provides a tunnel between MME and 3GPP2 1xCS IWS to relay 3GPP2 1xCS signalling messages. 1x CS signalling messages are those messages that are defined for A21 interface as described in 3GPP2 A.S0008-C [16] and 3GPP2 A.S0009 [17]. B.1.3 Functional entities B.1.3.1 UE The UE capable of CS fallback to 1xRTT and SMS over S102 supports access to E-UTRAN/EPC as well as access to the 1xCS domain over 1xRTT. It supports the following additional functions: - 1xRTT CS registration over the EPS after the UE has completed the E-UTRAN attachment; - 1xRTT CS re-registration due to mobility; - CS fallback procedures specified for 1xRTT CS domain voice service; - Procedures for mobile originated and mobile terminated SMS tunnelled over EPS and S102; - Includes enhanced CS fallback to 1xRTT capability indication as part of the UE radio capabilities; - Includes concurrent 1xRTT and HRPD capability indication as part of the UE radio capabilities if supported by the enhanced CS fallback to 1xRTT capable UE. If the UE is service user with subscription to CS domain priority service, the UE's USIM belongs to one of the special Access Classes as specified in TS 22.011 [38] and the UE shall set the RRC establishment cause to "HighPriorityAccess" as specified in TS 36.331 [33]. B.1.3.2 MME The MME enabled for CS fallback to 1xRTT supports the following additional functions: - It serves as a signalling tunnelling end point towards the 3GPP2 1xCS IWS via S102 interface for sending/receiving encapsulated 3GPP2 1xCS signalling messages to/from the UE, which are encapsulated in S1-MME S1 Information Transfer messages, as defined in TR 36.938 [19]; - 1xCS-IWS (terminating S102 reference point) selection for CSFB procedures; - Handling of S102 tunnel redirection in case of MME relocation; - Buffering of messages received via S102 for UEs in idle state. If the network supports CSFB priority call handling, the MME supports the following additional functions: - For page message received on the S102 interface with priority indication, the MME provides preferential treatment to this message and also the subsequent CS fallback procedure compared to other normal transactions. If UE needs to be paged, the MME sets priority indication on the paging request to eNodeB. The MME also sets priority indication, i.e. "CSFB High Priority", in S1AP message to the eNodeB, so that eNodeB may initiate the CSFB procedure with priority, as specified in TS 36.413 [35]. - For a CSFB request from service user, the MME determines that the CSFB request need priority handling based on the UE's EPS subscription information. The MME in congestion situation provides preferential treatment to this request and also sets priority indication, i.e. "CSFB High Priority", in S1AP message to eNodeB to initiate CSFB procedure, as specified in TS 36.413 [35]. B.1.3.3 E-UTRAN The E‑UTRAN enabled for CS fallback to 1xRTT supports the following additional functions: - Provision of control information that causes the UE to trigger 1xCS registration; - Forwarding 1x RTT CS paging request to the UE; - Forwarding 1x RTT CS related messages between MME and UE; - Release of E-UTRAN resources after UE leaves E-UTRAN coverage subsequent to a page for CS fallback to 1xRTT CS if PS handover procedure is not performed in conjunction with 1xCS fallback; - Invoking the optimised or non-optimised PS handover procedure concurrently with enhanced 1xCS fallback procedure when supported by the network and UE, and based on network configuration. If the network supports CSFB priority call handling, the E-UTRAN supports the following additional functions: - For page message received on S1AP with priority indication, the E-UTRAN should provide preferential treatment to this request compared to other normal paging requests. - For CS fallback S1AP message with priority indication and if the UE is idle, the E-UTRAN should provide preferential treatment in allocating E-UTRAN radio bearer resources compared to other normal resource requests. Also, E-UTRAN shall not trigger enhanced 1xCSFB with concurrent optimized PS handover to HRPD access. B.1.4 Co-existence with IMS services Clause 4.5 of this specification also applies here. B.1.5 CSFB Priority Call Handling Priority call handling support for CSFB ensures that end-to-end priority handling is provided for both mobile originated CSFB calls by a service user in E-UTRAN and for mobile terminated CSFB call from a service user to a normal or service user in E-UTRAN. A service user's EPS subscription information contains an indication of the users 1xRTT CS domain priority status, i.e. a MPS CS priority. If the UE is subscribed to CS domain priority, the UE's USIM shall belong to one of special Access Classes as specified in TS 22.011 [38]. For mobile terminated CS fallback calls from a service user, the 1x MSC via the 1xCS IWS provides a priority indication to the MME along with a page message. The MME shall set a priority indication to the eNodeB when requesting the eNodeB to page the UE if the UE is idle. If the MME, while waiting for a UE response to the paging request sent without priority indication, receives a message with priority indication from the 1xCS MSC via 1xCS IWS, the MME should send another paging request with priority indication. For mobile originated CS fallback calls from a service user in E-UTRAN, the MME determines that the CSFB requires priority handling based on the MPS CS priority in the UE's EPS subscription. For both mobile originated and mobile terminated CSFB, the MME shall also provide priority indication, i.e. "CSFB High Priority", when requesting the eNodeB to execute the CSFB priority procedure. The eNodeB should handle the page message with priority and also prioritize the subsequent CS fallback procedure to 1xRTT as specified in TS 36.413 [35]. B.2 Procedures B.2.1 Mobility Management B.2.1.1 1x RTT CS Pre-Registration over EPS Procedure This clause describes how the UE in an E-UTRAN system establishes and maintains pre-registration in the 1xCS system. Figure B.2.1.1-1: 1xRTT CS registration procedure 1. The UE attaches to E-UTRAN as specified in TS 23.401 [2]. The UE includes an indication of enhanced CS fallback to 1xRTT and may also include concurrent 1xRTT and HRPD PS session handling capabilities as part of the UE radio capabilities. If the UE is a service user with subscription to 1x priority service in the 1xRTT CS domain, the UE's EPS subscription contains MPS CS priority. 2. Based on a radio layer trigger (e.g. an indication from the E-UTRAN when the UE is in connected state or an indication over the broadcast channel), the UE decides to register with the 1xRTT CS domain. 3. If the UE is in idle state, in order to create a signalling connection with the MME, it performs the Service Request procedure. 4. The UE generates a 1xRTT CS registration request. 4a. The 1xRTT CS message is transferred from the UE to E-UTRAN. 4b. E-UTRAN forwards the 1xRTT CS message to the MME including the CDMA2000 Reference Cell ID. 4c. The MME selects a 1xCS IWS node based on the CDMA2000 Reference Cell ID. The IMSI is used to distinguish S102 signalling transactions belonging to different UEs. The MME sends a S102 Direct Transfer message (IMSI, 1xCS message) to the 1xCS IWS node. 5. 1xRTT CS registration is then performed by the 1xCS IWS node based on 3GPP2 A.S0008 [16]. 6a. 1xRTT CS registration response is tunnelled back to the MME in a S102 Direct Transfer message (IMSI, 1xCS message). 6b. The MME forwards the 1xRTT CS message to the E-UTRAN. 6c. The E-UTRAN forwards the 1xRTT CS message to the UE. If the triggers for 1xCS registration change over time, the UE (both in idle or connected state), uses this information to update the 1xCS registration via the tunnel. B.2.1.2 S102 Tunnel Redirection S102 Tunnel Redirection Procedure is used when the UE perform Tracking Area Update with MME change while the UE is registered with the 1xRTT CS domain as described in clause B.2.1.1 and the S102 session exists between the MME and the 1xCS IWS. The detail procedure for the idle case is depicted as figure B.2.1.2-1. Figure B.2.1.2-1: S102 tunnel redirection during TAU with MME change 1. UE performs 1x-registration over the source MME while in ECM-CONNECTED state, followed by transition to ECM-IDLE state. The S102 tunnel exists between the source MME and the 1xCS IWS. 2. TAU procedure with MME change as described in TS 23.401 [2], figure 5.3.3.1-1, up to and including the step where the target MME receives Update Location Ack from the HSS, is executed. The 1xCS IWS ID is transferred to the target MME via the Context Response message. 3. The target MME sends S102 Redirection Command message to the 1xCS IWS. After receiving this message, the 1xCS IWS associates the S102 tunnel for this specific UE with the target MME. Then the 1xCS IWS releases any context associated with the source MME. 4. In response to the S102 Redirection Command message, the 1xCS IWS sends a S102 Redirection Ack message to the target MME. 5. The TAU procedure is completed. The detailed procedure for the active case is depicted as figure B.2.1.2-2. Figure B.2.1.2-2: S102 tunnel redirection during inter-eNodeB handover with MME relocation 1. UE performs 1x-registration over the source MME while in ECM-CONNECTED state. The S102 tunnel exists between the source MME and the 1xCS IWS. 2. Inter-eNodeB handover with MME relocation procedure as described in TS 23.401 [2], figure 5.5.1.2.2-1, steps prior to TAU, is executed. The 1xCS IWS ID is transferred to the target MME via the Forward Relocation Request message. 3. The target MME sends S102 Redirection Command message to the 1xCS IWS. After receiving this message, the 1xCS IWS associates the S102 tunnel with the target MME. Then the 1xCS IWS releases any context associated with the source MME. 4. In response to the S102 Redirection Command message, the 1xCS IWS sends a S102 Redirection Ack message to the target MME. 5. The TAU procedure occurs. B.2.1.3 UE-initiated Detach Procedure If a 1xRTT CS Fallback UE, pre-registered to the 1xRTT CS system, initiates the detach procedure in E-UTRAN access due to switch off and the UE is required to perform a "power-down registration" in the 1xRTT CS system (see C.S0005‑A [32]), the UE shall first perform the "power-down registration" procedure with the 1xRTT CS system via the S102 tunnel, before initiating the detach procedure in E-UTRAN access as specified in TS 23.401 [2]. A 1xCSF UE, pre-registered to the 1xCS system, performing detach due to reasons other than switch off is not required to perform "power-down registration" with the 1xCS system prior to performing the detach procedure in E-UTRAN. B.2.2 Mobile Originating Call in Active Mode This clause describes the mobile originating call procedures for the CS Fallback to 1xRTT in the normal case. For enhanced CS fallback to 1xRTT procedure, see clause B.2.3a. Clause B.2.3b describes the procedure when the procedure is rejected by the MME. Figure B.2.2-1: CS MO call using fallback to CDMA 1x RTT network 1. UE is E‑UTRAN attached and registered with 1xRTT CS as defined in clause B.2.1.1. 2. UE makes a decision to perform a mobile originated CS call. 3. UE sends an Extended Service Request for mobile originating 1xCS fallback to the MME. 4. MME sends UE Context Modification Request (CS Fallback Indicator, priority indicator) to E-UTRAN. CS Fallback Indicator indicates to the E‑UTRAN to move the UE to 1xRTT. If MME determines the CS Fallback procedure needs priority handling based on the MPS CS priority in the UE's EPS subscription, it sets priority indication in the S1AP message to the E-UTRAN. E-UTRAN responds with UE Context Modification Response 5. E-UTRAN may optionally solicit a 1xRTT measurement report from the UE to determine the target 1xRTT cell to which the CS Fallback will be performed. 6a. The E-UTRAN triggers RRC connection release with redirection to 1xCS and continue with step 7. 7. E-UTRAN sends an S1 UE Context Release Request (Cause) message to the MME. Cause indicates that the S1 UE Context Release was caused by CS fallback to 1xRTT. In case the Cause indicates that RRC was released due to abnormal conditions, e.g. radio link failure, the MME should continue with steps 8 -10. 8. The MME deactivates GBR bearers towards S-GW and P-GW(s) by initiating MME-initiated Dedicated Bearer Deactivation procedure as specified in TS 23.401 [2], and starts the preservation and suspension of non-GBR bearers by sending Suspend Notification message to the S-GW. The S-GW releases all eNodeB related information (address and TEIDs) for the UE, and sends Suspend Notification message to the P-GW(s). 9. S-GW and P-GW(s) acknowledges the bearer updates by responding with Suspend Acknowledge. The MME stores in the UE context that UE is in suspended status. All the preserved non-GBR bearers are marked as suspended status in S-GW and P-GW. The P-GW discards downlink data if the UE is marked as suspended. 10. S1 UE Context in the E-UTRAN is released as specified in TS 23.401 [2]. 11. UE moves to 1xRTT and performs the procedure for mobile originating call as specified in 3GPP2 A.S0013 [18]. Once CS service ends in the 1xCS domain, the UE returns to E‑UTRAN by performing reselection. The EPS service is resumed as described in clause 6.5. B.2.2a Mobile Originating call in Idle Mode Mobile Originating call in Idle Mode procedure is specified by reusing the Mobile Originating Call in Active mode procedure with Extended Service Request for mobile originating 1xCS fallback to the MME where the messages S1-AP UE context Modification Request and Response are replaced by S1-AP Initial UE Context Request and Response. UE is transited to ECM-CONNECTED mode by following the applicable procedures specified in TS 23.401 [2]. If UE has only LIPA PDN connection and the cell accessed by the UE does not link to the L-GW where the UE had the LIPA PDN Connection, the MME shall reject the Extended Service Request with a reason code which results in the UE selecting 1xRTT access as specified in TS 24.301 [34]. If the UE has only SIPTO at the Local Network PDN connections: (i) in a network with collocated L-GW deployment and the (H)eNB accessed by the UE is not collocated with the L-GW providing the SIPTO at the Local Network connectivity; or (ii) in a network with stand-alone GW deployment and the (H)eNB accessed by the UE is not connected to the Local Network where the stand-alone GW (with S-GW and L-GW collocated) providing the SIPTO at the Local Network connectivity is residing, the MME shall reject the Extended Service Request with an appropriate cause value which results in the UE selecting 1xRTT access. If the UE has only SIPTO at the Local Network PDN connections and LIPA PDN connections, where: - the SIPTO at the Local Network PDN connections fulfil criterion (i) or (ii) above; and - the cell accessed by the UE does not link to the L-GW where the UE had the LIPA PDN connection, the MME shall also reject the Extended Service Request with an appropriate cause value which results in the UE selecting 1xRTT access. If the UE is a service user with subscription to CS domain priority service, the UE's USIM shall belong to one of special Access Classes as specified in TS 22.011 [38] and sets the RRC establishment cause to "HighPriorityAccess" as specified in TS 36.331 [33]. If the network supports a priority call handling, the MME determines that the Extended Service Request requires priority handling of CS Fallback based on the "HighPriorityAccess" establishment cause forwarded by eNodeB to the MME and/or MPS CS priority in the UE's EPS subscription. According to operator policy, the MME may use MPS CS priority to verify the priority handling of the CS Fallback procedure. If MME decides to perform CS Fallback with priority, it sets priority indication in the S1-AP Initial UE Context Request message to the eNodeB. The eNodeB should allocate radio bearer resources to the UE preferentially compared to other normal calls. B.2.3 Mobile Terminating Call This clause describes the mobile terminating call procedures when the UE accepts or rejects CS paging for the CS Fallback to 1xRTT, in the normal case. Clause B.2.3b describes the procedure when the procedure is rejected by the MME. When the 1x MSC receives a registration from a UE, it makes note of the RAN equipment from which it received the registration. Subsequent paging activities may thus be directed toward that RAN equipment. However, paging activities by the 1xMSC are not limited to the single RAN equipment from which the registration was received. The MSC may choose to page a wider area, including inter‑system paging. If the 1xMSC has direct interfaces to 1xCS IWS, as well as to 1xRTT access, the MSC may choose to do direct paging activities to both E‑UTRAN and 1x RAN equipments in its attempts to contact the UE. The 1x paging request sent by the 1xMSC to the 1xCS IWS is delivered to the UE via the tunnel. The UE tunes to 1xRTT access, acknowledges the 1x page and performs the 1xCS procedures for mobile terminated call. The detailed procedure using RRC connection release with redirection to 1xCS is described in figure B.2.3‑1. For enhanced 1xRTT CS Fall Back procedure, see clause B.2.3a. Figure B.2.3-1: CS MT call using fallback to CDMA 1x RTT network 1. UE is E-UTRAN attached and pre-registered with 1xRTT CS as defined in clause B.2.1.1. 2. 