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4.3.5.6 Idle mode signalling reduction function
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The Idle mode Signalling Reduction (ISR) function provides a mechanism to limit signalling during inter-RAT cell-reselection in idle mode (ECM-IDLE, PMM-IDLE, GPRS STANDBY states).
NOTE 1: The Idle mode Signalling Reduction function is mandatory for E-UTRAN UEs that support GERAN and/or UTRAN and optional for core network. The UE's ISR capability in the UE Core Network Capability element is for test purpose.
The MME/SGSN activates ISR only if the Serving GW supports the ISR. How MME/SGSN determines a Serving GW supports ISR is implementation dependent.
ISR shall be activated by decision of the CN nodes and shall be explicitly signalled to the UE as "ISR activated" in the RAU and TAU Accept messages. The UE may have valid MM parameters both from MME and from SGSN. The "Temporary Identity used in Next update" (TIN) is a parameter of the UE's MM context, which identifies the UE identity that the UE shall indicate in the next RAU Request, TAU Request or Attach Request message. The TIN also identifies the status of ISR activation in the UE.
The TIN can take one of the three values, "P‑TMSI", "GUTI" or "RAT-related TMSI". The UE shall set the TIN when receiving an Attach Accept, a TAU Accept or RAU Accept message according to the rules in table 4.3.5.6-1.
Table 4.3.5.6-1: Setting of the TIN
Message received by UE
Current TIN value stored by UE
TIN value to be set by the UE when receiving message
Attach Accept via E-UTRAN
(never indicates "ISR Activated")
Any value
GUTI
Attach Accept via GERAN/UTRAN
(never indicates "ISR Activated")
Any value
P-TMSI
TAU Accept
not indicating "ISR Activated"
Any value
GUTI
TAU Accept
indicating "ISR Activated"
GUTI
P‑TMSI or RAT-related TMSI
GUTI
RAT-related TMSI
RAU Accept
not indicating "ISR Activated"
Any value
P‑TMSI
RAU Accept
indicating "ISR Activated"
P‑TMSI
GUTI or RAT-related TMSI
P‑TMSI
RAT-related TMSI
When "ISR Activated" is indicated by the RAU/TAU Accept message but the UE shall not set the TIN to "RAT-related TMSI" is a special situation. Here the UE has deactivated ISR due to special situation handling. By maintaining the old TIN value the UE remembers to use the RAT specific TMSI indicated by the TIN when updating with the CN node of the other RAT.
Only if the TIN is set to "RAT-related TMSI" ISR behaviour is enabled for the UE, i.e. the UE can change between all registered areas and RATs without any update signalling and it listens for paging on the RAT it is camped on. If the TIN is set to "RAT-related TMSI", the UE's P‑TMSI and RAI as well as its GUTI and TAI(s) shall remain registered with the network and shall remain valid in the UE.
Table 4.3.5.6-2: Temporary UE Identity that the UE shall indicate in Attach Request and TAU/RAU Request (as "old GUTI" or as "old P‑TMSI/RAI" information element)
Message to be sent by UE
TIN value: P-TMSI
TIN value: GUTI
TIN value: RAT-related TMSI
TAU Request
GUTI mapped from P‑TMSI/RAI
GUTI
GUTI
RAU Request
P-TMSI/RAI
P‑TMSI/RAI mapped from GUTI
P‑TMSI/RAI
Attach Request via E-UTRAN
GUTI mapped from P‑TMSI/RAI
GUTI
GUTI
Attach Request via GERAN/UTRAN
P‑TMSI/RAI
P‑TMSI/RAI mapped from GUTI
P‑TMSI/RAI
Table 4.3.5.6-2 shows which temporary identity the UE shall indicate in a Tracking or Routing Area Update Request or in an Attach Request message, when the UE stores these as valid parameters.
Situations may occur that cause unsynchronized state information in the UE, MME and SGSN. Such special situations trigger a deactivation of ISR locally in the UE.
The UE shall deactivate ISR locally by setting its TIN to the temporary identity of the currently used RAT in following special situations:
- Modification of any EPS bearer context or PDP context which was activated before the ISR is activated in the UE;
- At the time when the UE moves from E‑UTRAN to GERAN/UTRAN or moves from GERAN/UTRAN to E‑UTRAN by means other than PSHO, if any EPS bearer context or PDP context activated after the ISR was activated in the UE exists;
- At the time when the UE moves from GERAN/UTRAN to E‑UTRAN by means other than PSHO and CS to PS SRVCC, if the PDP contexts were suspended in GERAN and not successfully resumed before returning to E‑UTRAN;
- After updating either MME or SGSN about the change of the UE specific DRX parameters to guarantee that the other CN node is also updated;
- After updating either MME or SGSN about the change of the UE Core Network Capabilities to guarantee that the other CN node is also updated;
- E-UTRAN selection by a UTRAN-connected UE (e.g. when in URA_PCH to release Iu on UTRAN side);
- E-UTRAN selection from GERAN READY state;
- GERAN selection by an E-UTRAN-connected UE via Cell Change Order that is not for CS fallback;
- After a LAU procedure if the UE has CS fallback and/or SMS over SGs activated.