1xMSC sends a paging request to the 1xCS IWS node with Caller Line Identification if available. If the call is originated by a priority user or an emergency callback from PSAP, the paging request message from the 1xRTT MSC to the IWS contains a priority value or an emergency indicator, respectively, as specified in 3GPP2 specification A.S0008-C v3.0 [39] / A.S0009-C v3.0 [40]. 3. 1xCS IWS node forwards the 1x RTT CS paging request via the S102 tunnel to the MME. If a priority value or emergency indication was received in the previous step, the S102 message also reflects the same. 4. If the UE is in idle state, the MME performs the network initiated Service Request procedure in order to bring the UE to active state prior to tunnelling of the 1x RTT CS paging request toward the UE. The paging is performed using S-TMSI with CN domain indicator set to "PS". If the S102 message contains a priority value or emergency indication, the MME also sets priority indication in the S1AP paging request message to the E-UTRAN. The E-UTRAN handles the paging process with priority. 5. MME forwards the 1xRTT CS paging request to the UE. 6a. Void. 6b. If the UE accepts CS paging for the CS Fallback to 1xRTT, the UE sends an Extended Service Request for mobile terminating 1xCS fallback to the MME and proceeds with step 7 to step 15 below. 7. MME sends UE Context Modification Request (CS Fallback Indicator) to indicate the E‑UTRAN to move the UE to 1xRTT. If priority value or emergency indication was received in Step 3, the MME also sets priority indication to the E-UTRAN in UE Context Modification Request. The E-UTRAN provides preferential treatment to this call in the subsequent steps. E-UTRAN responds with UE Context Modification Response. 8. E-UTRAN may optionally solicit a 1xRTT measurement report from the UE to determine the target 1xRTT cell to which the CS Fallback will be performed. 9. E-UTRAN triggers RRC connection release with redirection to 1xCS. 10. E-UTRAN sends an S1 UE Context Release Request (Cause) message to the MME. Cause indicates that the S1 UE Context Release was caused by CS fallback to 1xRTT. 11. The MME deactivates GBR bearers towards S-GW and P-GW(s) by initiating MME-initiated Dedicated Bearer Deactivation procedure as specified in TS 23.401 [2], and starts the preservation and suspension of non-GBR bearers by sending Suspend Notification message to the S-GW. The S-GW releases all eNodeB related information (address and TEIDs) for the UE, and sends Suspend Notification message to the P-GW(s). 12. S-GW and P-GW(s) acknowledges the bearer updates by responding with Suspend Acknowledge. The MME stores in the UE context that UE is in suspended status. All the preserved non-GBR bearers are marked as suspended status in S-GW and P-GW. The P-GW discards downlink data if the UE is marked as suspended. 13. S1 UE Context in the E-UTRAN is released as specified in TS 23.401 [2]. 14. UE tunes to 1xRTT and acknowledges the page by transmitting a 1xRTT Paging Response message over the 1x Access Channel. 15. Subsequently UE performs the procedure for mobile terminated call establishment as specified in 3GPP2 A.S0013 [18]. Once CS service ends in the 1xCS domain the UE returns to E-UTRAN by performing reselection. The EPS service is resumed as described in clause 6.5. B.2.3a Enhanced CS fallback to 1xRTT Procedure B.2.3a.1 General Enhanced CS fallback to 1xRTT procedure may be used when the UE indicates its support of this capability to the network. If in addition, the UE also indicates its support of concurrent 1xRTT and HRPD PS session handling, this indication also allows the network to invoke optimised or non-optimised PS handover procedure concurrently with the enhanced CS fallback to 1xRTT procedure. A network that advertises support for enhanced CS fallback to 1xRTT may also advertise support for UEs with dual 1xRTT and E-UTRAN receiver/transmitter configuration. In such networks, UEs that support enhanced CS fallback to 1xRTT for dual receiver/transmitter configuration may switch off their 1xRTT receiver/transmitter while camped in E-UTRAN and register in the 1xRTT domain via the S102 tunnel. A network advertising these capabilities does not suspend the EPS bearers for mobile originated or mobile terminated 1x CS calls for such UEs. Concurrent enhanced CS fallback to 1xRTT and PS handover to HRPD is not performed for UEs that support enhanced CS fallback to 1xRTT for dual receiver/transmitter configuration. If enhanced CS fallback to 1xRTT procedure is not used by the network (i.e., not supported or not configured), the network uses RRC connection release with redirection as specified in clauses B.2.2 and B.2.3. NOTE 1. Other 3GPP2 specific procedure (e.g. how UE performs concurrent operation in 3GPP2 network) is outside the scope of this specification. NOTE 2. E-UTRAN may invoke concurrent optimised active-mode PS handover procedure or non-optimised PS handover procedure when it receives S1-AP: UE Context Modification with CSFB indication, based on UE capability and operator configuration. B.2.3a.2 Mobile Originating Call without concurrent PS handover, or with concurrent non-optimised PS handover or optimised idle-mode PS handover The following figure describes the mobile originating call procedures for the enhanced CS Fallback to 1xRTT with concurrent non-optimised PS handover or optimised idle-mode PS handover, or without concurrent PS handover, in the normal case. Clause B.2.3b describes the procedure when the procedure is rejected by the MME. Figure B.2.3a.2-1: Enhanced CS fallback to 1xRTT MO Call with no PS handover, or with concurrent non-optimised PS handover or optimised idle-mode PS handover 1. UE is E UTRAN attached and registered with 1xRTT CS as defined in clause B.2.1.1 with enhanced CS fallback to 1xRTT capability indication to E-UTRAN. The UE may also indicate that it supports concurrent 1xRTT and HRPD capability. The UE may also be pre-registered with HRPD access using procedures defined in TS 23.402 [27], clause 9.3.1. The UE may also indicate support of enhanced CS Fallback to 1xRTT for dual receiver/transmitter configuration to E-UTRAN. 2. UE makes a decision to perform a mobile originated CS call. 3. UE sends an Extended Service Request for mobile originating 1xCS fallback to the MME. 4. For a UE in active mode, MME sends UE Context Modification Request (CS Fallback Indicator) to E-UTRAN. CS Fallback Indicator indicates to the E UTRAN to move the UE to 1xRTT. E-UTRAN responds with UE Context Modification Response. For a UE in idle mode, MME sends Initial UE Context Request (CS Fallback Indicator) to E-UTRAN. CS Fallback Indicator indicates to the E‑UTRAN to move the UE to 1xRTT. E-UTRAN responds with Initial UE Context Response. If MME determines the CS Fallback procedure needs priority handling based on MPS CS priority in the UE's EPS subscription and/or the high priority access indication that the eNodeB includes in the S1AP message in step 3, it sets priority indication as well as CS Fallback indicator in the S1AP message to the eNodeB. According to operator policy the MME may use CS priority indicator to verify the priority handling of the CS Fallback procedure, in the case high priority access indication is received in the S1-AP message. The E-UTRAN, in congestion conditions, provides preferential treatment for this call in the subsequent steps. Also, the E-UTRAN shall not trigger enhanced 1xCSFB with concurrent optimized PS handover to HRPD access. 5. E-UTRAN may optionally solicit a 1xRTT measurement report from the UE to determine the target 1xRTT cell to which the CS Fallback will be performed. If the network supports PS handover procedure to HRPD then E-UTRAN may optionally solicit an HRPD measurement report from the UE to determine whether the target HRPD candidates exist or not. 6. E-UTRAN sends a HandoverFromE-UTRAPreparation Request message to the UE to start the enhanced 1xCS fallback procedure. It includes 3G1x Overhead Parameters and RAND value. This message also includes an indication that concurrent HRPD handover preparation is not required. When both the network and the UE support enhanced CS Fallback to 1xRTT for dual receiver/transmitter configuration, the E-UTRAN may after Step 4 decide, e.g. due to RF conditions, to direct the UE to turn on its second radio to 1xRTT and retry the 1xCS call directly on the 1xRTT access network. For this case, the E-UTRAN in the HandoverFromE-UTRAPreparation Request message includes a redirection indicator along with optional redirection information. The procedure stops after this step and the UE tunes its 1x radio and retries its 1x call in 1xRTT while still receiving/transmitting data on E‑UTRAN. 7. The UE initiates signalling for establishment of the CS access leg by sending UL HandoverPreparation Transfer message which contains the 1xRTT Origination message with called party number. 8. Messages between MME and 1xIWS are tunnelled using the S102 interface. The 1xRTT MSC initiates the call with the called party number carried in the 1xRTT Origination message. 9. The E-UTRAN performs either Step 9a or Step 9b. Step 9b is only performed when both the E-UTRAN and UE support enhanced 1x CS fallback to 1xRTT for dual receiver/transmitter configuration. 9a. The E UTRAN sends Mobility from EUTRA Command to the UE with indication that this is for enhanced 1x CS Fallback operation, 1xRTT related information, and optionally the HRPD redirection information. The 1xRTT information contains 1xRTT messages related to 1x channel assignment and cause the UE to tune to and acquire this 1x channel. This is perceived by the UE as a Handover Command message to 1xRTT. - If the network does not support PS handover procedure to HRPD or if no target HRPD candidates exist then E-UTRAN shall release the S1 UE context (see step 10a/b) after executing the enhanced CS fallback to 1xRTT procedure. - For either concurrent non-optimised PS handover procedure or optimised idle-mode PS handover procedure along with enhanced CS fallback to 1xRTT, E-UTRAN may also redirect the UE to HRPD as part of this procedure. This is indicated by the HRPD redirection information in the Mobility from EUTRA Command. If 1xRTT CS network cannot support this CSFB request (for example due to resource availability), the DL information transfer message is sent instead, with an embedded 1x message that indicates failure to the UE. In this case, steps 10, 11, 12 shall be skipped. 9b. The E‑UTRAN sends DL information transfer message, with the embedded 1x message indicating 1xRTT preparation success to the UE. Steps 10 and 12 are not performed in this case. 10a/b/c. If PS handover procedure is not performed then E-UTRAN sends an S1 UE Context Release Request (Cause) message to the MME. Cause indicates that the S1 UE Context Release was caused by CS fallback to 1xRTT. The S1-U bearers are released and the MME starts the preservation and suspension of non-GBR bearers and the deactivation of GBR bearers towards S-GW and P-GW(s). The MME sets the UE context to suspended status. 11. UE tunes to the 1xRTT radio access network and performs 1xchannel acquisition with the 1xRTT CS access (e.g. 1xRTT BSS). A UE supporting enhanced 1xCSFB to 1xRTT for dual receiver/transmitter configuration continues to receive/transmit data on E-UTRAN. 12.UE and Network follow the appropriate procedure for handling non-optimised PS handover procedure or optimised idle-mode PS handover as defined in TS 23.402 [27] if performed. S1 UE Context release procedure is as specified in TS 23.402 [27] for non-optimised PS handover (clause 8.2.2) or optimised idle-mode PS handover (clause 9.4). This step occurs in parallel with step 11. B.2.3a.3 Mobile Originating Call with concurrent optimised PS handover The following figure describes the mobile originating call procedures for the enhanced CS Fallback procedure to 1xRTT with concurrent optimised PS handover, in the normal case. Clause B.2.3b describes the procedure when the procedure is rejected by the MME. This procedure is not executed for mobile originated priority 1x CS Fallback. This procedure is not performed when both the network and the UE support enhanced CS Fallback to 1xRTT for dual receiver/transmitter configuration. Figure B.2.3a.3-1: Enhanced CS fallback to 1xRTT MO Call with concurrent optimised PS handover 1-5. Same as steps 1-5 in figure B.2.3a.2-1. The UE indicates that it supports enhanced CS fallback to 1xRTT procedure and concurrent 1xRTT and HRPD capability. 6. E-UTRAN sends an Handover From E-UTRA Preparation Request message to the UE to start the enhanced 1xCS fallback procedure. It includes 3G1x Overhead Parameters and RAND value. This message also includes an indication that concurrent HRPD handover preparation is required. 7. UE starts the enhanced 1xCS fallback and optimised PS handover messages (7a, 7b) in a sequential manner. Step 7a contains the 1xRTT Origination message with called party number. 8a, 9a, 10a, and 8b, 9b, 10b. MME treats the enhanced 1xCS fallback and HRPD PS handover procedure independently (i.e. MME does not link the HRPD message and 1xCS fallback message together). 8a, 9a, 10a is same as shown in step 8 in figure B.2.3a.2-1 8b, 9b, 10b are messages/procedure for optimised E‑UTRAN to HRPD handover procedure as defined in TS 23.402 [27], clause 9.3.2. 11. The E-UTRAN sends Mobility from EUTRA Command to the UE with indication that this is for enhanced 1x CS Fallback operation including the 1xRTT message and the HRPD message received over the S102 and S101 tunnels. If handover preparation to HRPD is successful but preparation failure message in received from the 1xRTT CS network via the S102 tunnel, the message for 1xRTT preparation failure indication is sent to the UE as part of the Mobility from EUTRA Command. If handover to HRPD is successful and the eNodeB times out waiting for preparation completion message from 1xRTT, the E-UTRAN sends a Mobility from EUTRA command with only the HPRD message included. In the case that the preparation to HRPD failed but 1xRTT is successful, E‑UTRAN may optionally include HRPD redirection info as part of the Mobility from EUTRA Command. In case preparation on 1xRTT and HRPD failed with explicit failure messages received on S102 and S01 tunnels, the E-UTRAN forwards the received failure messages as DL Information transfers. In this case, steps 12 and 13 are skipped. 12. UE retunes to the 1xRTT radio access network and performs 1x channel acquisition with the 1xRTT CS access (e.g. 1xRTT BSS), see TS 23.216 [20], clause 6.1.3. 13. UE and network follow the optimised E-UTRAN to HRPD handover procedure. UE context release procedure follows the optimised E-UTRAN to HRPD handover procedure as defined in TS 23.402 [27], clause 9.3.2. This step occurs in parallel with step 12. B.2.3a.4 Mobile Terminating Call without PS handover, or with concurrent non-optimised PS handover or optimised idle-mode PS handover The following figure describes the mobile terminating call procedures for the enhanced CS Fallback to 1xRTT with concurrent non-optimised PS handover or optimised idle-mode PS handover, or without PS handover, in the normal case. Clause B.2.3b describes the procedure when the procedure is rejected by the MME. Figure B.2.3a.4-1: Enhanced CS fallback to 1xRTT MT call without PS handover, or with concurrent non-optimised PS handover or optimised idle-mode PS handover 1. UE is E‑UTRAN attached and pre-registered with 1xRTT CS as defined in clause B.2.1.1 with enhanced CS fallback to 1xRTT capability indication to E-UTRAN. The UE may also indicate that it supports concurrent 1xRTT and HRPD capability The UE may also be pre-register with HRPD access using procedures defined in TS 23.402 [27], clause 9.3.1. The UE may also indicate support of enhanced CS fallback to 1xRTT for dual receiver/transmitter configuration to E-UTRAN. 2-7. Same as step 2-7 in figure B.2.3-1. If priority indication in included in the S1AP UE Context Setup or modification message from the MME to the E-UTRAN, the E-UTRAN shall not initiate enhanced 1xCSFB with concurrent optimized PS handover to HRPD access. 8-17. Same as steps 5 – 12 of Figure B.2.3a.2-1, with the modifications that the 1x message in step 7 of Figure B.2.3a.2-1 provided by the UE to the E-UTRAN is a 1xPage Response message and 1x messages in step 9a of Figure B.2.3.a.2-1 (step 14a of Figure B.2.3a.4-1) provided by the E-UTRAN to UE may also contain Alert With Information message to provide caller line Identification and alerting trigger with 1x channel assignment message. B.2.3a.5 Mobile Terminating Call with concurrent optimised PS handover The following figure describes the mobile terminating call procedures for the enhanced CS Fallback to 1xRTT with concurrent optimised PS handover, in the normal case. Clause B.2.3b describes the procedure when the procedure is rejected by the MME. This procedure is not executed for mobile terminated priority 1x CS Fallback. This procedure is not performed when both the network and the UE support enhanced CS Fallback to 1xRTT for dual receiver/transmitter configuration. Figure B.2.3a.5-1: Enhanced CS fallback to 1xRTT MT Call with concurrent optimised PS handover 1-8. Same as steps 1-8 in figure B.2.3a.4-1. The UE indicates that it supports enhanced CS fallback to 1xRTT procedures and concurrent 1xRTT and HRPD capability. The UE may also be pre-register with HRPD access using procedures defined in TS 23.402 [27], clause 9.3.1. 