- For a UE that is IMS registered for voice, then after that UE moves from a Tracking Area List that supports IMS voice over PS sessions (see 4.3.5.8 for more information) to one that does not, and vice versa. It shall be possible, e.g. using Device Management or initial provisioning, to configure the UE to apply/not apply this particular exception.
NOTE 2: A UE moving between Tracking Area Lists that both support IMS voice over PS sessions, or that both do not support IMS voice over PS sessions, is unaffected by the above.
The UE shall deactivate ISR locally by setting its TIN to the temporary identity of the RAT that is still available to the UE in following special situations:
- After the RAT-specific Deactivate ISR timer expires, e.g. because the coverage of that RAT is lost or the RAT is no more selected by the UE (this may result also in implicit detach by SGSN or MME).
ISR shall be deactivated in the UE by the CN node using normal update signalling, i.e. by omitting the signalling of "ISR Activated", in following special situations:
- CN node change resulting in context transfer between the same type of CN nodes (SGSN to SGSN or MME to MME);
- Serving GW change;
- When the UE only has bearers related to emergency bearer service;
- When the UE is registered for RLOS service;
- TAU or RAU when UE moves over the border between local and macro network where SIPTO at local network with stand-alone GW and Serving GW relocation without mobility are supported in the core network.
- TAU or RAU when the network confirms to use PSM for the UE.
If tracking area list or routing area covers both local network and macro network, the ISR shall not be activated if the UE is allowed to use SIPTO at local network and Serving GW relocation without mobility are supported in the core network.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.5.7 Mobility Restrictions
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Mobility Restrictions comprises the functions for restrictions to mobility handling of a UE in E-UTRAN access. The Mobility Restriction functionality is provided by the UE, the radio access network and the core network.
Mobility Restriction functionality in state ECM-IDLE is executed in UE based on information received from the core network. Mobility Restriction functionality in state ECM-CONNECTED is executed in the radio network and the core network.
In state ECM-CONNECTED, the core network provides the radio network with a Handover Restriction List. The Handover Restriction List specifies roaming, area and access restrictions. If roaming restriction to GERAN or UTRAN access needs to be enforced, a MME that is connected to eNodeBs that may handover or invoke release with redirection to UTRAN or GERAN is configured with a list of HPLMN IDs that are permitted to access GERAN or UTRAN unless restricted by the UE individual access restriction information received from HSS.
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495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.5.8 IMS voice over PS Session Supported Indication
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The serving PLMN shall send an indication toward the UE during the Attach procedure and Tracking Area Update procedures if an IMS voice over PS session is supported. The serving PLMN uses this indicator to indicate to the UE whether it can expect a successful IMS voice over PS session according to TS 22.173 [73] with a bearer that supports Conversational Voice as specified in TS 23.203 [6]. A UE with "IMS voice over PS" voice capability should take this indication into account when establishing voice over PS sessions (as specified in TS 23.221 [27]) as well as when determining whether to deactivate the special handling of ISR locally (as detailed in clause 4.3.5.6).
The serving PLMN provides this indication based e.g. on local policy, HPLMN, Voice Support Match Indicator, the SRVCC capability of the network and UE and/or extends of E-UTRAN/UTRAN coverage. The serving PLMN shall indicate to the UE that the UE can expect a successful IMS voice over PS session only if the MME is configured to know that the serving PLMN has a roaming agreement for IMS voice with the HPLMN of the UE. This indication is per TAI list.
On request by the HSS, the MME shall indicate the following:
- whether or not an IMS voice over PS Session is supported in the TA(s) that are registered for the UE ("IMS voice over PS Session Supported Indication"), together with the time of the last radio contact with the UE; and
- the current RAT type.
NOTE: In order to support routing of incoming IMS voice calls to the correct domain (PS or CS), the network-based T-ADS (see TS 23.292 [60] and TS 23.221 [27]) requires that there is homogeneous support/non-support of IMS voice over PS session for all registered TAs of the UE.
4.3.5.8A Homogenous Support of IMS Voice over PS Sessions Indication
The "Homogenous Support of IMS Voice over PS Sessions" indication is provided by the MME to the HSS, and can be used by the HSS to avoid requesting the serving nodes whether or not an IMS Voice over PS session according to TS 22.173 [73] with a bearer that supports Conversational Voice as specified in TS 23.203 [6] is supported. This indication is stored in the MME MM context.
The MME shall behave as follows whenever it sends a Update Location Request or a Notify Request message to the HSS:
- if "IMS Voice over PS Sessions" is supported homogeneously in all TAs in the serving MME for the UE, the MME shall include the "Homogenous Support of IMS Voice over PS Sessions" indication set to "Supported".
- if none of the TAs of the serving MME supports "IMS Voice over PS Sessions" for the UE, the MME shall include the "Homogenous Support of IMS Voice over PS Sessions" indication set to "Not supported".
- if "IMS Voice over PS Sessions" support is either non-homogeneous or unknown, the MME shall not include the "Homogenous Support of IMS Voice over PS Sessions" indication.
Regarding homogenous support/non-support of IMS Voice over PS session for all registered TAs of the UE, see clause 4.3.5.8.
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495b59b986f98d41912141cabbec196e
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23.401
|
4.3.5.9 Voice domain preference and UE's usage setting
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If the UE supports CS fallback, or the UE is configured to support IMS voice, or both, the UE shall include the information element "Voice domain preference and UE's usage setting" in Attach Request, Tracking Area Update Request and Routing Area Update Request messages. The purpose of this information element is to signal to the network the UE's usage setting and voice domain preference for E-UTRAN. The UE's usage setting indicates whether the UE behaves in a voice centric or data centric way (as defined in TS 23.221 [27]). The voice domain preference for E‑UTRAN indicates whether the UE is configured as CS Voice only, CS Voice preferred and IMS PS Voice as secondary, IMS PS Voice preferred and CS Voice as secondary, or IMS PS Voice only (as defined in TS 23.221 [27]).
In this Release of the specifications, inter-RAT mobility to/from the NB-IoT RAT is not supported, and GBR bearers are not supported in the NB-IoT RAT. Hence the UE should not include the "Voice domain preference and UE's usage setting" IE when sending an Attach Request or Tracking Area Update Request on the NB-IoT RAT.
NOTE: Depending on operator's configuration, the UE's usage setting and voice domain preference for E‑UTRAN can be used by the network to choose the RFSP Index in use (see clause 4.3.6). As an example, this enables the enforcement of selective idle mode camping over GERAN/UTRAN for voice centric UEs relying on CS Fallback for voice support in E‑UTRAN.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.5.10 Preferred and Supported Network Behaviour
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A UE includes in a Preferred Network Behaviour indication the Network Behaviour the UE can support and what it would prefer to use.
The Preferred Network Behaviour includes this information:
- Whether Control Plane CIoT EPS Optimisation is supported.
- Whether User Plane CIoT EPS Optimisation is supported.
- Whether Control Plane CIoT EPS Optimisation is preferred or whether User Plane Plane CIoT EPS Optimisation is preferred.
- Whether S1-U data transfer is supported.
- Whether SMS transfer without Combined Attach is requested.
- Whether Attach without PDN Connectivity is supported.
- Whether header compression for Control Plane CIoT EPS Optimisation is supported.
If SMS transfer without Combined EPS Attach is requested by the UE, a supporting MME provides SMS transfer without the UE performing the combined EPS attach specified in TS 23.272 [58]. An MME connected to NB-IoT should support SMS transfer without the UE being required to perform a Combined Attach.This feature is only available to UEs that only support NB-IoT.
If S1-U data transfer is supported is indicated by the UE, the UE supports data transfer that is not subject to CIoT EPS Optimisations. If the UE indicates support of User Plane CIoT EPS Optimisation then it shall also indicate support of S1-U data transfer.
If Attach without PDN connection is supported, the UE need not establish a PDN connection as part of the Attach procedure and the UE and MME may at any time release all the PDN connections and remain EPS attached.
The MME indicates the network behaviour the network accepts in the Supported Network Behaviour information. This indication is per TAI List. The MME may indicate one or more of the following:
- Whether Control Plane CIoT EPS Optimisation is supported.
- Whether User Plane CIoT EPS Optimisation is supported.
- Whether S1-U data transfer is supported.
- Whether SMS transfer without Combined Attach is accepted.
- Whether Attach without PDN Connectivity is supported.
- Whether header compression for Control Plane CIoT EPS Optimisation is supported.
If the MME indicates support of User Plane CIoT EPS Optimisation then it shall also indicate support of S1-U data transfer. If the UE and MME indicate support for User Plane CIoT EPS Optimisation, MME sets the UE User Plane CIoT Support Indicator to "supported" in S1-AP messages as defined in TS 36.413 [36].
For NB-IoT UEs that only support Control Plane CIoT EPS Optimisation, the MME shall include support for Control Plane CIoT EPS Optimisation in NAS accept messages.
A UE that supports the NB-IoT shall always indicate support for Control Plane CIoT EPS Optimisation.
In a network that supports Dedicated Core Networks (see clause 5.19), the Preferred Network Behaviour indication from the UE may be used to influence policy decisions that can cause rerouting of the Attach or TAU from an MME to another MME.
Other CIoT EPS Optimisations include "Attach without PDN connection establishment"; "PDN type = non-IP"; and "UE connection to SCEF". These features are requested by implicit and explicit signalling described within the relevant clauses of this TS.
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495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.6 Radio Resource Management functions
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Radio resource management functions are concerned with the allocation and maintenance of radio communication paths, and are performed by the radio access network. RRM includes both idle mode and connected mode. The RRM strategy in E-UTRAN may be based on user specific information.
To support radio resource management in E-UTRAN the MME provides the parameter 'Index to RAT/Frequency Selection Priority' (RFSP Index) to an eNodeB across S1. The RFSP Index is mapped by the eNodeB to locally defined configuration in order to apply specific RRM strategies. The RFSP Index is UE specific and applies to all the Radio Bearers. Examples of how this parameter may be used by the E-UTRAN:
- to derive UE specific cell reselection priorities to control idle mode camping.
- to decide on redirecting active mode UEs to different frequency layers or RATs.
To provide additional support to radio resource management in E-UTRAN, the MME may provide the parameter 'Additional RRM Policy Index' (ARPI) to an eNodeB across S1. The ARPI is mapped by the eNodeB to locally defined configuration in order to apply specific RRM strategies.