9-16. Same as steps 6 – 13 of Figure B.2.3a.3-1, with the modifications that the 1x message in step 7 of Figure B.2.3a.2-1 provided by the UE to the E-UTRAN is a 1xPage Response message and 1x messages in step 9a of Figure B.2.3.a.2-1 (step 14 of Figure B.2.3a.5-1) provided by the E-UTRAN to UE may also contain Alert With Information message to provide caller line Identification and alerting trigger with 1x channel assignment message. B.2.3a.6 Interaction between enhanced CS Fallback to 1xRTT and optimised PS handover For regular optimized PS handover procedure, it is possible that the UE receives 1xRTT CS paging from EPS while optimised PS handover to HRPD is in progress. In this case, UE shall ignore the 1xRTT CS paging locally. B.2.3b Mobile Originated or Mobile terminated call rejected by the MME The MME may reject an Extended Service Request either for mobile originated or mobile terminated CSFB. In this case, the following procedure is executed. Figure B.2.3b-1: 1xCSFB MO or MT call, rejected by MME 1. UE is E-UTRAN attached and pre-registered with 1xRTT CS as defined in clause B.2.1.1. 2. UE makes a decision to perform a mobile originated CS call or accepts CS paging for the CS Fallback to 1xRTT (Step 6a, Clause 5.2.3). 3. UE sends an Extended Service Request for mobile originating/mobile terminating 1xCS fallback to the MME. 4. If the MME decides to reject the Extended Service Request, the MME sends a Service Reject message to the UE. Steps 5 – 10 are executed when Service Reject is sent with a reason code which results in the UE selecting 1xRTT access, as specified in TS 24.301 [34]. 5. The UE selects 1xRTT access without waiting for RRC Release. 6. The MME releases S1 by sending the S1 UE Context Release Command (Cause) message to the eNodeB. Cause value indicates that the release is triggered by CS Fallback procedure. 7. If the RRC connection is not already released, the E-UTRAN sends a RRC Connection Release message to the UE. 8. The E-UTRAN confirms the S1 Release by returning an S1 UE Context Release Complete message to the MME. 9-10. Depending on the reason for rejection, MME may start Suspend Notification: - Suspend Notification: The S1-U bearers are released and the MME starts the preservation and suspension of non-GBR bearers and the deactivation of GBR bearers towards S-GW and P-GW(s). - S-GW and P-GW(s) acknowledges the bearer updates Suspend Notification and marks the UE as suspended. The P-GW discards downlink data if the UE is marked as suspended. B.2.4 Short Message Service (SMS) B.2.4.1 General The procedures for SMS in this annex apply only if the UE is 1xRTT CS Registered and the CS access domain is chosen by the UE and/or the home PLMN for delivering short messages. This clause describes both the mobile originating and mobile terminating SMS over S102 which uses 1xCS procedures in EPS. SMS support is based on the S102 reference point between the MME and the 1xCS IWS, use of RRC Information Transfer message between the UE and the E-UTRAN, and use of S1 cdma2000 Tunnelling message between the E‑UTRAN and the MME. B.2.4.2 Mobile originating SMS The following sequence flow shows the delivery of mobile originating SMS sent via the 1xMSC while in E‑UTRAN. Figure B.2.4.2-1: Mobile originating SMS sent via the 1xMSC while in E-UTRAN 1. The 1xRTT CS Registration procedure as described in clause B.2.1.1 has been performed earlier. 2. A mobile originating short message is triggered. If the UE is in idle state, the UE performs the UE triggered Service Request procedure, which is defined in TS 23.401 [2]. 3. The UE builds the SMS message to be sent as defined in 3GPP2 A.S0008 [16] and 3GPP2 A.S0009 [17]. 3a. The 1xRTT SMS message is transferred from the UE to the E-UTRAN. 3b. The E-UTRAN forwards the SMS message to the MME. 4. The MME forwards the SMS message to the 1xCS IWS in an S102 Direct Transfer message. 5. The 1xCS IWS acknowledges the message. 6. The 1xCS IWS sends an ADDS Transfer message to the 1xMSC containing the SMS message as defined in 3GPP2 A.S0008 [16] and 3GPP2 A.S0009 [17]. 7. The 1xMSC forwards the SMS message to the Message Centre (MC). If an acknowledgement was requested by the UE, the MC responds with an acknowledgement. 8. The 1xMSC forwards the SMS acknowledgement to the 1xCS IWS in an ADDS Page message. 9. The 1xCS IWS forwards the SMS acknowledgement to the MME in an S102 Direct Transfer message. 10. The MME forwards the SMS acknowledgement to the UE. 11. The MME sends an S102 Ack message to the 1xCS IWS. This occurs immediately after step 9 if the MSC has not requested an acknowledgement from the 1xCS IWS. 12. If the MSC requested an acknowledgement, the 1xCS IWS sends an ADDS Page Ack message to the 1xMSC. B.2.4.3 Mobile terminating SMS The following sequence flow shows the delivery of mobile terminating SMS sent via the 1xMSC while in E‑UTRAN. Figure B.2.4.3-1: Mobile terminating SMS sent via the 1xMSC while in E-UTRAN 1. The UE is E-UTRAN attached and registered with 1xRTT CS as defined in clause B.2.1.1. 2. The 1xMSC receives the SMS message from the MC and sends an ADDS Page message to the 1xCS as defined in 3GPP2 A.S0008 [16] and 3GPP2 A.S0009 [17]. The ADDS Page contains the SMS message. 3. The 1xCS IWS sends the SMS message in an S102 Direct Transfer message. 4. If the UE is in idle state, the MME performs the network initiated Service Request procedure to bring the UE to active state prior to tunnelling of the SMS message toward the UE. 5. The MME forwards the SMS message to the UE. 6. The MME sends an S102 Ack message to the 1xCS IWS. This occurs immediately after step 3 if the MSC has not requested an acknowledgement from the 1xCS IWS. 7. If the MSC requested an acknowledgement, the 1xCS IWS sends an ADDS Page Ack message to the 1xMSC. 8. After receiving the SMS message at step 5, the UE sends an SMS acknowledgement toward the MC. 9. The MME forwards the SMS acknowledgement in an S102 Direct Transfer message to the 1xCS IWS. 10. The 1xCS IWS sends an S102 Ack message to the MME. 11. The 1xCS IWS forwards the SMS acknowledgement to the 1xMSC. The 1xMSC then forwards the SMS acknowledgement to the MC. NOTE: In addition to above MT SMS procedure (Common Channel SMS), 3GPP2 also defines Traffic Channel SMS delivering method in 3GPP2 A.S0008[16] and A.S0009 [17] that can be used in E-UTRAN-1x interworking architecture. In this method, the messages between 1xRTT IWS and 1xMSC are different from those messages specified in this clause. There is no additional functional requirement to EPS. B.2.5 Emergency Calls When UE is performing CS fallback procedure to 1xRTT for the purpose of emergency call, it shall indicate to the MME that this CS fallback request is for emergency purpose. MME also indicates to the E-UTRAN via the appropriate S1-AP message that this CS fallback procedure is for emergency purpose. Emergency call with enhanced 1xRTT CS fallback procedure shall be executed without the concurrent PS handover procedure. B.3 CS Fallback for UEs with dual Rx configuration B.3.1 General Considerations The following principles are used for supporting CS Fallback for dual receiver UEs: - The UE with dual Rx configuration attaches separately to each RAT (E-UTRAN, 1xRTT) and maintains separate registration and mobility procedure handling to each RAT. No coordination is required between the E‑UTRAN and 1xRTT network. - The UE with dual Rx configuration is able to camp in 1xRTT at the same time as it is active or idle in E‑UTRAN. Camping in 1xRTT includes performing 1xRTT cell re-selection, reading broadcast channels, monitoring paging, performing location updates, etc. according to 3GPP2 specifications. - The UE with dual Rx configuration is allowed to leave E-UTRAN in order to handle a CS call and/or perform registration signalling, and/or sending or receiving SMS in 1xRTT. The procedures for leaving E-UTRAN is described in clause B.3.2 and are only allowed if the network indicates that it supports them (this is indicated by either the presence of CSFB registration parameters or indication of support for dual Rx CSFB on E‑UTRAN broadcast channel, TS 36.331 [33]). - The UE that reports dual Rx configuration to E‑UTRAN does not require redirection information. NOTE: Further clarification to the UE behaviour may be needed if the procedure in clause B.3.2, i.e. time between transmission of Extended Service Request (3) and reception of RRC Connection Release (5) takes too long. B.3.2 Procedures for leaving E-UTRAN The UE with dual Rx configuration is allowed to leave E-UTRAN in order to handle a CS call and/or perform registration signalling, and/or perform location management signalling, and/or sending or receiving SMS in 1xRTT. When the UE needs to leave E-UTRAN it indicates this to E-UTRAN by using the Extended Service Request procedure similar to how MT/MO calls are handed in clauses B.2.2, B.2.2a and B.2.3. The procedure is the same regardless what activity is performed in the 1xRTT system (e.g. if it is a page response, MO call, re-registration). The procedure is shown in Figure B.3.2-1. Figure B.3.2-1: Performing 1xRTT related activity for dual receiver UEs 1. UE is E‑UTRAN attached the UE may also be registered in 1xRTT CS. 2. UE makes a decision that it needs to perform some 1xRTT activity (e.g. in order to respond to an incoming 1xRTT page, setup a MO call, perform location management signalling, or perform re-registration). 3. UE sends an Extended Service Request for mobile originating/mobile terminating 1xCS fallback to the MME. The figure shows the case the UE is in active state in E-UTRAN but the same principles applies if the UE is in idle state, TS 23.401 [2]. 4. MME sends UE Context modification Request (CS Fallback Indicator) to E-UTRAN. CS Fallback Indicator indicates to the E‑UTRAN to move the UE to 1xRTT. E-UTRAN responds with UE Context Modification Response. 5. The E-UTRAN triggers RRC connection release and continues with step 6. This step may include re-direction information if the E-UTRAN indicates support for S102. E-UTRAN that indicates support for dual Rx CSFB shall not include any redirection information towards the UE that indicates dual Rx configuration but no support for enhanced CS fallback to 1xRTT. 6. E-UTRAN sends an S1 UE Context Release Request (Cause) message to the MME. Cause indicates that the S1 UE Context Release was caused by CS fallback to 1xRTT. 7. The S1-U bearers are released and the MME starts the preservation and suspension of non-GBR bearers and the deactivation of GBR bearers towards S-GW and P-GW(s). by sending Suspend Notification to S-GW and P-GW The MME sets the UE context to suspended status. 8. The S-GW and P-GW(s) acknowledges the bearer updates by responding with Suspend Acknowledge and marks the UE as suspended in S-GW and P-GW. When a downlink data arrives at the P-GW, the P-GW should not send downlink data if the UE is marked as suspended. 9. S1 UE Context in the E-UTRAN is released as specified in TS 23.401 [2]. B.3.3 Procedures for returning to E-UTRAN The procedure for returning to E-UTRAN is the same as specified in clause 6.5. Annex C (normative): SMS in MME C.1 General SMS in MME is an architecture option primarily intended for networks that do not deploy GERAN or UTRAN. SMS in MME delivers SMS services over EPS NAS signalling for UE's requiring SMS services. SMS in MME architecture option enables support of SMS in the EPS via E-UTRAN without requiring deployment of 3GPP MSCs. For SMS in MME the SMS service control is performed by the MME. The MME receives SMS subscriber data and the MME verifies whether the subscriber is permitted to obtain SMS services. The SMS subscriber data received and used by the MME may be PS subscriber data (the MME directly obtains from HSS) or CS subscriber data (the MME obtains via an interworking function as described in clause C.5). NOTE: The use of SMS in MME by an operator that also deploys CS service on GERAN or UTRAN may lead to increased signalling traffic to the HSS. MPS priority treatment of SMS via MME for a UE with an MPS subscription is supported as described TS 23.401 [2]. C.2 Architecture As outlined in the architecture figure below SMS in MME requires support of SMS functionality in the MME and the MME also needs to receive SMS subscription information from the HSS. The SMS subscription information may be received through the S6a interface. Figure C.2-1: SMS in MME Architecture Figure C.2-2: SMS in MME architecture using IWF There is no impact on the UE and E-UTRAN. The SMS entities (including SMS router, etc.) functionality to support SMS in MME is the same as defined for reference point 2 and 3 in TS 23.040 [14] except the SGd and S6c interfaces use Diameter protocols as specified in TS 29.338 [43]. The interaction between SMS in MME and SMS over IP is described in TS 23.204 [15]. NOTE 1: The HSS may support both a Diameter S6c and a MAP C interface to SMS entities that have not evolved to S6c, or the SMS entities may support both interfaces to obtain routing information from HSS's that have not evolved to S6c. NOTE 2: According to TS 23.040 [14], the SMS-Router is optional and only required for MT SMS. C.3 Reference Points C.3.1 General The following reference points specifically enable support of SMS in MME. C.3.2 S6a In order to support "SMS in MME" the S6a shall allow the MME to request SMS subscription information and to register as a serving node for SMS. If the HSS supports this and has SMS subscription information available, it sends SMS subscription data to the MME. The SMS subscription data include for example the barring status of MO-SMS and MT-SMS and the MSISDN. If the HSS determines that the MME shall be deregistered for SMS, it shall indicate to the MME that it is not registered for SMS. C.3.3 S6c In order to support "SMS in MME" the Diameter based S6c shall allow the SMS central functions to request routing information from the HSS. C.3.4 SGd In order to support "SMS in MME" the Diameter based SGd shall provide the Short Message Relay Layer (SM-RL) between MME serving the UE and SMS central functions. C.4 Network Entities C.4.1 General The following network entities specifically enable support of SMS in MME C.4.2 MME The MME needs to support the following features: - UE-MME NAS procedures for SMS over SGs. - S6a functionality as described in clause C.3.2. - SMS procedures between UE and MME including support for the Short Message Control (SMC) and Short Message Relay (SM-RL) functions defined in TS 24.011 [28]. - Reporting UE's availability for receiving MT SMS to the HSS. - SMS functions including charging and Lawful Interception (LI). - Support combined EPS/IMSI procedures for "SMS-only" and in these: - provide a non-broadcasted LAI (not associated with any VLR); and - if needed provide a reserved TMSI that cannot cause any ambiguities with other TMSIs (e.g. when the UE changes to an area where it needs to derive SMS services from a GERAN/UTRAN MSC); and - indicate in the Attach/TAU Accept message that the IMSI attach is for "SMS-only"; and - notify the HSS it is capable of SMS transfer without the need of establishing an SGs association with an MSC; and - obtain SMS-related subscription information. - Support the registration procedures for SMS in MME described in clause C.8. - Support for Service Gap Control for MO SMS as specified in clause 4.3.17.9 of TS 23.401 [2]. - Support MPS priority treatment (e.g. determining the DRMP value in the messages related to SMS delivery, Paging Priority setting when paging is triggered for UE in CM-IDLE mode) for SMS delivery based on MPS for Messaging indication in HSS data and upon receipt of an MT-SMS from the SMS-GMSC marked with a DRMP associated with MPS for Messaging. C.4.3 HSS When an MME registers via the S6a including a registration for SMS Request, the HSS registers the MME as an MSC for MT SMS (i.e. in response to Send Routing Information (SRI) for SM the MME identity is passed back to the SMS‑GMSC/SMS router) when the HSS supports and decides to use SMS in MME. This registration as an MSC for MT SMS causes the HSS to cancel any old registered MSC. See clause C.8 for the detailed registration procedures. If the HSS receives a SRI for other CS Services than SMS it shall treat the UE as if it was detached from the CS domain. If the UE subsequently registers with an MSC for CS services, the HSS needs to replace the MME with the new MSC as the destination for SMS (but this is not a reason to cancel the MMEs registration for EPS Services). NOTE 1: That an HSS that supports SMS in MME registers the MME as an MSC for MT SMS does not affect how the information is stored in the HSS, however the HSS reuses the MNRF flag intended for the controlling SM delivery via the MSC, for controlling the SM delivery via MME. It only affects what serving node identities are returned in response to SRI for SM. In such cases the MME identity is passed back to the SMS-GMSC/SMS router where usually the MSC identity is sent. NOTE 2: For the PS and SMS only service to work also for outbound roamers, the 3GPP LTE-only operator may need to configure CS subscription data for SMS services in its HSS as a visited PLMN may deploy SMS over SGs. It may also use an IWF for MAP and Diameter translation. The 3GPP 2G/3G/LTE operator may need to upgrade its HSS to ensure that its outbound roamers get SMS services as a VPLMN may deploy only SMS in MME. An HSS allows an operator to configure a subscription, which is limited to only PS domain services and to SMS service via the CS and the PS domain. This limitation is indicated in the PS subscription data as "PS and SMS only". NOTE 3: The limitation of a subscription to only