An example of how this parameter may be used by the E-UTRAN is:
- to prioritise the allocation of RAN resources to the set of UEs with the same ARPI.
The Serving PLMN can use the ARPI to carry information that is independent to the Reference SPID values documented in Informative Annex I of TS 36.300 [5].
The MME receives the subscribed RFSP Index and subscribed ARPI from the HSS (e.g., during the Attach procedure). For non-roaming subscribers the MME chooses the RFSP Index and ARPI in use according to one of the following procedures, depending on operator's configuration:
- the RFSP Index in use is identical to the subscribed RFSP Index, or
- the MME chooses the RFSP Index in use based on the subscribed RFSP Index, the locally configured operator's policies and the UE related context information available at the MME, including UE's usage setting and voice domain preference for E-UTRAN, if received during Attach and Tracking Area Update procedures (see clause 4.3.5.9).
NOTE: One example of how the MME can use the "UE voice capabilities and settings" is to select an RFSP value that enforces idle mode camping on 2G/3G for a UE acting in a "Voice centric" way and provisioned with "CS Voice preferred, IMS Voice as secondary", in order to minimize the occurrancy of RAT changes. Another example is the selection of an RFSP value that prevents idle mode camping on 2G for a UE provisioned with "IMS PS voice preferred, CS Voice as secondary" if other RATs supporting IMS Voice are available, as the UE would in such case always select the CS domain for its voice calls.
- the ARPI In Use is identical to the subscribed ARPI, or
- the MME chooses the ARPI in use based on the subscribed ARPI, the locally configured operator's policies and the UE related context information available at the MME.
For roaming subscribers the MME may alternatively choose the RFSP Index and ARPI in use based on the visited network policy, but can take input from the HPLMN into account (e.g., an RFSP Index value/ARPI value pre-configured per HPLMN, or a single RFSP Index value/single ARPI value to be used for all roamers independent of the HPLMN).
The MME forwards the RFSP Index and ARPI in use to the eNodeB across S1. The RFSP Index and ARPI in use is also forwarded from source eNodeB to target eNodeB when X2 is used for intra-E‑UTRAN handover, UE context retrieval, or, Dual Connectivity with a secondary RAN node.
The MME stores the subscribed RFSP Index and ARPI values received from the HSS and the RFSP Index and ARPI values in use. During the Tracking Area Update procedure, the MME may update the RFSP Index/ARPI value in use (e.g. the MME may need to update the RFSP Index/ARPI value in use if the UE related context information in the MME has changed). When the RFSP Index/ARPI value in use is changed, the MME immediately provides the updated RFSP Index/ARPI value in use to eNodeB by modifying an existing UE context or by establishing an new UE context in the eNodeB or by being configured to include the updated RFSP Index/ARPI value in use in the DOWNLINK NAS TRANSPORT message if the user plane establishment is not needed. During inter-MME mobility procedures, the source MME forwards both RFSP Index values and both ARPI values to the target MME. The target MME may replace the received RFSP Index and ARPI values in use with a new RFSP Index value in use or new ARPI value in use that is based on the operator's policies and the UE related context information available at the target MME.
The S1 messages that transfer the RFSP Index and ARPI to the eNodeB are specified in TS 36.413 [36]. Refer to TS 36.300 [5] for further information on E-UTRAN.
To support a RAN with a mixture of RAN nodes that support and do not support the ARPI, the MME sends the ARPI In Use in the S1 interface PATCH SWITCH ACKNOWLEDGEMENT and HANDOVER REQUEST messages.
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495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.7 Network management functions
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495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.7.1 General
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Network management functions provide mechanisms to support O&M functions related to the Evolved Packet System.
4.3.7.1a GTP-C signalling based Load and Overload Control
4.3.7.1a.1 GTP-C Load Control
GTP-C Load Control feature is an optional feature which allows a GTP control plane node to send its Load Control Information to a peer GTP control plane node which the receiving GTP control plane peer node uses to augment existing GW selection procedure (i.e. as described in "PDN GW Selection" and "Serving GW Selection" according to clauses 4.3.8.1, and 4.3.8.2 respectively). Load Control Information reflects the operating status of the resources of the originating GTP control plane node.
NOTE 1: How a node computes its Load Control Information is implementation dependent.
Where certain pre-condition as described in clause 12.2.4.1 of TS 29.274 [43], is applicable, an optional feature APN level load control may be supported and activated in the network. If this feature is activated, the PDN GW may convey the Load Control Information at APN level (reflecting the operating status of the resources at the APN level), besides at node level.
GTP-C Load Control feature allows the Serving GW to send its Load Control Information to the MME/SGSN.
GTP-C Load Control feature also allows the PDN GW to send its Load Control Information to the MME/SGSN via a Serving GW.
Upon receiving Load Control Information the MME/SGSN supporting GTP-C Load Control feature uses it according to clauses 4.3.8.1, and 4.3.8.2 for "PDN GW Selection" and "Serving GW Selection" respectively.
A node supporting GTP-C Load Control feature sends Load Control Information in any GTP control plane request or response message such that exchange of Load Control Information does not trigger extra signalling.
A node supporting GTP-C Load Control feature sends Load Control Information to a peer GTP control node based on whether local configuration allows for it.
A node supporting GTP-C Load Control feature may decide to send different values of Load Control Information on inter-network (roaming) and on intra-network (non-roaming) interfaces based on local configuration.
Local configuration may allow the VPLMN to decide whether or not to act upon Load Control Information sent from a peer GTP control plane node in the HPLMN.
NOTE 2: Refer to clause 12 of TS 29.274 [43] for the details, such as exact format of the Load Control Information, mechanisms to discover the support of the feature by the peer node, interfaces for which this feature is applicable, APN level load control, etc.
4.3.7.1a.2 GTP-C Overload Control
GTP-C Overload Control feature is an optional feature. Nodes using GTP control plane signalling may support communication of Overload Control Information in order to mitigate overload situation for the overloaded node through actions taken by the peer node(s). This feature is supported over S4, S11, S5 and S8 interfaces via GTPv2 control plane protocol.
A GTP-C node is considered to be in overload when it is operating over its nominal capacity resulting in diminished performance (including impacts to handling of incoming and outgoing traffic). Overload Control Information reflects an indication of when the originating node has reached such situation. This information, when transmitted between GTP-C nodes may be used to reduce and/or throttle the amount of GTP-C signalling traffic between these nodes. As such, the Overload Control Information provides guidance to the receiving node to decide actions which leads to mitigation towards the sender of the information.
NOTE 1: How a node determines its Overload Control Information is implementation dependent.
The Overload Control Information may convey information regarding the node itself and/or regarding specific APN(s) status. In order to mitigate overload,
- it shall be possible to signal control information about the overload of a GTP-C node (e.g. S-GW, P-GW);
- the PDN GW may detect overload for certain APNs, e.g. based on Diameter overload indication received from a PCRF or from an external AAA server, or e.g. based on shortage of resources for an APN (IP address pool). It shall be possible to signal appropriate control information about the APN status in addition to the mechanism described in clause 4.3.7.5.
For a given APN, the PDN GW shall either activate the congestion control by conveying the Overload Control Information at APN level or by conveying the "PDN GW back-off time" (as specified in clause 4.3.7.5), but not both at the same time, as specified in more detail in clause 12.3.8 of TS 29.274 [43].
GTP-C Overload Control feature allows the MME/SGSN to send its Overload Control Information to the PDN GW via Serving GW.
GTP-C Overload Control feature allows the Serving GW to send its Overload Control Information to the MME/SGSN and P-GW.
GTP-C Overload Control feature also allows the PDN GW to send its Overload Control Information to the MME/SGSN via a Serving GW.
GTP-C overload Control feature should continue to allow for preferential treatment of priority users (eMPS) and emergency services as per existing specifications.
An MME/SGSN may during ESM and EMM procedures apply certain restrictions towards GWs (Serving GW and/or PDN GW as applicable) that have indicated overload, e.g.:
- reject EPS Session Management requests from the UE (e.g. PDN Connectivity, Bearer Resource Allocation or Bearer Resource Modification Requests) with a Session Management back-off timer as described in clause 4.3.7.4.2;
- reject Mobility Management signalling requests from UEs (such as Attach, Detach, Service Request, Tracking Area Update) with a Mobility Management back-off timer (e.g. reject Service Request requiring to activate user plane bearers in an overloaded SGW) as described in clause 4.3.7.4.2;
- reject or accept requests for data transmission via Control Plane CIoT EPS Optimisation from UEs (e.g. Control Plane Service Request and ESM Data Transport) with a Control Plane data back-off timer as described in clause 4.3.7.4.2.7;
- may reduce/throttle messages towards the GWs indicating overload status;
- other implementation specific mechanisms, which are outside the scope of 3GPP specifications.
A PDN GW may take the following actions for MME/SGSN which have indicated overload:
- Limit or completely block non-GBR dedicated bearer establishment;
- Limit or completely block all Dedicated Bearer establishments or modification, except QCI=1 bearers;
- Limit or completely block all Dedicated Bearer establishments, including the QCI=1 bearers;
- other implementation specific mechanisms, which are outside the scope of 3GPP specifications.
A node supporting GTP-C Overload Control feature sends Overload Control Information in any GTP control plane request or response message such that exchange of Overload Control Information does not trigger extra signalling.
The computation and transfer of the Overload Control Information shall not add significant additional load to the node itself and to its corresponding peer nodes. The calculation of Overload Control Information should not severely impact the resource utilization of the node.
Based on local policies/configuration, a GTP-C node may support Overload Control feature and act upon or ignore Overload Control Information in the VPLMN when received from HPLMN and in the HPLMN when received from VPLMN. When this feature is supported, a GTP-C node may decide to send different values of Overload Control Information on inter-network (roaming) and on intra-network (non-roaming) interfaces based on local policies/configuration.