PS and SMS services can for example be based on an operator agreement with an MTC service provider, that only PS resources shall be used whenever possible. When an HSS supports "SMS in MME", i.e. provides all HSS functionality described for "SMS in MME", and the operator configured the HSS to apply that functionality, the HSS indicates "SMS in MME Support" in the data provided to an MME. NOTE 4: This separate handling of SMS subscriber data in the MME is also for aligning with the deployment option of an IWF for S6a that combines PS subscriber data with SMS subscriber data from CS subscriber data, where the data part that stems from CS subscriber data may be cancelled in MME independently from PS subscriber data. When the PS subscriber data are cancelled then any UE related subscriber data are cancelled in the MME. If the HSS determines that an MME shall be deregistered for SMS (e.g. because of a removal of SMS subscription, CS location update, etc), the HSS shall indicate to the MME that it is not registered for SMS. The HSS data, as in clause C.7.1, may include the MPS for Messaging indication parameter if the parameter is provisioned by an AS (as specified in TS 23.682 [48]) or by an operator. The HSS provides the parameter to the MME and to the SMS-GMSC/SMS router/IP-SM-GW when the HSS responds to an SMS routing information request. C.4.4 SMS-GMSC The SMS-GMSC needs to: - Support MPS priority treatment (e.g. determining the DRMP value in the messages related to SMS delivery) for SMS delivery based on the MPS for Messaging indication from the HSS, or based on a priority indication with the SMS message from the SMS Service Centre, if any. NOTE: How the SMS Service Centre provides the priority indication to the SMS-GSMC is outside the scope of this specification. C.5 Roaming considerations The SMS in MME architecture is an optional architecture enhancement for operators that wish to avoid to the use of MSC and SGs and do not provide Fallback to 3GPP CS services over GERAN or UTRAN. To support inbound roamers from networks that do not support the provision of SMS subscription information over S6a there are different options to provide interworking, e.g.: - SMS over SGs. - Use of an interworking function to convert between the S6a with SMS subscription data and S6a without SMS subscription data and D for SMS subscription. When the MME sends Ready for SM message to HSS for UE reachability notification, the interworking function also needs to convert the Ready for SM message transferred via the S6a interface to Ready for SM message transferred via the D interface. Operators that do not deploy the SMS in MME architecture option are not required to support the S6a enhancements in the HSS or the MME. C.6 Unsuccessful Mobile-Terminated SMS Transfer The MME or the HSS may not be able to deliver the SM to the UE. This can for example happen when the UE is not attached to EPS, when the UE's SMS memory capacity is exceeded, or when the Mobile-terminated SMS is barred. When the MME cannot deliver the SM to the UE, the MME shall return a failure report to the SMS GMSC/SMS router. The SMS-GMSC/SMS router/HSS procedures for handling the failure report are specified in TS 23.040 [14]. Additionally, if the SM failed due to the UE not being reachable, the MME shall set the Mobile-Not-Reachable-Flag-in-MME-for-SMS (MNRF-MME) indication in the MME. If the UE is using extended idle mode DRX with a DRX cycle value or if the UE is in PSM (as defined in TS 23.682 [48]) that can cause mobile terminating SMS retransmissions, the MME may return a failure report to the SMS GMSC/SMS router while still paging the UE. The MME shall set the Mobile-Not-Reachable-Flag-in-MME-for-SMS (MNRF-MME) indication in the MME. If the UE subsequently becomes reachable and MNRF-MME indication is set, the MME shall send a Ready for SM (IMSI, UE-Present) message to the HSS and the MME shall clear the corresponding MNRF-MME indication for that UE. NOTE: In the case that MME receives an indication from S‑GW that the UE has handover to non-3GPP coverage, it will not trigger this activity notification. If the UE subsequently notifies the MME that SMS memory is available, the MME shall send a Ready for SM (IMSI, UE-Memory-Available) message to the HSS. Reception of a Ready for SM message or an Update Location Request message by the HSS when MNRF is set, shall trigger the SMS alert procedure as defined in TS 23.040 [14]. C.7 Information storage C.7.1 HSS The following table specifies the HSS data defined per UE to support SMS in MME. Table C.7.1-1: HSS data Field Description SMS Subscription Parameters SMS subscription parameters, e.g. SMS teleservice, SMS barring list. Network Access Mode (NAM) Indicates whether the subscription includes subscriber data allowing for accessing PS and or CS domain. NOTE 2 PS and SMS only Indicates a subscription which is limited to PS domain services and to SMS service via the CS and the PS domain. NOTE 2 MME Registered for SMS Indicates that MME has been registered for SMS in the HSS MPS for Messaging Indicates whether the user has MPS for Messaging set (enabled)/cleared (disabled) as described in clause C.1. This MPS for Messaging indication parameter is valid only when the MPS-EPS-Priority bit is set. NOTE 1: When the UE is not reachable in the MME, the HSS sets the MNRF in the Message Waiting Data (MWD) since the MME is registered as an MSC. NOTE 2: If "PS and SMS only" is set for this subscriber, NAM is set to "CS+PS". When the HSS functionality for "SMS in the MME" is enabled, the HSS will include an "SMS in MME" feature indication along with the UE subscription information to the MME. C.7.2 MME The following table specifies the MME data defined per UE to support SMS in MME. Table C.7.2-1: MME Context for SMS Field Description SMS Subscription Data SMS subscription parameters, e.g. SMS teleservice, SMS barring list. MME Registered for SMS Indicates that MME has been registered for SMS in the HSS MNRF-MME Indicates whether activity from the UE shall be reported to the HSS. Network Access Mode (NAM) Indicates whether the subscription includes subscriber data allowing for access to PS and or CS domain. NOTE 1 PS and SMS only Indicates a subscription which is limited to PS domain services and to SMS service via the CS and the PS domain. NOTE 1 SMS in MME Support Capability of the HSS to support the SMS in MME feature MPS for Messaging Indicates whether the user has MPS for Messaging set (enabled)/cleared (disabled) as described in clause C.1. This MPS for Messaging indication parameter is valid only when the MPS-EPS-Priority bit is set. NOTE 1: If "PS and SMS only" is set for this subscriber, NAM is set to "CS+PS". C.8 Registration of MME for SMS C.8.1 Request for registration An MME supporting SMS in MME that needs to perform a registration with HSS shall follow the following procedure to become registered by the HSS also for SMS. The following sequence shows the request for registration with the HSS for SMS in MME. Figure C.8.1-1: MME registration for SMS 1. The UE initiates combined attach or combined TA/LA Update to an MME. A UE that only supports NB-IoT (see TS 23.401 [2]) may issue an EPS attach or TA Update instead of a combined attach or combined TA/LA Update. 2. The MME sends a Location Update Request (SMS in MME feature flag, MME address for MT-SMS routing, RegistrationForSMSRequest, "SMS-only" Indication) message to HSS. SMS in MME feature flag indicates that the MME is capable of SMS transfer without the need of establishing an SGs association with an MSC. The "SMS-only" Indication is included if it has been included in the request from the UE. The MME includes one of the following RegistrationForSMSRequest values based on the criteria shown in Table C.8.1-1. Table C.8.1-1: Registration For SMS Request values Value Description SMS in MME Required - MME does not support SGs; or - The MME can be configured to use this value when the UE indicates "SMS only" or when known that the subscription is "PS and SMS only". NOTE 1 SMS in MME Not Preferred - The MME can be configured to use this value when the UE indicates "SMS only" or when known that the subscription is "PS and SMS only" - The MME can be configured to use this value when the UE does not indicate "SMS only" (i.e. requests CSFB) and the MME has no subscriber data yet (when MME is configured to use SGs for "SMS and PS only" subscription). NOTE 2 No Preference for SMS in MME - The MME has no preference configured to use SMS in MME or SGs, but both options are available from MME perspective. NOTE 2 NOTE 1: If this is set the HSS cannot determine whether the SGs is available. NOTE 2: If this value is set it means that the MME supports SGs. UE might or might not indicate "SMS-only". 3. If the HSS supports SMS in MME and the subscription includes SMS: a) if one or more of the following is true: - Network Access Mode is PS only; or - the MME indicates "SMS in MME Required"; then the HSS shall register the MME for SMS; b) if the MME indicates "No Preference for SMS in MME" and Network Access Mode is not equal to PS only but one or more of the following are true: - the UE indicated "SMS-only"; - the subscription is limited to PS domain services and SMS service via the CS and the PS domain ("PS and SMS only"); then the HSS should register the MME for SMS; NOTE 3: The HSS can decide not to register the MME for SMS since it knows that the MME supports SGs but the normal behaviour would be to register for SMS and avoid an SGs association. c) if the MME indicates "SMS in MME Not Preferred" and Network Access Mode is not equal to PS only then the HSS should not register the MME for SMS; NOTE 4: The HSS can decide to register the MME for SMS based on the "PS and SMS only" setting and also on other factors including the UE indication for "SMS-Only", it is however assumed the normal behaviour would be not to register for SMS. d) otherwise the HSS shall not register the MME for SMS. If HSS registered the MME for SMS, the HSS stores the MME address for MT SMS. 4. If the HSS accepts to register the MME identity as an MSC identity for terminating SMS services then the HSS cancels the MSC/VLR registration from the HSS. 5. The HSS sends a Location Update Answer (indication whether the MME has been registered for SMS, subscription data including the Network Access Mode and "PS and SMS only" indications, SMS subscription data, MPS for Messaging indication, SMS in MME feature flag) message to MME. If the HSS does not register the MME for SMS, it shall indicate that the MME has not been registered for SMS and not include any SMS subscription data. SMS in MME feature flag indicates that the HSS is capable of supporting the SMS in MME feature. The MME stores the returned data and checks the result of registering the MME for SMS. If the registration for SMS was not accepted, the MME does following: a. For a PS-only subscription (i.e. the Network Access Mode in the subscription equals "PS-only"), the MME shall not establish any SGs association (no SMS services are provided to the UE). b. For a "PS and SMS only" subscription where SMS can be provided over CS (i.e. the Network Access Mode equals "PS+CS" and the subscription parameter "PS and SMS only" is set), the MME tries to establish SGs for SMS. c. For a PS and CS subscription where also other CS services are allowed (i.e. Network Access Mode equals "PS+CS" and the subscription parameter "PS and SMS only" is not set), the MME tries to establish SGs for SMS and other CS services. If the registration for SMS was accepted: - The HSS uses the Insert Subscriber Data procedure to inform the MME of changes in MPS for Messaging indication. - If the MPS for Messaging indication is set (enabled), the HSS sets Diameter priority and DSCP on responses on the S6a and S6c interfaces with values that are appropriate for MPS. - The SMS-GMSC obtains the MPS for Messaging indication in the Send Routing Information for SM from the HSS. If the MPS for Messaging indication is set (enabled) and /or when the SMS Service Centre sends a message with a priority indication (see clause C.4.4), the SMS-GMSC sets the Diameter priority and DSCP for SMS messages to values that are appropriate for MPS. - MME and SMS-GMSC set the Diameter priority and DSCP for SMS messages on the SGd interface to values that are appropriate for MPS. C.8.2 Removal of registration of MME for SMS C.8.2.0 General The removal of the registration of MME for SMS is used by: - The HSS to inform the MME that the registration of MME for SMS is cancelled; or by - The MME to inform the HSS that it requests to remove its registration for SMS. C.8.2.1 HSS-initiated removal of registration of MME for SMS When the HSS needs to indicate to the MME that it is no longer registered for SMS, (e.g. because of a removal of SMS subscription, CS location update, etc), the following procedure is applied. Figure C.8.2-1: Cancellation of MME registration for SMS in MME 1. There is an event that shall trigger the cancellation of the MME being registered for SMS. This may for example be the removal of the SMS subscription for the UE, a CS location update, etc. 2. The HSS sends an Insert Subscriber Data Request (Remove SMS registration) message to the MME to inform the MME that it is no more registered for SMS in MME. 3. The MME sets its "MME Registered for SMS" parameter as not registered for SMS and the "SMS subscription data" is considered by the MME as invalid. It acknowledges with an Insert Subscriber Data Answer message to the HSS. NOTE: A normal Cancel Location of MME which results in the MME no longer being registered for PS services for that UE will also render the MME not registered for SMS. C.8.2.2 MME-initiated removal of registration of MME for SMS When the MME needs to indicate to the HSS that it is no longer registered for SMS in HSS, (e.g. because the UE initiated a EPS attach only, TAU), the following procedure is applied. Figure C.8.2-2: Removal of MME registration for SMS in HSS 1. There is an event that triggers the cancellation of the MME being registered for SMS. This may for example be an UE initiated EPS attach only or a TAU. 2. The MME sends a message to the HSS to inform the HSS to remove its registration for SMS in HSS. 3. The HSS cancels the SMS registration for the UE in the MME. It acknowledges and responds to the MME. Annex D (informative): Change history Change history Date TSG # TSG Doc. CR Rev Cat Subject/Comment New 2010-06 SP-48 SP-100444 0218 4 B CSFB triggered by LCS while UE is in active VoIP session 10.0.0 2010-09 SP-49 SP-100531 0596 - A Removing UE rejection on CLI for 1x MT call 10.1.0 2010-09 SP-49 SP-100531 0609 - A Correction to the paging issue for CS fallback capable UEs in NMO II or III 10.1.0 2010-09 SP-49 SP-100541 0575 1 A Correction to Paging in MT CSFB 10.1.0 2010-09 SP-49 SP-100541 0577 1 A CS domain access rights handling in CSFB 10.1.0 2010-09 SP-49 SP-100541 0585 1 A Suspend clarification for CSFB 10.1.0 2010-09 SP-49 SP-100544 0580 3 B eMPS CR for CSFB (reference, definition and overall description) 10.1.0 2010-09 SP-49 SP-100544 0581 2 B eMPS CR for CSFB (attach procedure) 10.1.0 2010-09 SP-49 SP-100544 0582 2 B eMPS CR for CSFB (Mobile Originating Call) 10.1.0 2010-09 SP-49 SP-100544 0583 2 B eMPS CR for CSFB (Mobile Terminating Call) 10.1.0 2010-09 SP-49 SP-100544 0597 1 B MPS Support for 1xCSFB – Intro and impacts to Network Elements 10.1.0 2010-09 SP-49 SP-100544 0598 1 B MPS 1xCSFB impacts on MO and MT calls 10.1.0 2010-09 SP-49 SP-100558 0589 2 F MSC reselection in case of roaming restriction 10.1.0 2010-09 SP-49 SP-100558 0599 2 C Adding e1xCSFB support for dual Rx/Tx UE 10.1.0 2010-12 SP-50 SP-100681 0587 7 A Multiple PLMNs selection in eNodeB 10.2.0 2010-12 SP-50 SP-100691 0591 2 F Clarification of CSFB indication in Extended Service Request 10.2.0 2010-12 SP-50 SP-100691 0614 2 F UE behaviour with ISR active after CSFB with suspended PS bearers 10.2.0 2010-12 SP-50 SP-100691 0618 6 C Correction to CSFB MO flow 10.2.0 2010-12 SP-50 SP-100681 0620 1 A Clarification on CSFB in idle mode 10.2.0 2010-12 SP-50 SP-100681 0622 2 A Clarification on PLMN selection for CSFB 10.2.0 2010-12 SP-50 SP-100709 0629 1 F MTC related NNSF in MME for SMS over SGs 10.2.0 2010-12 SP-50 SP-100681 0636 2 A Correction to Abnormal Service Reject Procedure 10.2.0 2010-12 SP-50 SP-100681 0642 - A CSFB with Release with Redirection to UMTS and 'deferred SIB reading' 10.2.0 2011-01 - - - - - Update of LTE logo to LTE-Advanced logo 10.2.1 2011-03 SP-51 SP-110059 0643 - A Correction on CLI in page message for 1x MT call 10.3.0 2011-03 SP-51 SP-110064 0646 1 A S102 Redirection Timing 10.3.0 2011-03 SP-51 SP-110076 0648 2 F CS PLMN reselection requirement for CSFB and RAT/LA checking 10.3.0 2011-03 SP-51 SP-110064 0651 3 A PS Suspending Clarification 10.3.0 2011-03 SP-51 SP-110064 0656 1 A SMS-CSFB cell ID reporting correction 10.3.0 2011-03 SP-51 SP-110076 0660 1 F Correction about the paging area in case of no available stored TAI list in MME 10.3.0 2011-03 SP-51 SP-110064 0663 1 A 3GPP2 alignment for 1xCSFB MT 10.3.0 2011-03 SP-51 SP-110076 0665 3 F 3GPP2 alignment for 1xCSFB SMS MT 10.3.0 2011-03 SP-51 SP-110064 0671 2 A CSFB procedures for other types of CS services 10.3.0 2011-03 SP-51 SP-110064 0673 - A Correction to CSFB NACC/CCO 10.3.0 2011-03 SP-51 SP-110076 0674 3 B Introduction of MT Roaming Forwarding for CSFB 10.3.0 2011-04 - - - - - MCC Correction to History table version numbers 10.3.1 2011-06 SP-52 SP-110330 