NOTE 2: Refer to clause 12 of TS 29.274 [43] for the details, such as exact format of the Overload Control Information, mechanisms to discover the support of the feature by the peer node, interfaces for which this feature is applicable, APN level overload control, etc.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.7.2 Load balancing between MMEs
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The MME Load Balancing functionality permits UEs that are entering into an MME Pool Area to be directed to an appropriate MME in a manner that achieves load balancing between MMEs. This is achieved by setting a Weight Factor for each MME, such that the probability of the eNodeB selecting an MME is proportional to its Weight Factor. The Weight Factor is typically set according to the capacity of an MME node relative to other MME nodes. The Weight Factor is sent from the MME to the eNodeB via S1-AP messages (see TS 36.413 [36]). If a HeNB GW is deployed, the Weight Factor is sent from the MME to the HeNB GW.
NOTE 1: An operator may decide to change the Weight Factor after the establishment of S1-MME connectivity as a result of changes in the MME capacities. E.g., a newly installed MME may be given a very much higher Weight Factor for an initial period of time making it faster to increase its load.
NOTE 2: It is intended that the Weight Factor is NOT changed frequently. e.g. in a mature network, changes on a monthly basis could be anticipated, e.g. due to the addition of RAN or CN nodes.
In some networks, the eNodeB may be configured to select specific MME for UEs configured for low access priority with a different load balance to that used for MME selection for other UEs.
NOTE 3: The eNodeB can determine whether or not the "UE is configured for low access priority" from information received in the RRC establishment or RRC resume signalling.
When DCNs are used, load balancing by eNodeB is only performed between MMEs that belong to the same DCN within the same MME pool area, i.e. MMEs with the same PLMN and MMEGI value. When an MME serves multiple DCNs and one DCN is supported by multiple MMEs, in order to achieve load balancing across the MMEs of the same MME pool area supporting the same DCN, each DCN supported by this MME may have its own Weight Factor (Weight Factor per DCN). The Weight Factor per DCN is set according to the capacity of an MME node for a specific DCN relative to other MME nodes' capacity for that DCN within the same MME pool area. The eNodeB is provided with per DCN Weight Factors, if any, by the connected MMEs at the set-up of the S1 connection. The DCN Load Balancing functionality permits UEs that are entering into a pool area or being re-directed to an appropriate DCN to be distributed in a manner that achieves load balancing between the CN nodes of the same DCN. The eNodeB may be configured to select MME(s) from a specific CN for UEs configured for low access priority only for the case that no other information and configuration is available for selecting an MME from a specific DCN.
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23.401
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4.3.7.3 Load re-balancing between MMEs
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The MME Load Re-balancing functionality permits UEs that are registered on an MME (within an MME Pool Area) to be moved to another MME.
NOTE 1: An example use for the MME Load Re-balancing function is for the O+M related removal of one MME from an MME Pool Area.
NOTE 2: Typically, this procedure should not be used when the MME becomes overloaded because the Load Balancing function should have ensured that the other MMEs in the pool area are similarly overloaded.
The eNodeBs may have their Load Balancing parameters adjusted beforehand (e.g. the Weight Factor is set to zero if all subscribers are to be removed from the MME, which will route new entrants to the pool area into other MMEs).
In addition the MME may off-load a cross-section of its subscribers with minimal impacts on the network and users (e.g. the MME should avoid offloading only the low activity users while retaining the high activity subscribers. Gradual rather than sudden off-loading should be performed as a sudden re-balance of large number of subscribers could overload other MMEs in the pool. With minimal impact on network and the user's experience, the subscribers should be off-loaded as soon as possible). The load re-balancing can off-load part of or all the subscribers.
To off-load ECM-CONNECTED mode UEs, the MME initiates the S1 Release procedure with release cause "load balancing TAU required" (clause 5.3.5). The S1 and RRC connections are released and the UE initiates a TAU but provides neither the S-TMSI nor the GUMMEI to eNodeB in the RRC establishment.
NOTE 3: Special care needs to be taken when offloading Relay Nodes. This is because there may be UEs connected to the RN and some of these UEs may be registered on other MMEs.
The MME should not release all S1 connections which are selected to be released immediately when offloading is initiated. The MME may wait until the S1 Release is performed due to inactivity. When the MME is to be offloaded completely the MME can enforce an S1 Release for all remaining UEs that were not offloaded by normal TAU procedures or by S1 releases caused by inactivity.
To off-load UEs which perform TA Updates or Attaches initiated in ECM-IDLE mode, the MME completes that procedure and the procedure ends with the MME releasing S1 with release cause "load balancing TAU required". The S1 and RRC connections are released and the UE initiates a TAU but provides neither the S-TMSI nor the GUMMEI to eNodeB in the RRC establishment.
When the UE provides neither the S-TMSI nor the GUMMEI in the RRC establishment, the eNodeB should select an MME based on the Weight Factors of the MMEs in the pool.
To off-load UEs in ECM-IDLE state without waiting for the UE to perform a TAU or perform Service request and become ECM‑CONNECTED, the MME first pages UE to bring it to ECM-CONNECTED state. If paging the UE fails and ISR is activated, the MME should adjust its paging retransmission strategy (e.g. limit the number of short spaced retransmissions) to take into account the fact that the UE might be in GERAN/UTRAN coverage.
Hardware and/or software failures within an MME may reduce the MME's load handling capability. Typically such failures should result in alarms which alert the operator/O+M system. Only if the operator/O+M system is sure that there is spare capacity in the rest of the pool, the operator/O+M system might use the load re-balancing procedure to move some load off this MME. However, extreme care is needed to ensure that this load re-balancing does not overload other MMEs within the pool area (or neighbouring SGSNs) as this might lead to a much wider system failure.
When the Dedicated Core Network (DCN) feature is used, the DCN load re-balancing functionality permits UEs that are registered on an MME in the DCN (within a pool area) to be moved to another MME in the same DCN in a manner that achieves load balancing between the CN nodes of the DCN and pool area. The DCN load re-balancing is triggered by the source MME (within a DCN). The details are as follows:
- If the UE is in ECM-IDLE state, the NAS Message Redirection procedure (see clause 5.19.1) is triggered at the next intra-MME Tracking Area Update Request enabling eNodeB to load balance between MMEs of the same DCN. To off-load UEs in ECM-IDLE state without waiting for the UE to perform a TAU or perform Service request, the MME first pages the UE to bring it to ECM-CONNECTED state and proceeds as described for the ECM-CONNECTED case below.
- If the UE is in ECM-CONNECTED state, the MME performs the GUTI reallocation procedure, includes the unchanged GUTI of the UE and a non-broadcast TAI to induce the UE to perform a TAU procedure, and forces the UE to go to ECM-IDLE state. During the subsequent TAU procedure the MME uses the NAS Message Redirection procedure (see clause 5.19.1) to redirect the UE to another MME within the same DCN.
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4.3.7.4 MME control of overload
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23.401
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4.3.7.4.1 General
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The MME shall contain mechanisms for avoiding and handling overload situations. These can include the use of NAS signalling to reject NAS requests from UEs.
In addition, under unusual circumstances, the MME shall restrict the load that its eNodeBs are generating on it if it is configured to enable the overload restriction. This can be achieved by the MME invoking the S1 interface overload procedure (see TS 36.300 [5] and TS 36.413 [36]) to all or to a proportion of the eNodeB's with which the MME has S1 interface connections. To reflect the amount of load that the MME wishes to reduce, the MME can adjust the proportion of eNodeBs which are sent S1 interface OVERLOAD START message, and the content of the OVERLOAD START message.
The MME should select the eNodeBs at random (so that if two MMEs within a pool area are overloaded, they do not both send OVERLOAD START messages to exactly the same set of eNodeBs).
The MME may optionally include a Traffic Load Reduction Indication in the OVERLOAD START message. In this case the eNodeB shall, if supported, reduce the type of traffic indicated according the requested percentage (see TS 36.413 [36]).
NOTE 1: The MME implementation may need to take into account the fact that eNodeBs compliant to Release 9 and earlier version of the specifications do not support the percentage overload indication.
An MME supporting Control Plane CIoT EPS Optimisation may include an indication in the OVERLOAD START message indicating overload from data transfers via Control Plane CIoT EPS Optimisation.
Using the OVERLOAD START message, the MME can request the eNodeB to:
- reject RRC connection requests that are for non-emergency, non-exception reporting and non-high priority mobile originated services; or
NOTE 2: This blocks PS service and service provided by MSC following an EPS/IMSI attach procedure.
- reject new RRC connection requests for EPS Mobility Management signalling (e.g. for TA Updates) for that MME;
- only permit RRC connection requests for emergency sessions and mobile terminated services for that MME. This blocks emergency session requests from UEs with USIMs provisioned with Access Classes 11 and 15 when they are in their HPLMN/EHPLMN and from UEs with USIMs provisioned with Access Classes 12, 13 and 14 when they are in their home country (defined as the MCC part of the IMSI, see TS 22.011 [67]); or.
NOTE 3: The MME can restrict the number of responses to paging by not sending paging messages for a proportion of the events that initiate paging. As part of this process, the MME can provide preference for paging UEs with Emergency Bearer Services and terminations associated with MPS ARP.
- only permit RRC connection requests for high priority sessions, exception reporting and mobile terminated services for that MME;
- reject new RRC connection requests from UEs that access the network with low access priority;
- not accept RRC connection requests with RRC establishment cause "mo-data" or "delayTolerantAccess" from UEs that only support Control Plane CIoT EPS Optimisation.
NOTE 4: The RRC connection requests listed in this clause also include the request for RRC Connection Resume.
When rejecting an RRC connection request for overload reasons the eNodeB indicates to the UE an appropriate timer value that limits further RRC connection requests for a while.
An eNodeB supports rejecting of RRC connection establishments for certain UEs as specified in TS 36.331 [37]. Additionally, an eNodeB provides support for the barring of UEs configured for Extended Access Barring, as described in TS 22.011 [67]. These mechanisms are further specified in TS 36.331 [37]. If the UE is camping on NB-IoT, Extended Access Barring does not apply.
An eNodeB may initiate Extended Access Barring when:
- all the MMEs connected to this eNodeB request to restrict the load for UEs that access the network with low access priority; or
- requested by O&M.
If an MME invokes the S1 interface overload procedure to restrict the load for UEs that access the network with low access priority, the MME should select all eNodeBs with which the MME has S1 interface connections. Alternatively, the selected eNodeBs may be limited to a subset of the eNodeBs with which the MME has S1 interface connection (e.g. particular location area or where devices of the targeted type are registered).
During an overload situation the MME should attempt to maintain support for emergency bearer services (see clause 4.3.12) and for MPS (see clause 4.3.18).