0658 5 F Correction to CSFB procedure for UEs with LIPA PDN connections only 10.4.0 2011-06 SP-52 SP-110335 0666 3 F Updating dual rx/tx e1xCSFB to use explicit UE support indicator 10.4.0 2011-06 SP-52 SP-110335 0681 2 F RRC release with system information clarification 10.4.0 2011-06 SP-52 SP-110327 0684 4 F Priority for terminating CSFB sessions for eMPS 10.4.0 2011-06 SP-52 SP-110330 0686 3 F Interaction between LIPA and CSFB service 10.4.0 2011-06 SP-52 SP-110335 0689 - F Correct detach procedure with ISR activated 10.4.0 2011-06 SP-52 SP-110324 0691 - A Correction of PS suspension procedure in CSFB to GERAN A/Gb mode 10.4.0 2011-06 SP-52 SP-110324 0694 1 A Correction of CSFB Paging to avoid the use of TMSI 10.4.0 2011-09 SP-53 SP-110456 0702 2 A Clarification about suspend and resume handling 10.5.0 2011-12 SP-54 SP-110738 0706 4 F Handling of SGs paging in VLR and MME failure cases 10.6.0 2011-12 SP-54 SP-110738 0709 2 F VLR SGs paging retry 10.6.0 2011-12 SP-54 SP-110738 0710 3 F Fast Return after CSFB 10.6.0 2011-12 SP-54 SP-110733 0714 1 A Correction of CSFB Paging procedure in MME 10.6.0 2011-12 SP-54 SP-110733 0717 2 A Separate LAU and RAU procedures in CS fallback procedure 10.6.0 2012-03 SP-55 SP-120068 0725 2 A Clarification of LAU/RAU trigger for CSFB UE when ISR is activated 10.7.0 2012-03 SP-55 SP-120066 0722 1 A Clarification of ISR activation condition for NMO II RAU and Periodic RAU 10.7.0 2012-03 SP-55 SP-120066 0750 1 A Correction of system behaviour upon MME implicit detach timer expiry when SGs is associated and ISR is activated 10.7.0 2012-03 SP-55 SP-120075 0703 3 F CM Service Request during MO-LR procedure 10.7.0 2012-03 SP-55 SP-120075 0736 1 F Corrections to SGs paging for CSFB 10.7.0 2012-03 SP-55 SP-120088 0705 2 F Clarification about ISR maintenance for CSFB 11.0.0 2012-03 SP-55 SP-120088 0727 1 F Clarification of detach procedure when ISR is activated 11.0.0 2012-03 SP-55 SP-120088 0729 - F Correction of reference 11.0.0 2012-03 SP-55 SP-120088 0735 1 F Clarification about PLMN selection for CS domain 11.0.0 2012-03 SP-55 SP-120086 0743 1 B ISR deactivation exception for PS only SMS 11.0.0 2012-03 SP-55 SP-120086 0746 3 B SMS over SGs usage to support NAS procedures for PS only SMS 11.0.0 2012-06 SP-56 SP-120239 0760 2 F Clarifying the feature definition for SMS in MME 11.1.0 2012-06 SP-56 SP-120239 0761 7 F Correction of SMS in MME related Cancellation Processes 11.1.0 2012-06 SP-56 SP-120240 0764 6 F UE Availability for SMS 11.1.0 2012-06 SP-56 SP-120237 0766 1 A Handling of SMS over SGs in case of absent LAI 11.1.0 2012-06 SP-56 SP-120237 0772 2 A Correction for downlink unreachable due to wrong suspending 11.1.0 2012-06 SP-56 SP-120232 0793 2 A Correction of system behaviour upon PGW initiated last PDP Context Deactivation when SGs is associated and ISR is activated 11.1.0 2012-06 SP-56 SP-120237 0795 4 A Partial VLR failure or VLR restart with CSFB and ISR 11.1.0 2012-06 SP-56 SP-120246 0797 1 B Taking UE support/non-support of GERAN network sharing into account in CSFB 11.1.0 2012-06 SP-56 SP-120240 0801 1 F Update to SMS in MME Architecture reference points 11.1.0 2012-06 SP-56 SP-120251 0822 1 F Alignment with stage 3 for the condition to deactivate ISR by the SGSN 11.1.0 2012-09 SP-57 SP-120486 0726 4 F SGs Support for MSC in Pool to avoid dual VLR registration. 11.2.0 2012-09 SP-57 SP-120482 0809 3 F Clarification on ISR and 'SMS in MME' 11.2.0 2012-09 SP-57 SP-120482 0830 4 F Correction of PS-only Feature Description 11.2.0 2012-09 SP-57 SP-120482 0834 1 F SMS in MME consolidated description and updated scope 11.2.0 2012-09 SP-57 SP-120485 0836 - C Removing NMO-III 11.2.0 2012-12 SP-58 SP-120722 0810 6 F Network sharing impact on the CSFB 11.3.0 2012-12 SP-58 SP-120717 0839 3 F Registration of MME for SMS 11.3.0 2012-12 SP-58 SP-120713 0846 1 A Suitable cell selected after CSFB 11.3.0 2013-03 SP-59 SP-130085 0848 - F Correction of when the MME shall send the CS domain operator to the VLR in case of network sharing 11.4.0 2013-03 SP-59 SP-130081 0850 - A Correction to enhanced CSFB to 1xRTT 11.4.0 2013-03 SP-59 SP-130080 0856 - A Priority setting for 1xCSFB correction 11.4.0 2013-06 SP-60 SP-130305 0847 3 F Clarification on "SMS in MME" 11.5.0 2013-06 SP-60 SP-130241 0863 2 A LAU-less Emergency call with CSFB 11.5.0 2013-06 SP-60 SP-130309 0868 2 F Enabling terminating CS services for EPS/IMSI attached UE selecting a non-3GPP access 11.5.0 2013-06 SP-60 SP-130211 0871 4 A CSFB interactions with IMS Emergency call 11.5.0 2013-06 SP-60 SP-130223 0872 3 F Release of SGs association in case of SRVCC 11.5.0 2013-06 SP-60 SP-130224 0873 2 F Handling of terminating CS services during IMS Call 11.5.0 2013-06 SP-60 SP-130320 0874 3 F How CSFB UE return back to the former LTE PLMN 11.5.0 2013-06 SP-60 SP-130320 0875 2 F Clarification for MME selection during NW-initiated CS Service procedure while UE is in IMS VoIP session 11.5.0 2013-06 SP-60 SP-130320 0877 2 F CN signalling for allowing UE return to former LTE PLMN after CSFB 11.5.0 2013-06 SP-60 SP-130212 0879 1 A MSC/VLR selection for MTC devices 11.5.0 2013-09 SP-61 SP-130370 0881 1 F SMS in MME and SMS over IP 11.6.0 2013-09 SP-61 SP-130376 0882 1 F Improve how CSFB UE return back to the former LTE PLMN 11.6.0 2013-09 SP-61 SP-130376 0883 2 D Correction on 1xCSFB IMS interaction 11.6.0 2013-09 SP-61 SP-130376 0889 2 F TMSI reallocation for CSFB/emergency handling with IMSI 11.6.0 2013-09 SP-61 SP-130368 0892 1 A ISR with CSFB/ emergency handling with IMSI 11.6.0 2013-09 SP-61 SP-130376 0893 2 F Corrections to UE return to last used LTE PLMN after CSFB 11.6.0 2013-09 SP-61 SP-130362 0880 3 F Fix CSFB MT call failure due to HO 11.6.0 2013-09 SP-61 SP-130385 0885 2 C Adding a recommendation on hysteresis mechanism for WORM feature 12.0.0 2013-12 SP-62 SP-130533 0861 7 C Call Independent supplementary services with CSFB 12.1.0 2013-12 SP-62 SP-130525 0896 2 A Earlier provision of the former last used LTE PLMN ID 12.1.0 2013-12 SP-62 SP-130525 0897 2 A SS service ID used in the Paging message 12.1.0 2013-12 SP-62 SP-130522 0899 1 A MME initiated removal of registration of MME for SMS 12.1.0 2013-12 SP-62 SP-130526 0900 2 F Correction of the extended service request procedure for LIPA and SIPTO@LN 12.1.0 2013-12 SP-62 SP-130525 0901 - A Correction of resume procedure after CSFB 12.1.0 2013-12 SP-62 SP-130525 0903 1 A CS MO indication to VLR via SGs 12.1.0 2013-12 SP-62 SP-130540 0907 2 F Resuming PS services that have been handed over to non-3GPP 12.1.0 2014-03 SP-63 SP-140098 0918 - A Supporting priority services in 1xCSFB 12.2.0 2014-03 SP-63 SP-140111 0919 - F Correction of MT procedures in active mode 12.2.0 2014-06 SP-64 SP-140250 0925 3 A Correction of CSFB priority and eMLPP handling 12.3.0 2014-06 SP-64 SP-140256 0927 1 A How to transfer the last used LTE PLMN identity for CSFB to UTRAN 12.3.0 2014-06 SP-64 SP-140251 0930 1 A Correction on priority paging 12.3.0 2014-06 SP-64 SP-140377 0931 1 F New CSFB high priority indication for eMPS and emergency call 12.3.0 2014-06 SP-64 SP-140377 0932 - F Correction of ISR requirements for SGSN 12.3.0 2014-06 SP-64 SP-140252 0935 1 A Handling CSFB request when VoLTE call is on-going in non SRVCC capable network/UE 12.3.0 2014-09 SP-65 SP-140425 0938 - F Corrections to message names 12.4.0 2015-03 SP-67 SP-150109 0941 2 F Paging without LAI 12.5.0 2015-06 SP-68 SP-150224 0946 - A Correction of CSFB references for CS domain priority schemes 12.6.0 2015-06 SP-68 SP-150239 0939 6 C Enable ISR for PS-only UE 13.0.0 2015-09 SP-69 SP-150501 0947 2 B Mobile Terminating SMS handling for extended I-DRX 13.1.0 2015-12 SP-70 SP-150614 0953 2 F Correction of references to parts of Detach procedures 13.2.0 2015-12 SP-70 SP-150611 0954 1 F MT-SMS triggered Paging handling for extended DRX UE 13.2.0 2015-12 SP-70 SP-150614 0955 1 F Correction on condition of CSFB MO 13.2.0 2016-03 SP-71 SP-160161 0961 1 B SMS support with EPS attach and TAU 13.3.0 2016-06 SP-72 SP-160289 0956 4 B MT SM retransmission by the SMS GMSC to a UE in eDRX at the time requested in the Delivery Report 13.4.0 2016-06 SP-72 SP-160289 0957 4 B Prioritized SM retransmission by the SMS SC when the UE becomes reachable 13.4.0 2016-06 SP-72 SP-160289 0960 4 B MT SM transmission to a UE in eDRX within the SM-Delivery-Start-Time/Timer 13.4.0 2016-06 SP-72 SP-160435 0964 2 F Support for SMS using CP optimisation for CIOT 13.4.0 2016-06 SP-72 SP-160289 0956 4 B MT SM retransmission by the SMS GMSC to a UE in eDRX at the time requested in the Delivery Report 13.4.0 2016-06 SP-72 SP-160289 0957 4 B Prioritized SM retransmission by the SMS SC when the UE becomes reachable 13.4.0 2016-06 SP-72 SP-160289 0960 4 B MT SM transmission to a UE in eDRX within the SM-Delivery-Start-Time/Timer 13.4.0 2016-06 SP-72 SP-160435 0964 2 F Support for SMS using CP optimisation for CIOT 13.4.0 2017-03 - - - - - Update to Rel-14 version (MCC) 14.0.0 2017-09 SP-77 SP-170714 0969 1 A Alignment with stage 3 on handling of Mobile Terminating SMS handling for extended I-DRX 14.1.0 2017-09 SP-77 SP-170723 0970 2 F Correction on combined attach for NB-IoT UE for TS 23.272 in R14 14.1.0 2017-12 SP-78 SP-170910 0972 2 A Alignment with stage 3 of HLCOM aspect on Mobile Terminating SMS handling 14.2.0 2017-12 SP-78 SP-170724 0973 1 B Introduction of Service Gap Control 15.0.0 2020-07 SP-88E - - - - Update to Rel-16 version (MCC) 16.0.0 2021-09 SP-93E SP-210932 0974 - F Reject Paging for CS domain paging 17.0.0 2024-03 - - - - - Update to Rel-18 version (MCC) 18.0.0 2024-09 SP-105 SP-241266 0975 3 B MPS support for MO and MT SMS over NAS procedure 19.0.0 2024-12 SP-106 SP-241490 0976 2 F Priority at HSS and SMS-GMSC 19.1.0
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1 Scope
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The present document specifies the stage 2 of the service-based architecture used for location services in the 5G system, and corresponding Network Functions (NFs), NF services and procedures, to meet the service requirements defined in TS 22.261 [3] and TS 22.071 [2].
Location Services specified in the present document include regulatory location services and commercial location services. The architecture and signalling procedures in NG-RAN are defined in TS 38.305 [9].
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2 References
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The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or non‑specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 22.071: "Technical Specification Group Systems Aspects; Location Services (LCS)".
[3] 3GPP TS 22.261: "Service requirements for the 5G system; Stage 1".
[4] 3GPP TS 23.271: "Functional stage 2 description of Location Services (LCS)".
[5] 3GPP TS 43.059: "Functional Stage 2 description of Location Services in GERAN".
[6] Void.
[7] 3GPP TS 36.305: "Stage 2 functional specification of User Equipment (UE) positioning in E-UTRAN".
[8] 3GPP TS 23.032: "Universal Geographical Area Description (GAD)".
[9] 3GPP TS 38.305: "Stage 2 functional specification of User Equipment (UE) positioning in NG-RAN".
[10] 3GPP TS 23.167: "IP Multimedia Subsystem (IMS) emergency sessions".
[11] 3GPP TS 24.501: "Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3".
[12] 3GPP TS 29.572: "5G System; Location Management Services; Stage 3".
[13] OMA MLP TS: "Mobile Location Protocol", [http://www.openmobilealliance.org].
[14] Void.
[15] 3GPP TS 38.455: "NG-RAN; NR Positioning Protocol A (NRPPa)".
[16] 3GPP TS 29.518: "5G System; Access and Mobility Management Services; Stage 3".
[17] 3GPP TS 25.305: "Stage 2 functional specification of User Equipment (UE) positioning in UTRAN".
[18] 3GPP TS 23.501: "System Architecture for the 5G System; Stage 2".
[19] 3GPP TS 23.502: "Procedures for the 5G System; Stage 2".
[20] 3GPP TS 37.355: "LTE Positioning Protocol (LPP)".
[21] 3GPP TS 23.316: "Wireless and wireline convergence access support for the 5G System (5GS)".
[22] Void.
[23] ITU-T Recommendation E.164: "The international public telecommunication numbering plan".
[24] 3GPP TS 23.222: "Common Application Programming Interface (API) framework for 3GPP northbound APIs".
[25] RFC 2396: "Uniform Resource Identifiers".
[26] RFC 3261: "SIP: Session Initiation Protocol".
[27] 3GPP TS 23.228: "IP multimedia subsystem (IMS)".
[28] 3GPP TS 23.003: "Numbering, addressing and identification".
[29] 3GPP TS 29.002: "Mobile Application Part (MAP) specification".
[30] 3GPP TS 32.271: "Telecommunication management; Charging management; Location Services (LCS) charging".
[31] 3GPP TS 32.298: "Telecommunication management; Charging management; Charging Data Record (CDR) parameter description".
[32] Void.
[33] 3GPP TS 29.571: "5G System; Common Data Types for Service Based Interfaces; Stage 3".
[34] Void.
[35] 3GPP TS 29.122: "T8 reference point for Northbound APIs".
[36] 3GPP TS 24.571: "5G System (5GS); Control plane Location Services (LCS) procedures; Stage 3".
[37] 3GPP TS 23.288: "Architecture enhancements for 5G System (5GS) to support network data analytics services".
[38] 3GPP TS 38.413: "NG-RAN; NG Application Protocol (NGAP)".
[39] 3GPP TS 22.104: "Service requirements for cyber-physical control applications in vertical domains".
[40] 3GPP TS 23.586: "Architectural Enhancements to support Ranging based services and Sidelink Positioning".
[41] 3GPP TS 23.503: "Policy and charging control framework for the 5G System (5GS); Stage 2".
[42] 3GPP TS 23.632: "User data interworking, coexistence and migration; Stage 2".
[43] 3GPP TS 29.563: "Home Subscriber Server (HSS) services for interworking with Unified Data Management (UDM); Stage 3".
[44] 3GPP TS 33.536: "Security aspects of 3GPP support for advanced Vehicle-to-Everything (V2X) services".
[45] 3GPP TS 33.503: "Security Aspects of Proximity based Services (ProSe) in the 5G System (5GS)".
[46] 3GPP TS 33.533: "Security aspects of ranging based services and sidelink positioning".
[47] 3GPP TS 38.355: "Sidelink Positioning Protocol (SLPP)".
[48] 3GPP TS 24.572: " User Plane Location Services (LCS) Protocols And Procedures; Stage 3".
[49] OMA-AD-SUPL-V2_0: "Secure User Plane Location Architecture Approved Version 2.0".
[50] 3GPP TS 33.501: " Security architecture and procedures for 5G system".
[51] 3GPP TS 33.256: "Security aspects of Uncrewed Aerial Systems (UAS)".
[52] RFC 5985: "HTTP-Enabled Location Delivery (HELD)".
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3 Definitions and Abbreviations
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3.1 Definitions
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For the purposes of the present document, the terms and definitions given in TR 21.905 [1] and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].
5G enhanced positioning area: see TS 22.261 [3].
5G positioning service area: see TS 22.261 [3].
Backhaul PLMN (BH PLMN): see TS 23.501 [18].
LCS Client: entity that interacts with GMLC for the purpose of obtaining location information for one or more UEs. The LCS Client may reside in the UE.
For the purposes of the present document, the following terms and definitions given in TS 23.271 [4] apply:
Call Related: see TS 23.271 [4].
Codeword: see TS 23.271 [4].
Current Location: see TS 23.271 [4].
Deferred location request: see TS 23.271 [4].
DL Positioning: positioning of a target UE in which the target UE obtains downlink measurements for a 3GPP RAT.
GNSS Assistance Data: see clause 6.5.2.1 of TS 37.355 [20].
Immediate location request: see TS 23.271 [4].
Last Known Location: see TS 23.271 [4].
LCS (LoCation Services): see TS 23.271 [4].
LMF-based AI/ML Positioning: UE-assisted/LMF-based positioning with LMF-side model, and NG-RAN node assisted positioning with LMF-side model.
Local Co-ordinates: see TS 23.032 [8].
Local Location: location determined by Local Co-ordinate(s).
Located UE: see TS 23.586 [40].
Location Estimate: see TS 23.271 [4].
LOS/NLOS measurement indication: LOS-NLOS-Indicator as defined in TS 37.355 [20] or LOS/NLOS information as defined in TS 38.455 [15].
Positioning Reference Unit (PRU): see TS 38.305 [9].
Mobile Base Station Relay: see TS 23.501 [18].
Mobile gNB with Wireless Access Backhauling (MWAB): see TS 23.501 [18].
MWAB Broadcasted PLMN: see TS 23.501 [18].
PRU association: association of a PRU with an LMF by providing PRU related information to an LMF.
PRU dis-association: remove the PRU related information to dis-associate a PRU with an LMF.
Pseudonym: see TS 23.271 [4].
Pseudonym mediation device: Functionality that verifies pseudonyms to verinyms.
RAT Independent Positioning: positioning of a target UE in which the target UE obtains measurements not related to a 3GPP RAT.
Requestor: see TS 23.271 [4].
Requestor Identity: see TS 23.271 [4].
Response Method: for LCS Client using the OMA MLP protocol. Detail see TS 23.271 [4].
Scheduled Location Time: a future global time (e.g. UTC) at which a UE is to be located.
Service Type: see TS 23.271 [4].
Sidelink Positioning: see TS 23.586 [40]
Target UE: see TS 23.271 [4].
UL Positioning: positioning of a target UE in which NG-RAN obtains uplink measurements of the target UE for a 3GPP RAT.
UL+DL Positioning: positioning of a target UE using both DL Positioning and UL Positioning.
Velocity: see TS 23.271 [4].
Verinym: see TS 23.271 [4].
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3.2 Abbreviations
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For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905 [1].
APN Access Point Name
APN-NI APN Network Identifier
EDT Early Data Transmission
E-SMLC Evolved Serving Mobile Location Centre
GMLC Gateway Mobile Location Centre
HGMLC Home GMLC
LCS LoCation Services
LDR Location Deferred Request
LIR Location Immediate Request
LMF Location Management Function
LOS Line-Of-Sight
LPI LCS Privacy Indicator
LPHAP Low Power and High Accuracy Positioning
LRF Location Retrieval Function
MBSR Mobile Base Station Relay
MO-LR Mobile Originated Location Request
MT-LR Mobile Terminated Location Request
MWAB Mobile gNB with wireless access backhauling
NLOS Non-Line-Of-Sight
NI-LR Network Induced Location Request
PMD Pseudonym mediation device functionality
POI Privacy Override Indicator
PRU Positioning Reference Unit
SDT Small Data Transmission
TNAN Trusted Non-3GPP Access Network
TNAP Trusted Non-3GPP Access Point
TWAP Trusted WLAN Access Point
VGMLC Visited GMLC
SL-MO-LR Sidelink Mobile Originating Location Request
SL-MT-LR Sidelink Mobile Terminating Location Request
SUPL Secure User Plane Location
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4 Architecture Model and Concepts
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4.1 General Concepts
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A general description of location services and service requirements are given in the specification TS 22.071 [2] and TS 22.261 [3]. Support of location services for GERAN, UTRAN and E-UTRAN access networks is described in TS 23.271 [4], TS 43.059 [5], TS 25.305 [17] and TS 36.305 [7].
The positioning of a UE can be supported by RAT dependent position methods, which rely on for example 3GPP RAT measurements obtained by a target UE and/or on measurements obtained by an Access Network of 3GPP RAT signals transmitted by a target UE. Positioning of a UE can also be supported by RAT independent position methods which may rely on non-RAT measurements obtained by a UE and/or on other information.
The Location Services defined in this specification are applicable to PLMN(s) and within a SNPN as described in clause 6, except for the following features, which are not supported in SNPNs:
- interworking with EPC;
- roaming; and
- direct access to SNPN via non-3GPP access.
The Location Service in PNI-NPN with signalling optimisation is defined as clause 5.13.
The positioning of a UE can be performed by either 3GPP access network or non-3GPP access network. A proper access type shall be determined to assure that the positioning result can fulfil the requested QoS and operator policy.
Location information for one or multiple target UEs may be requested by and reported to an LCS client or an AF within or external to a PLMN or SNPN, or a control plane NF within a PLMN or SNPN. Location information contained in the location request and location information contained in the location response are defined in clause 5.5.
For location request from LCS client (neither in the UE nor in the NG-RAN) or AF external to a PLMN or SNPN, privacy verification of the target UE shall be enabled to check whether it is allowed to acquire the UE location information based on UE LCS privacy profile and whether the LCS client or the AF is authorised to use the location service as defined in clause 5.4. Additionally, UEs may optionally support privacy notification and verification on behalf of a user. Privacy override is also supported for regulatory LCS services according to local regulation.
The capabilities of a target UE to support LCS may be signalled by the UE to a serving PLMN or to an SNPN at the AS, NAS and application (positioning protocol) levels to enable use of position methods supported by the UE.
To provide Location Service in the EPC interworking scenario, an EPC and 5GC common interface shall be used for the location request from LCS client or AF.
Ranging based services and Sidelink Positioning for a UE can be supported, and details are described in clause 5.17.
4.1a Types of Location Request
4.1a.1 Network Induced Location Request (NI-LR)
With a Network Induced Location Request (NI-LR), a serving AMF for a UE initiates localization of the UE for a regulatory service (e.g. an emergency call from the UE) or for verification of a UE location (country or international area) for NR satellite access.
4.1a.2 Mobile Terminated Location Request (MT-LR)
With a Mobile Terminated Location Request (MT-LR), an LCS client or AF external to or internal to a serving PLMN sends a location request to the PLMN (which may be the HPLMN or VPLMN) for the location of a target UE.
4.1a.3 Mobile Originated Location Request (MO-LR)
With a Mobile Originated Location Request (MO-LR), a UE sends a request to a serving PLMN for location related information for the UE.
4.1a.4 Immediate Location Request
With an immediate location request, an LCS client or AF sends or instigates a location request for a target UE (or group of target UEs) and expects to receive a response containing location information for the target UE (or group of target UEs) within a short time period which may be specified using QoS. In regulatory cases, one or more responses of the target UE's location information can be expected. An immediate location request may be used for an NI-LR, MT-LR or MO-LR.
4.1a.5 Deferred Location Request
With a deferred location request, an LCS client or AF sends a location request to a PLMN for a target UE (or group of target UEs) and expects to receive a response containing the indication of event occurrence and location information if requested for the target UE (or group of target UEs) at some future time (or times), which may be associated with specific events associated with the target UE (or group of target UEs). In this version of the specification, only deferred location requests for an MT-LR are supported.
4.1a.5.1 Types of event
The following types of event are defined for a deferred location request.
a) UE availability: Any event in which the 5GCN has established a contact with the UE. This event is considered to be applicable when the UE is temporarily unavailable due to inaction by the user, or for temporarily loss of radio connectivity or IMSI detach and so on. The UE Available event only requires one response to an LCS client/AF and after this response, the UE Available event is concluded.
b) Area: An event where the UE enters, leaves or remains within a pre-defined geographical area. At least one type of area event can be defined (i.e. entering, leaving or remaining within the area). The LCS client or AF may define the target area as a geographical area or as a geopolitical name of an area. The PLMN may translate and define the target area as the identities of one or more radio cells or tracking areas. The LCS client or AF may request an additional check about whether the UE is located within the provisioned target area. The area event may be reported one time only, or multiple times. The area event report shall contain an indication of the event occurrence. The location estimate may be included in the report. If an area event is detected by the UE but an event report cannot be sent (e.g. because the UE cannot access the network or due to a minimum reporting interval), a report shall be sent later when possible irrespective of whether the area event still applies for the current UE location. Area event reporting is controlled by a minimum and a maximum reporting time. The minimum reporting time defines the minimum allowed time between successive area events. The maximum reporting time defines the maximum time between successive reports. When a UE sends a report due to expiration of the maximum reporting time, the UE indicates expiration of the maximum reporting time as the trigger event. The maximum reporting time enables the AF, LCS client and HGMLC to remain aware of continuing support by the UE for the area event (e.g. to detect if area event reporting may have been aborted due to UE power off).
NOTE: To achieve more precise usage of area event in some scenario, e.g. for small target area, it may be useful if LCS Client/AF requests UE location estimate and compares the location estimate with the target area.
c) Periodic Location: An event where a defined periodic timer expires in the UE and activates a location report. If a periodic event is detected by the UE but an event report cannot be sent (e.g. because the UE cannot access the network temporarily), a report shall be sent later when possible and the periodic timer for the next event shall then be started. The reporting duration for periodic location shall equal the requested number of reports multiplied by the periodic interval even when reports are delayed.
d) Motion: An event where the UE moves by more than some predefined straight line distance from a previous location. The motion event may be reported one time only, or multiple times. The motion event report shall contain an indication of the event occurrence. A location estimate may be included in the report if requested by the LCS client or AF. For successive motion event reports, motion is determined relative to the UE location corresponding to the immediately preceding event report (including an event report triggered by expiration of the maximum reporting time). If a motion event is detected by the UE but an event report is deferred (e.g. because the UE cannot access the network temporarily), a report shall be sent later when possible irrespective of whether the motion event still applies to the current UE location. Motion reporting is controlled by a minimum and a maximum reporting time. The minimum reporting time defines the minimum allowed time between successive event reports. The maximum reporting time defines the maximum time between successive reports. When a UE sends a report due to expiration of the maximum reporting time, the UE indicates expiration of the maximum reporting time as the trigger event. The maximum reporting time enables the AF, LCS client and HGMLC to remain aware of continuing support by the UE for the motion event (e.g. to detect if motion event reporting may have been aborted due to UE power off).
4.1b LCS Quality of Service
LCS Quality of Service is used to characterise the location request. It can either be determined by the operator or determined based on the negotiation with the LCS client or the AF. It is optional for LCS client or the AF to provide the LCS Quality of Service in the location request.
LCS Quality of Service information is characterised by 3 key attributes:
- LCS QoS Class as defined below.
- Accuracy: i.e. Horizontal Accuracy (see clause 4.3.1 of TS 22.071 [2]) and Vertical Accuracy (see clause 4.3.2 of TS 22.071 [2].
- Response Time (e.g. no delay, low delay or delay tolerant as described in clause 4.3.3 of TS 22.071 [2]).
NOTE 1: One or two QoS values for Horizontal Accuracy, Vertical Accuracy can be provided in the location request in addition to a preferred accuracy when LCS QoS Class is set to Multiple QoS Class.
The LCS QoS Class defines the degree of adherence by the Location Service to another quality of service parameter (Accuracy), if requested. The 5G system shall attempt to satisfy the other quality of service parameter regardless of the use of QoS Class. There are 3 LCS QoS Classes:
- Best Effort Class: This class defines the least stringent requirement on the QoS achieved for a location request. If a location estimate obtained does not fulfil the other QoS requirements, it should still be returned but with an appropriate indication that the requested QoS was not met. If no location estimate is obtained, an appropriate error cause is sent.
- Multiple QoS Class: This class defines intermediate stringent requirements on the QoS achieved for a location request. If the obtained location estimate does not fulfil the most stringent (i.e. primary) other QoS requirements affected by the degree of adherence of the QoS class, then another location estimation may be triggered at LMF attempting less stringent other QoS requirements. The process may be iterated until the least stringent (i.e. minimum) other QoS requirements are attempted. If the least stringent other QoS requirements cannot be fulfilled by a location estimate, then the location estimate shall be discarded, and an appropriate error cause shall be sent.
NOTE 2: An AF may provide a location request with Multiple QoS Class via NEF. For an LCS client to provide a location request with Multiple QoS Class an Le interface implementation supporting Multiple QoS Class may be required.
NOTE 3: Multiple QoS Class can only be applied for Deferred 5GC-MT-LR Procedure in this release of the specification.
- Assured Class: This class defines the most stringent requirement on the accuracy achieved for a location request. If a location estimate obtained does not fulfil the other QoS requirements, then it shall be discarded, and an appropriate error cause shall be sent.
NOTE 4: How the LMF decides the positioning method is an implementation aspect not pre-determined by QoS criteria.
For LCS client, it may indicate accuracy defined in TS 29.572 [12], tables 6.1.6.3.2-1 and 6.1.6.3.5-1. For AF, it may either indicate the accuracy defined in TS 29.572 [12], table 6.1.6.3.2-1, or indicate a particular value e.g. PLMN ID defined in TS 29.122 [35], table 5.3.2.4.7-1.
4.1c Scheduled Location Time
A scheduled location time allows an external LCS Client, AF or the UE to specify a time in the future at which a current location of the UE is to be obtained. A scheduled location time can be used with a 5GC-MT-LR, 5GC-MO-LR or deferred 5GC-MT-LR for periodic or triggered location events. The location preparation phase starts when a location related request is sent by an LCS Client, AF or UE requesting a current location of the UE. The request includes the scheduled location time T. As part of the location preparation phase, the 5GC, and UE interact to determine suitable position methods and schedule location measurements of the UE. The LMF coordinates the interaction and is aware of the scheduled location time. The location preparation phase ends at or near to the time T and is followed by a location execution phase in which the UE location is obtained and returned to the external LCS Client, AF or the UE.
A scheduled location time only applies when an external LCS Client, AF or the UE is aware of a specific time in the future at which the location of the UE is needed. A location estimate returned to an LCS Client, AF or UE for a scheduled location time can be treated by the LCS Client, AF or UE as an estimate of the location of the UE at the scheduled location time.
To support the Scheduled Location Time in 5GC-MO-LR, the UE defers sending the request to AMF until the time remaining until the scheduled location time is within some implementation dependent threshold in order to avoid failure triggered by HTTP request timeout.
When support the Scheduled Location Time in 5GC-MT-LR (i.e. the LCS Client/AF obtains one time UE location at Scheduled Location Time), to avoid failure triggered by HTTP request timeout, one of the following methods is applied:
- The LCS Client or AF defers sending the request until the time remaining until the scheduled location time is within some implementation dependent threshold; or
- Re-using the deferred 5GC-MT-LR for periodic location events procedure to realize providing one time UE location at Scheduled Location Time by, e.g. set the value of total reporting number parameter in the location request to one.
NOTE: Which method to be used is implementation specific.
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4.2 Architectural Reference Model
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4.2.1 Non-roaming reference architecture
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Figure 4.2.1-1 shows an architectural reference model for 5GS LCS for a non-roaming UE and PRU in reference point representation.
Figure 4.2.1-1: Non-roaming reference architecture for Location Services in reference point representation
NOTE 1: (R)AN represents NG-RAN, trusted non-3GPP access or untrusted non-3GPP access.
NOTE 2: Reference point interface related to charging functionality is not shown in this specification.
NOTE 3: PRU refers to a Positioning Reference Unit realized by a UE as defined in clause 5.4.5 of TS 38.305 [9].
Figure 4.2.1-2 shows an architectural reference model for 5GS LCS for a non-roaming UE and PRU in SBI representation.
Figure 4.2.1-2: Non-roaming reference architecture for Location Services in SBI representation
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4.2.2 Roaming reference architecture
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Figure 4.2.2-1 shows an architectural reference model for 5GS LCS for a roaming UE and PRU in reference point representation.
Figure 4.2.2-1: Roaming reference architecture for Location Services in reference point representation
NOTE 1: (R)AN represents NG-RAN, trusted non-3GPP access or untrusted non-3GPP access.
NOTE 2: Reference point interface related to charging functionality is not shown in this specification.
NOTE 3: PRU refers to a Positioning Reference Unit realized by a UE as defined in clause 5.4.5 of TS 38.305 [9].
Figure 4.2.2-2 shows an architectural reference model for 5GS LCS for a roaming UE and PRU in SBI representation.
Figure 4.2.2-2: Roaming reference architecture for Location Services in SBI representation
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4.2.3 Reference architecture with sidelink positioning
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Architectural reference model for 5GS LCS with sidelink positioning in reference point representation and in SBI representation is in clause 4.2 of TS 23.586 [40].
4.2a Interconnection between 5GC and EPC
4.2a.1 General
For MT-LR Location Request, when a LCS service request is received at 5GC GMLC, the target UE may be served by either 5GC or EPC. An EPC/5GC common interface is used between the LCS Client and the 5GC GMLC to enable the location service request being handled based on whether the target UE is served by EPC or 5GC. The AF initiates the service request to the 5GC GMLC via NEF.
NOTE: The LCS Client doesn't know if UE is currently served by EPC or 5GC.
For MT-LR Location Request, the 5GC interconnection with EPC happens:
- when an LCS service request is received by the 5GC GMLC and the target UE is served by EPC in non-roaming case;
- when an LCS request is received by the 5GC GMLC in the HPLMN of the target UE and the target UE is served by EPC in the VPLMN in roaming case.
4.2a.2 Non-roaming architecture
Figure 4.2a.2-1 represents the non-roaming architecture of Location Services for interconnection between 5GC and EPC.
Figure 4.2a.2-1: Non-roaming architecture of interconnection between 5GC and EPC
NOTE 1: EPC GMLC and 5GC GMLC can be collocated in implementation, in such case, Lr' is not needed.
NOTE 2: For this release, Lr' is not standardized.
NOTE 3: Interworking between 5GS and EPS is defined in clause 5.32.7 of TS 23.501 [18].
NOTE 4: The interaction between UDM and HSS, when they are deployed as separate network functions, is defined in TS 23.632 [42] and TS 29.563 [43] or it is implementation specific.
4.2a.3 Roaming architecture
Figure 4.2a.3-1 and Figure 4.2a.3-2 represent the Roaming architecture of interconnection between 5GC and EPC.
Figure 4.2a.3-1: Roaming architecture of Location Services for interconnection between 5GC and EPC (5GC GMLC and EPC GMLC are separately deployed in VPLMN)
Figure 4.2a.3-2: Roaming architecture of Location Services for interconnection between 5GC and EPC (5GC GMLC and EPC GMLC are co-located in VPLMN)
4.2b Positioning methods
The LCS feature utilises one or more positioning methods in order to determine the location of user equipment (UE). The positioning methods may use a trained ML Model available at the LMF.
Determining the position of a UE involves two main steps:
- Radio signal measurements or non-RAT measurements; and
- Position estimate computation based on the measurements.
The positioning methods for 3GPP access are described in clause 5.2.
The positioning methods for non-3GPP access are described in clause 5.3.1.
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4.3 Functional description of LCS per network function
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4.3.1 Access Network
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The Access Network is involved in the handling of various positioning procedures including positioning of a target UE, provision of location related information not associated with a particular target UE and transfer of positioning messages between an AMF or LMF and a target UE. The Access Network shall support determination of location estimates in geographical and/or local co-ordinates as defined in TS 23.032 [8].
In this version of the specification, location services are supported for NG-RAN and non-3GPP access.
The LCS specific functionalities of the radio access network elements are specified in TS 38.305 [9] for NG-RAN.
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4.3.2 LCS Clients, Application Functions and Network Functions
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AFs and NFs may access LCS services from a GMLC in the same trust domain (e.g. in the same PLMN) using the Ngmlc interface or Event Exposure with location information from an AMF in the same trust domain using the Namf interface. The NWDAF collects UE location information by accessing GMLC directly.
LCS Clients may access LCS services from a GMLC (e.g. HGMLC) using the Le reference point.
External AFs may access LCS services from an NEF using Nnef interface or CAPIF API. The CAPIF and associated API provider domain functions are specified in TS 23.222 [24].
An LCS Client or AF may access LCS services from a UE over a user plane connection for reporting of location events by the UE for a periodic or triggered 5GC-MT-LR when the UE is able to determine location estimates.
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4.3.3 Gateway Mobile Location Centre, GMLC
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The Gateway Mobile Location Centre (GMLC) contains functionality required to support LCS. In one PLMN, there may be more than one GMLC.
A GMLC is the first node an external LCS client accesses in a PLMN (i.e. the Le reference point is supported by the GMLC). AFs and NFs may access GMLC directly or via NEF. The GMLC may request routing information and/or target UE privacy information from the UDM via the Nudm interface. After performing authorization of an external LCS Client or AF and verifying target UE privacy, a GMLC forwards a location request to either a serving AMF using Namf interface or to a GMLC in another PLMN using the Ngmlc interface in the case of a roaming UE.
The target UE's privacy profile settings shall always be checked in the UE's home PLMN prior to delivering a location estimate.
The "Visited GMLC" (VGMLC) is the GMLC, which is associated with the serving node of the target UE.
The "Home GMLC" (HGMLC) is the GMLC residing in the target UE's home PLMN, which is responsible for the control of privacy checking of the target UE.
Additional functions which may be performed by a GMLC to support location services include the following:
- At an HGMLC, determine the serving AMF for a target UE when there is more than one serving AMF.
- At an HGMLC, determine whether to attempt a second location request for a target UE from a different AMF when location information returned by a first AMF does not meet QoS requirements and there is more than one serving AMF.
- At an HGMLC, support location requests from an external LCS client or NEF for a 5GC-MT-LR and deferred 5GC-MT-LR for periodic, triggered and UE available location events.
- At an HGMLC, support additional check of whether the UE is located within the requested target area for deferred 5GC-MT-LR for periodic, triggered and UE available location events.
- At an HGMLC, forward location requests for a roaming UE to a VGMLC or serving AMF in the VPLMN based on deployment configurations.
- At an HGMLC, receive event reports from a VGMLC or LMF for a deferred 5GC-MT-LR for periodic or triggered location and return to an external LCS Client or NEF.
- At an HGMLC, support cancelation of a periodic or triggered location.
- At an HGMLC, receive location information from an VGMLC for a 5GC-MO-LR and forwards to an LCS Client or an AF (via NEF) if requested by the UE.
- At a VGMLC, receive location requests from an HGMLC for a roaming UE and forward to a serving AMF.
- At a VGMLC, receive event reports from an LMF for a deferred 5GC-MT-LR for periodic or triggered location for a roaming UE and forward to an HGMLC.
- At a VGMLC, receive location information from an AMF for a 5GC-MO-LR and forwards to an HGMLC.
- At an HGMLC, reject the LCS request coming from a LCS client, e.g. when the number of Target UEs in the LCS request exceeds the Maximum Target UE Number of such client.
- At an HGMLC, allocate the reference number for each location request from an external LCS client for LDR.
- At an HGMLC, assign the pseudonym if pseudonym indicator is received in the service request and transfer it to external LCS client, e.g. when core network provides the UE's location information to LCS client. Resolve the verinym from the pseudonym, if it is received from the LCS client.
- At an HGMLC, resolve group identifier to identifier of individual UEs and aggregate responses to LCS Client or NEF during bulk operation procedure.
- At an HGMLC, verify a request for user plane reporting by an LCS Client or AF for a periodic or triggered 5GC-MT-LR and verify or assign parameters to the request to enable the target UE to establish a secure user plane connection to the LCS Client or AF. Subsequently, support the transfer of cumulative event reports from the target UE via control plane back to the LCS Client or AF.
- During UE mobility between 5GS and EPS, the GMLC transfers the LCS request between 5GS and EPS, may map the LCS QoS and (re-)initiate the LCS sessions towards the 5GS to/from EPS.
- At an HGMLC, determine a reporting indication on how a target UE sends event reports when the UE is outside the event report allowed area based on LCS privacy profile data, LCS Client type, the type of periodic or triggered location reporting and associated parameters.
- Support aggregation of a single UE's location estimates over a period of time for a periodic or triggered 5GC-MT-LR event.
- At an HGMLC or a VGMLC, for a regulatory location service, support multiple location reports if requested by the LCS client.
- At an HGMLC, transform the universal location co-ordinates provided by the AMF into some local geographic reference system.
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4.3.4 Location Retrieval Function, LRF
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The Location Retrieval Function (LRF) may be collocated with a GMLC or separate and is responsible for retrieving or validating location information, providing routing and/or correlation information for a UE which has initiated an IMS emergency session. The information is provided by an LRF to an E-CSCF. For more details, refer to TS 23.167 [10].
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4.3.5 UE
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A target UE may support positioning according to four different modes:
- UE assisted mode (the UE obtains location measurements and sends the measurements to another entity (e.g. an LMF) to compute a location);
- UE based mode (the UE obtains location measurements and computes a location estimate making use of assistance data provided by serving PLMN);
- standalone mode (the UE obtains location measurements and computes a location estimate without making use of assistance data provided by serving PLMN);
- network based mode (a serving PLMN obtains location measurements of signals transmitted by a target UE and computes a location estimate).
NOTE: The transmission of UE signals for network based mode may or may not be transparent to the UE.
Positioning procedures used by a UE for NG-RAN access are described in TS 38.305 [9].
A limited set of UE positioning capabilities and UE user plane positioning capabilities can be transferred to the 5GCN in the 5GMM capability during registration of the UE as described in TS 24.501 [11]. Some of these positioning capabilities may be transferred subsequently to an LMF as described in TS 29.572 [12]. UE positioning capabilities may also be transferred directly to a location server (e.g. LMF).
Additional functions which may be supported by a UE to support location services include the following.
- Support location requests received from a network for 5GC-MT-LR, 5GC-NI-LR or a deferred 5GC-MT-LR for periodic or triggered location.
- Support location requests to a network for a 5GC-MO-LR.
- Support privacy notification and verification for a 5GC-MT-LR or deferred 5GC-MT-LR for periodic or triggered location.
- Send updated privacy requirements to a serving AMF (for transfer to a UDR via UDM).
- Support periodic or triggered location reporting to an LMF.
- Support change of a serving LMF for periodic or triggered location reporting.
- Support cancelation of periodic or triggered location reporting.
- Support multiple simultaneous location sessions.
- Support the reception of unciphered and/or ciphered assistance data broadcast by NG-RAN.
- Support the reception of ciphering keys for the assistance data from the AMF.
- Support handling of 5GC-MT-LR, 5GC-NI-LR, 5GC-MO-LR and deferred 5GC-MT-LR for periodic or triggered location over a user plane connection between UE and LMF.
- Support reporting of location events for a periodic or triggered 5GC-MT-LR over a user plane connection to an LCS Client or AF with periodic cumulative event reports being sent over control plane to the LMF, H-GMLC and LCS Client or AF.
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4.3.6 UDM
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The UDM contains LCS subscriber LCS privacy profile and routing information. The UDM is accessible from an AMF, GMLC or NEF via the Nudm interface.
The UDM may also contain an indication whether a UE is allowed to serve as a PRU and indication whether PRU is stationary PRU as part of the UE subscription data.
The UDM may also contain LMF identifier(s) and indication of user plane positioning between UE and LMF in UE LCS subscription data.
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4.3.7 Access and Mobility Management Function, AMF
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The AMF contains functionality responsible for managing positioning for a target UE for all types of location request. The AMF is accessible to the GMLC and NEF via the Namf interface, to the RAN via the N2 reference point and to the UE via the N1 reference point.
Functions which may be performed by an AMF to support location services include the following.
- Initiate an NI-LR location request for a UE with an IMS emergency call or to know a UE geographical area with NR satellite access for PLMN selection verification.
- Receive and manage location requests from a GMLC for a 5GC-MT-LR and deferred 5GC-MT-LR for periodic, triggered and UE available location events.
- Receive and manage location requests from a UE for a 5GC-MO-LR.
- Receive and manage Event Exposure request for location information from an NEF.
- Select an LMF.
- Receive updated privacy requirements from a UE and transfer to a UDR via UDM.
- Support cancelation of periodic or triggered location reporting for a target UE.
- Support cancelation of a 5GC-MT-LR or 5GC-MO-LR during UE mobility from 5GS to EPS with N26 interface.
- Support change of a serving LMF for periodic or triggered location reporting for a target UE.
- When assistance data is broadcast by 5GS in ciphered form, the AMF receives ciphering keys from the LMF and forwards to suitably subscribed UEs using mobility management procedures.
- Store UE Positioning Capability received from an LMF and send the UE Positioning Capability along with the received location request to an LMF.
- Receive and store UE user plane positioning capabilities (the user plane positioning using LCS-UPP and/or the user plane positioning using SUPL [49]) as part of the "5GMM capability" from UE.
- Receive UL NAS Transport including a PRU Association, Association Update, or Disassociation Request (contained in an LCS supplementary service message) from a UE.
- AMF may verify whether a UE can serve as a PRU based on UE subscription data after receiving the PRU Association Request, Association Update, or Disassociation. AMF may also use local policy to determine if UEs are allowed to serve as a PRU. AMF may verify based on subscription information or local policy if PRU can work as stationary PRU.
- Sends the PRU Association Request or PRU Disassociation Request to LMF and may include a UE verification indication indicating whether this UE is authorized to serve as a PRU.
- Support verifying whether UE is subscribed with user plane positioning between UE and LMF and triggering LMF to establish a User Plane Connection to UE if UE requested that.
- Support subscribing from LMF status of LCS user plane connection between a UE and the LMF.
- Store in UE context that UE has a maintained User Plane connection with certain LMFs.
NOTE: Details of UE Positioning Capability is defined in TS 37.355 [20].
- Support of local configuration of a mapping table of UE identifier ranges and LMF identifier(s) or querying the UDM the LMF identifier for a UE for a 5GC-MO-LR.
- Support the 5G to EPS Handover by providing the target MME ID to GMLC as part of the LCS Service response.
- Support interaction with NWDAF to obtain UE related analytics to assist with UE location verification for NR satellite access.
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4.3.8 Location Management Function, LMF
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The LMF manages the overall co-ordination and scheduling of resources required for the location of a UE that is registered with or accessing 5GCN. It also calculates or verifies a final location and any velocity estimate and may estimate the achieved accuracy. The LMF receives location requests for a target UE from the serving AMF using the Nlmf interface. The LMF interacts with the UE in order to exchange location information applicable to UE assisted and UE based position methods, interacts with the NG-RAN, N3IWF or TNAN in order to obtain location information and optionally interacts with NWDAF to retrieve ML model(s).
The LMF shall determine the result of the positioning in geographical co-ordinates as defined in TS 23.032 [8] and/or in local co-ordinates as defined in TS 23.032 [8]. If requested and if available, the positioning result may also include the velocity of the UE. The coordinate type(s) is determined by LMF when receiving a location request, based on LCS Client type and supported GAD shapes. If the location request indicates regulatory LCS Client type the LMF shall determine a geographical location and optionally a location in local coordinates. For location request indicates a value added LCS Client type, the LMF may determine the UE location in local coordinates or geographical co-ordinates or both. If the supported GAD shapes is not received or Local Co-ordinates is not included in the supported GAD shapes, the LMF shall determine a geographical location.
NOTE 1: Some RAT independent position methods (e.g. GNSS based position methods) can only determine a UE location in geographical co-ordinates. In such a case, the LMF may translate a UE location in geographical co-ordinates into a location in local co-ordinates when an origin for the local co-ordinates has known global coordinates. When an origin for the local co-ordinates does not have known global coordinates, position methods that can only determine a UE location in geographical co-ordinates cannot be used to determine a UE location in local co-ordinates.
Additional functions which may be performed by an LMF to support location services include the following.
- Support a request for a single location received from a serving AMF for a target UE.
- Support a request for periodic or triggered location received from a serving AMF for a target UE.
- Determine type and number of position methods and procedures based on UE and PLMN capabilities, QoS, UE connectivity state per access type, LCS Client type, co-ordinate type and optionally service type and indication of requiring reliable UE location information. If the indication of requiring reliable UE location information is received, the LMF selects positioning method as per the TS 33.256 [51].
- Report UE location estimates directly to a GMLC for periodic or triggered location of a target UE.
- Support cancelation of periodic or triggered location for a target UE.
- Support cancelation of a 5GC-MT-LR or 5GC-MO-LR during UE mobility from 5GS to EPS with N26 interface.
- Support the provision of broadcast assistance data to UEs via NG-RAN in ciphered or unciphered form and forward any ciphering keys to subscribed UEs via the AMF.
- Support change of a serving LMF for periodic or triggered location reporting for a target UE.
- Support of receiving stored UE Positioning Capability from AMF and support of providing updated UE Positioning Capability to AMF.
- Map the UE location to a geographical area where the PLMN is or is not allowed to operate based on the request from AMF.
- Support determination of a UE location at a scheduled location time.
- Support determination of indoor or outdoor for a location estimate.
- Determine whether to use user plane or control plane for positioning.
- Support handling of 5GC-MT-LR, 5GC-NI-LR, 5GC-MO-LR and deferred 5GC-MT-LR for periodic or triggered location over a user plane connection between UE and LMF over TLS.
NOTE 2: How the LMF uses the received UE user plane positioning capability for SUPL [49] is left to the implementation.
- Support requesting ML model provision from NWDAF containing MTLF for LMF-based AI/ML Positioning.
Editor's note: Whether LMF can retrieve ML model from OAM needs confirmation from SA WG5.
- Determine whether to use an ML Model for UE positioning. Trigger data collection for training of the ML Model and for monitoring of the performance of the ML Model. The LMF retrieves user consent for data collection for the purpose of ML model training from UDM as defined in TS 23.502 [19].
- Support training ML model locally using the training data collected from UE and/or gNB.
- Monitoring the performance of the ML model used for UE positioning.
- Support collection of GNSS assistance data from AFs.
- Support service level PRU Association, PRU Association update or PRU Disassociation.
- LMF supports verification of a PRU initiated Association or Disassociation by checking whether there is an PRU verified indication from AMF.
- LMF stores the received PRU information contained in service level PRU Association message and removes the PRU information after PRU Disassociation.
- LMF keeps PRU information for PRUs which are in OFF state.
- LMF may indicate support of PRU function to NRF via NF profile and may further send the PRU indication via NF profile update if PRU is stationary PRU.
- LMF may request a PRU to associate to a new LMF by returning a Routing ID of the new LMF.
PRU ON/OFF states indicate temporarily availability of the PRU functionality of a UE at the serving LMF (e.g. PRU OFF due to other high priority tasks/energy saving at the UE, or the UE temporarily loses network coverage).
- Support selection of a PRU based on stored PRU information if the LMF needs to obtain the location measurements from the PRU to assist positioning of a target UE.
- If the LMF determines to use UE based positioning and to use PRU to improve the positioning result, it supports to provide the assistance data including location measurements from the PRU, the associated timestamp and the PRU location to the target UE which is responsible to calculate location based on the assistance data.
- Support to obtain PRU location measurements as described in clause 5.4.5 of TS 38.305 [9] by triggering the procedure in clause 6.11.
- Support to obtain PRU location measurements from other PRU serving LMF(s).
- As a serving LMF of target UE(s), support discovery and selection of other PRU serving LMF(s) by querying the NRF and support to request PRU location measurements from the selected LMF(s).
- As a serving LMF of PRU(s), support to provide PRU location measurements to other LMF(s) after receiving a request from other LMF(s).
- Support to determine UE location by considering obtained PRU location measurements.
- Support to determine UE location by considering target UE location measurements and PRU location measurements in the time window(s). In the case that the serving LMF of target UE and the serving LMF of PRU are different LMFs:
- If network assisted positioning is used by the serving LMF of target UE, it provides the positioning method, time window(s) and the identifier of TRPs for the measurements to the serving LMF of PRU. The serving LMF of PRU triggers network assisted positioning based on the received information and returns the PRU location measurements to the serving LMF of target UE.
- If UE assisted positioning is used by the serving LMF of target UE, it provides the positioning method and time window(s) to the serving LMF of PRU. The serving LMF of PRU triggers UE assisted positioning based on the received information and returns the PRU location measurements to the serving LMF of target UE.
NOTE 3: Country, area within a country, or an international area can be supported as different types of geographical area.
- Support a request for user plane reporting from a UE to an LCS Client or AF for a periodic or triggered 5GC-MT-LR. Subsequently, support the transfer of cumulative event reports from the target UE via control plane back to the H-GMLC and LCS Client or AF. Also support any request for assistance data received in a cumulative event report.
- Determine UE location for a UE connecting to a MBSR or MWAB based on location and velocity of the MBSR or MWAB and the timing of the location estimations for the target UE and MBSR or MWAB.
- For a regulatory location service, support reporting of multiple INTERMEDIATE location estimates to GMLC.
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4.3.9 Network Exposure Function, NEF
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An NEF provides a means of accessing location services by an external AF or internal AF. AFs access location services from an NEF using an API. Depending on QoS requirements, an NEF can forward a location request to a GMLC or request an event exposure for location information from serving AMF (optionally via a UDM). When event exposure via AMF is used, an NEF may request routing information and/or target UE privacy information from the UDM via the Nudm interface.
Additional functions which may be performed by an NEF to support location services include the following.
- Support location requests from an AF for immediate location and for deferred periodic and triggered location events.
- Support location information exposure to an AF based on the location request.
- Support determination of GMLC or AMF based on e.g. the QoS requirements from AF, type of the location request.
NOTE: If the GMLC or AMF are determined based on the QoS requirements and the QoS requirements include Multiple QoS class, the determination of GMLC or AMF is done based on the most stringent (i.e. primary) QoS requirements.
- Select the serving AMF for a target UE when there is more than one serving AMF.
- Determine whether to attempt a second location request for a target UE from a different AMF when location information returned by a first AMF does not meet QoS requirements and there is more than one serving AMF.
- Support UE LCS privacy profile provision from the AF.
- Support suspending and cancellation of a periodic or triggered location request.
- Support authorization of LCS request from the AF.
- Support rejecting the LCS request coming from an AF, e.g. when the number of Target UEs in the LCS request exceeds the Maximum Target UE Number of such client.
- Support allocating the reference number for each location request from an AF for LDR.
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4.3.10 Unified Data Repository, UDR
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The UDR contains privacy data information for target UEs and may be updated by a serving AMF via UDM with new privacy information received from a UE.
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4.3.11 Positioning Reference Unit, PRU
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A UE may support the functions of a PRU. The PRU supports the following functions including functions defined in TS 38.305 [9]:
- Support service level association, association update and disassociation with a serving LMF.
- The PRU sends service level association, association update or disassociation to LMF via LCS supplementary service message.
- Support association with multiple LMFs. e.g. for the case a PRU is in multiple LMF overlapped serving areas.
- The PRU information included in a PRU association or PRU association update contains one or more than one of the following aspects:
- PRU Positioning Capabilities.
- Location information if known.
- PRU ON/OFF state.
PRU ON/OFF states indicate temporarily availability of the PRU functionality of a UE at the serving LMF.
A UE accesses 5G network via NR satellite shall not operate as a PRU.
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4.3.12 Network Repository Function, NRF
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In addition to the functions defined in TS 23.501 [18], the NRF may perform the following functions:
- Support to store or update PRU existence indication in TAI level in LMF profile based on request from PRU serving LMF.
- Support LMF(s) with PRU function discovery by AMF.
- LMF discovery by considering user plane Positioning Capability.
- Support LMF(s) associated with PRUs discovery by other LMF(s), according to target area in the discovery request and the LMF profiles with PRU existence indication in TAI level.
- LMF discovery by considering the support of LCS when MBSR is involved.
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4.3.13 Network Data Analytics Function, NWDAF
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LMF may provide input data to NWDAF for ML model training or ML model performance monitoring for LMF-based AI/ML Positioning.
LMF may obtain ML model from NWDAF for performing AI/ML Positioning.
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4.4 Reference Point to Support Location Services
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4.4.1 Le Reference Point
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The Le reference point supports location requests sent by an LCS Client to a GMLC or LRF.
The Le reference point may be supported using the Mobile Location Protocol (MLP) defined by OMA [13].
The Le reference point may also be supported using the HTTP-Enabled Location Delivery (HELD) [52] in location session associated with emergency services.
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4.4.2 NL3 Reference Point
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The NL3 reference point supports location requests forwarded by an HGMLC to a VGMLC.
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4.4.3 N1 Reference Point
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The N1 reference point supports transfer of supplementary services messages between a serving AMF and target UE to support privacy notification and verification and change of UE privacy preference. The N1 reference point also supports transfer of positioning protocol messages and location event reports between a target UE and an LMF via a serving AMF. The N1 reference point supports the transfer of ciphering keys from an AMF to a suitably subscribed UE to enable the UE to receive ciphered broadcast assistance data. All messages sent over the N1 reference point for support of location services are encapsulated in NAS Transport messages as defined in TS 24.501 [11].
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4.4.4 N2 Reference Point
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The N2 reference point supports transfer of positioning messages, via an AMF, between an LMF and a RAN node, or N3IWF in the case of untrusted non-3GPP access. The N2 reference point also supports transfer of messages, via an AMF, from an LMF to an NG-RAN node, which carry assistance data to be broadcast by the NG-RAN node. Positioning messages relevant to the N2 interface are defined in TS 38.455 [15].
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4.4.5 Void
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4.4.6 NL5 Reference Point
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The NL5 reference point supports location requests sent by an NEF or other NF to a GMLC.
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4.4.7 NL2 Reference Point
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The NL2 reference point supports location requests sent by a GMLC to a serving AMF for a target UE.
Messages for the NL2 reference point are defined in TS 29.518 [16].
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4.4.8 NL6 Reference Point
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The NL6 reference point supports queries from an HGMLC to a UDM for privacy subscription information for a target UE and routing information for a target UE.
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4.4.9 N51 Reference Point
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The N51 reference point supports queries from an NEF to a serving AMF for the location of a target UE.
Messages for the N51 reference point are defined in TS 29.518 [16].
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4.4.10 NL1 Reference Point
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The NL1 reference point supports location requests for a target UE sent from a serving AMF for the target UE to an LMF. Location requests are supported for immediate location and for deferred location for periodic or triggered location events.
The NL1 reference point also supports the transfer from an LMF to an AMF of ciphering keys and associated data that enable deciphering by suitably subscribed UEs of ciphered broadcast assistance data.
Messages for the NLI reference point are defined in in TS 29.518 [16] and TS 29.572 [12].
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4.4.11 N52 Reference Point
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The N52 reference point supports queries from an NEF to a UDM for privacy subscription information for a target UE and routing information for a target UE. The N52 interface also supports a request from an NEF to a UDM to forward a location request from the NEF to a serving AMF for the target UE.
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4.4.12 NL7 Reference Point
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The NL7 reference point supports location context transfer between two LMFs.
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4.4.13 NL8 Reference Point
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The NL8 reference point supports LMF to receive location related analytics from NWDAF, provide input data for model training or model performance monitoring to NWDAF, or receive AI/ML positioning model from NWDAF, as defined in TS 23.288 [37].
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4.4.14 NL9 Reference Point
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The NL9 reference point supports location requests sent by NWDAF to a GMLC.
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4.4.15 NL10 Reference Point
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The NL10 reference point supports LMF to send location requests to GMLC in case of 5GC-MT-LR involving MBSR and MWAB. Additionally, this reference point is used by LMF to send location result directly to GMLC in case of Deferred Location or 5GC-MT-LR multiple location or in case of support for PNI-NPN architecture.
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4.4.16 NL11 Reference Point
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NL11 reference point enables user plane between UE and LMF.
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4.5 Service Based Interfaces to Support Location Services
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The 5GS LCS architecture contains the following service-based interfaces for Location Services:
Nlmf: Service-based interface exhibited by LMF.
Ngmlc: Service-based interface exhibited by GMLC.
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5 High Level Features
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5.1 LMF Discovery and Selection
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LMF selection functionality is supported by the AMF to determine an LMF for location estimation of the target UE or Ranging/Sidelink Positioning between Target UE and SL Reference UE. The LMF selection functionality is also supported by the LMF if it determines that it is unsuitable or unable to support location for the current UE access network or serving cell for the deferred 5GC-MT-LR procedure for periodic, triggered location events, or Modification of User Plane Connection. The LMF selection functionality may also be supported by the GMLC and the GMLC provides the selected LMF ID to AMF.
LMF reselection is a functionality supported by AMF when necessary, e.g. due to UE mobility.
The LMF selection/reselection may be performed at the AMF or LMF or GMLC based on the locally available information i.e. LMF profiles are configured locally at AMF or LMF or GMLC, or by querying NRF.
The following factors may be considered during the LMF selection:
- LCS client type.
- Requested Quality of Service information, e.g.:
- LCS accuracy,
- Response time (latency),
- Access Type (3GPP /N3GPP).
NOTE 1: Location methods may differ depending on the Access Type, e.g. in the case of WLAN Access Location determination may just correspond to retrieval of IP addressing information from the N3IWF/TNGF; As another example, for Wireline access, Location determination may just correspond to retrieval of geo coordinates corresponding to a GLI as defined in clause 4.7.8 of TS 23.316 [21] or a HFC Node ID.
- RAT type (e.g. 5G NR, eLTE, or any of the RAT Types specified for NR satellite access) and/or the serving AN node (i.e. gNB or NG-eNB) of the target UE.
- RAN configuration information.
- LMF capabilities, including:
- the support of Uu based positioning as defined in clause 4.3.8;
- Ranging/Sidelink positioning as defined in clause 4.3.8 of TS 23.586 [40];
- LMF user plane positioning capabilities (the capability to support LCS-UPP);
- AI/ML positioning capability.
NOTE 2: The AI/ML positioning capability is used by LMF for LMF re-selection only.
- LMF load.
- LMF location.
- Indication of either a single event report or multiple event reports.
- Duration of event reporting.
- Network slicing information, e.g. S-NSSAI and/or NSI ID.
- LMF Service Area consisting of one or more TA(s).
- Supported GAD shapes.
- Support LCS when MBSR is involved.
- Support LCS when MWAB is involved.
- Requested UE has maintained user plane connection with certain LMFs.
When receiving a NAS message from UE, including an LMF ID together with a LPP message (refer to step 25 in clause 6.3.1 for event reporting for a deferred 5GC-MT-LR), AMF sends the LPP message to the LMF, as indicated by the LMF ID.
NOTE 3: Description on how UE encapsulates the LMF ID in the NAS message is documented in TS 24.571 [36].
UDM may store the LMF ID in UE subscription data. During the location procedure, GMLC received the LMF ID from the UDM and provides it to AMF.
GMLC may be configured with the following parameters:
- LMF ID and/or
- per group ID and its correlating LMF ID.
The AMF may use locally provisioned configuration to determine LMF based on UE identify or its group information.
NOTE 4: It is AMF implementation specific for the priority of different selection criteria from GMLC, AMF and LMF.
When the GMLC receives a MT location request from LCS client/AF, GMLC determines the LMF ID based on the configured parameters for an LCS Client/AF. In case a group ID is provided or derived from the location request, GMLC determines the correlating LMF ID based on the provisioned group ID.
GMLC may have configuration with one or several dedicated LMF ID(s), irrelevant to any LCS client/AF. When the GMLC receives a MT location request from LCS client/AF, GMLC only determines the LMF ID within the configuration for all LCS client/AF.
NOTE 5: When AMF can't access the LMF instance of the LMF ID, by default, AMF replies to corresponding error to GMLC. GMLC could retry or fail the request accordingly; with explicit configuration to serve as backup selection in this, AMF can also select different configured LMF instance.
5.1a GMLC Discovery and Selection
More than one GMLC in the HPLMN can serve the location requests for a single UE. GMLC discovery and selection functionality is supported by AMF, LMF, NEF, LCS client and GMLC.
A LCS client may be configured with GMLC address(es). It may also determine the GMLC address by performing a DNS query.
A NEF, LMF, AMF or GMLC may be configured with GMLC address(es). Those NF may also query the NRF to get GMLC address(es).
In the following scenarios, information about the GMLC instance may be provided by UE, in such case, this GMLC instance is used:
- In the deferred MT-LR procedure, when UE reports the detected event to the AMF, it may also include the (H)GMLC address.
- In the MO-LR procedure, when UE initiates the LCS service request, it may also include the (H)GMLC address if the location estimation is reported to the (H)GMLC.
AMF may be configured locally a mapping table of UE identity e.g. MSISDN and GMLC address. When receiving a MO-LR, AMF determines GMLC based on local configuration.
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5.2 3GPP access specific aspects
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When 3GPP access type is selected, the positioning methods for 3GPP access defined in TS 38.305 [9] apply.
Access Type Selection for LCS Service is defined in clause 5.3.2.
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5.3 Non-3GPP Access Specific Aspects
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5.3.1 Location Information for Non-3GPP Access
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If the UE registered to non-3GPP access, following information can be regarded as UE location information:
Table 5.3.1-1: Supported UE location information of non-3GPP access
Untrusted non-3GPP Access
Trusted non-3GPP Access
Wireline Access
UE Side
N5CW device Side for Trusted WLAN Access
5G-RG side for Wireline Access
UE local IP address,
In the case of WLAN access, BSSID of the attached AP or BSSID of detected AP,
Civic address and/or geospatial location information (NOTE 1, NOTE 5, NOTE 6).
UE/N5CW device local IP address (NOTE 2).
In the case of WLAN access, BSSID of the attached AP or BSSID of detected AP,
Civic address and/or geospatial location information (NOTE 1, NOTE 5, NOTE 6).
Null
N3IWF Side for Untrusted non-3GPP Access;
TNGF Side for trusted non-3GPP Access;
TWIF Side for trusted WLAN Access;
W-AGF Side for wireline Access
UE local IP address and optionally UDP or TCP source port (NOTE 2)
UE/N5CW device local IP address and optionally UDP or TCP source port (NOTE 2),
TNAP/TWAP Id (NOTE 2)
HFC node ID for 5G-CRG in clause 10.1 of TS 23.316 [21];
GLI for 5G-BRG in clause 10.1 of TS 23.316 [21].
AMF Side
UE local IP address and optionally UDP or TCP source port (NOTE 3).
Last known 3GPP access User Location Info (NOTE 4).
UE/N5CW device local IP address and optionally UDP or TCP source port (NOTE 2, NOTE 3).
Last known 3GPP access User Location Info (NOTE 4).
TNAP/TWAP Id (NOTE 2)
HFC node ID for 5G-CRG in clause 10.1 of TS 23.316 [21];
GLI for 5G-BRG in clause 10.1 of TS 23.316 [21]
NOTE 1: In the case of WLAN access, the UE may retrieve its location from a WLAN AP, prior or after association with the AP, requesting the Civic Location ANQP element, the Geospatial Location ANQP element or both as specified in IEEE Std 802.11-2012, using ANQP procedures described in HS2.0 Rel-12 specification.
NOTE 2: More details can refer to clause 5.6.2 of TS 23.501 [18].
NOTE 3: This location information can be provided by location change event, more details can refer to clause 5.2.2.3.1 of TS 23.502 [19].
NOTE 4: This location information is also named as Last known Cell-Id, more details can refer to clause 5.6.2 of TS 23.501 [18].
NOTE 5: Geospatial location information can be obtained if UE (e.g. laptop) has installed GNSS receiver, i.e. GPS.
NOTE 6: Some Applications (e.g. Google Map) may map the WiFi AP's BSSID with the geospatial locations obtain through GPS when the UE switch on the GPS and WiFi simultaneously. When another UE detect the same AP, the Application will send the geospatial locations to the UE. Thus the UE obtain the geospatial locations even without switch on the GPS. If the Application map the geospatial locations to civic address, the UE can also obtain the civic address.
If the UE registered to 3GPP access and non-3GPP access simultaneously, following information can be regarded as UE location information:
- All location information when the UE only registered to non-3GPP access,
- All location information when the UE only registered to 3GPP access, more details can refer to TS 36.305 [7].
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5.3.2 Access Type Selection for LCS Service
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The positioning of a UE can be performed via either 3GPP access network or non-3GPP access network.
For a MT-LR Location Service request, in order to select the positioning access type, the GMLC uses information retrieved from the UDM and optionally serving AMFs, e.g. access type, its serving AMF identity(ies), and UE connectivity state of this access, if available, and locally configured operator policy as follows:
- If only one AMF identity is provided by the UDM, the GMLC selects this AMF for UE positioning.
- When the UE is concurrently served by multiple PLMNs respectively for 3GPP access and non-3GPP access, multiple AMF identities with corresponding access types may be provided by the UDM, and the GMLC selects one access type and its associated AMF, which may be based on access type and its AMF, UE connectivity state per access type information, if this is retrieved from UDM or AMFs, PLMN identity, and/or locally configured operator policy. If the location estimation result provided by this AMF cannot fulfil the QoS requirements, the GMLC may reselect another access type and its associated AMF from the candidate list provided by the UDM to perform positioning.
When AMF receives a MT-LR Location Service request, the AMF shall provide to the LMF UE connectivity state per access type as well as the QoS requirement that are received from the GMLC.
When AMF receives the event report from the UE for a periodic or triggered MT-LR Location Service, the AMF may select a LMF or use the LMF indicated by the UE as described in clause 6.4 and clause 6.3.1 and may provide the UE connectivity state per access type to the LMF.
The LMF determines the positioning access type and positioning method based on the QoS requirement, UE/network positioning capability, and UE connectivity state per access type received from the AMF and the locally configured operator policy.
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5.4 UE LCS privacy
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5.4.1 General
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An LCS client or AF may or may not be authorised to retrieve the UE location, e.g. for commercial use. UE LCS privacy is a feature which allows a UE and/or AF to control which LCS clients and AFs are and are not allowed access to UE location information. UE LCS privacy can be supported via subscription and via UE LCS privacy profile handling.
With subscription, privacy preferences for a UE are stored in a UE LCS privacy profile as part of UE subscription data in the UDM and queried from the UDM by another NF such as GMLC or NEF. The UDM may also store the UE privacy profile in the UDR. In this release of the specification, subscription of privacy preferences is restricted to the Call/Session unrelated Class as defined in clause 5.4.2.2.3 and the PLMN Operator Class as defined in clause 5.4.2.2.4.
With UE LCS privacy profile handling, the UE and/or AF can provide and update part of the UE privacy profile and provide it to the network as an update to the UDR. In this release of the specification, UE LCS privacy profile handling is restricted to the Location Privacy Indication as defined in clause 5.4.2.3.
The UE LCS privacy profile is used to indicate whether LCS requests from LCS clients and AFs are allowed or disallowed, together with the POI as defined in clause 5.4.4.
NOTE: In clause 5.4, even if the UE LCS privacy detail is only described for LCS client, the same detail is also applicable for AF, if no exception statement.
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5.4.2 Content of UE LCS Privacy Profile
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