When the MME is recovering, the MME can either:
- send OVERLOAD START messages with new percentage value that permit more traffic to be carried, or
- the MME sends OVERLOAD STOP messages.
to some, or all, of the eNodeB(s).
In addition, to protect the network from overload the MME has the option of rejecting NAS request messages which include the low access priority indicator before rejecting NAS request messages without the low access priority indicator (see clause 4.3.7.4.2 for more information).
NOTE 5: It cannot be guaranteed that voice services will be available for mobile terminated calls while the Mobility Management back-off timer is running. It is recommended, that UEs requiring voice services are not configured for low access priority.
In addition, for UEs that don't support the Service Gap Control feature (see clause 4.3.17.9), the MME may use "General NAS level Mobility Management control" as defined in clause 4.3.7.4.2.1.
4.3.7.4.1a Throttling of Downlink Data Notification Requests
Under unusual circumstances (e.g. when the MME load exceeds an operator configured threshold), the MME may restrict the signalling load that its SGWs are generating on it, if configured to do so.
The MME can reject Downlink Data Notification requests for non-priority traffic for UEs in idle mode or to further offload the MME, the MME can request the SGWs to selectively reduce the number of Downlink Data Notification requests it sends for downlink non-priority traffic received for UEs in idle mode according to a throttling factor and for a throttling delay specified in the Downlink Data Notification Ack message.
The SGW determines whether a bearer is to be subjected to the throttling of Downlink Data Notification Requests on the basis of the bearer's ARP priority level and operator policy (i.e. operator's configuration in the SGW of the ARP priority levels to be considered as priority or non- priority traffic). While throttling, the SGW shall throttle the Downlink Data Notification Requests for low and normal priority bearers by their priority. The MME determines whether a Downlink Data Notification request is priority or non-priority traffic on the basis of the ARP priority level that was received from the SGW and operator policy.
If ISR is not active for the UE, during the throttling delay, the SGW drops downlink packets received on all its non-priority bearers for UEs known as not user plane connected (i.e. the SGW context data indicates no downlink user plane TEID) served by that MME in proportion to the throttling factor, and sends a Downlink Data Notification message to the MME only for the non throttled bearers.
If ISR is active for the UE, during the throttling delay, the SGW does not send DDN to the MME and only sends the DDN to the SGSN. If both MME and SGSN are requesting load reduction, the SGW drops downlink packets received on all its non-priority bearers for UEs known as not user plane connected (i.e. the SGW context data indicates no downlink user plane TEID) in proportion to the throttling factors.
The SGW resumes normal operations at the expiry of the throttling delay. The last received value of the throttling factor and throttling delay supersedes any previous values received from that MME. The reception of a throttling delay restarts the SGW timer associated with that MME.
4.3.7.4.1b Throttling of NIDD Submit Requests
Under unusual circumstances (e.g. when the MME load exceeds an operator configured threshold), the MME may restrict NIDD Submit Request messages that its SCEFs are generating on it, if configured to do so.
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4.3.7.4.2 NAS level congestion control
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4.3.7.4.2.1 General
NAS level congestion control contains the functions: "APN based congestion control" and "General NAS level Mobility Management control".
The use of the APN based congestion control is for avoiding and handling of EMM and ESM signalling congestion associated with UEs with a particular APN. Both UEs and network shall support the functions to provide APN based EMM and ESM congestion control.
The MME may detect the NAS signalling congestion associated with the APN and start and stop performing the APN based congestion control based on criteria such as:
- Maximum number of active EPS bearers per APN;
- Maximum rate of EPS Bearer activations per APN;
- One or multiple PDN GWs of an APN are not reachable or indicated congestion to the MME;
- Maximum rate of MM signalling requests associated with the devices with a particular subscribed APN; and/or
- Setting in network management.
The MME may detect the NAS signalling congestion associated with the UEs belonging to a particular group. The MME may start and stop performing the group specific NAS level congestion control based on criteria such as:
- Maximum rate of MM and SM signalling requests associated with the devices of a particular group; and/or
- Setting in network management.
The MME may detect the NAS signalling congestion associated with the UEs that belong to a particular group and are subscribed to a particular APN. The MME may start and stop performing the APN and group specific NAS level congestion control based on criteria such as:
- Maximum number of active EPS bearers per group and APN;
- Maximum rate of MM and SM signalling requests associated with the devices of a particular group and a particular subscribed APN; and/or
- Setting in network management.
The MME should not apply NAS level congestion control for high priority access and emergency services.
With General NAS level Mobility Management control, the MME may also use the reject of NAS level Mobility Management signalling requests under general congestion conditions such as detecting congestion of one or several DCNs in an MME serving multiple DCNs.
In addition, for UEs that don't support the Service Gap Control feature (see clause 4.3.17.9), the MME may return a Mobility Management back-off timer to the UE in responses to requests where the intention is to send MO data or re-attach with PDN connectivity when the Service gap timer for the UE is running at the MME.
4.3.7.4.2.2 APN based Session Management congestion control
The APN based Session Management congestion control may be activated by MME due to e.g. congestion situation at MME, or by OAM at MME, or by a restart or recovery condition of a PDN GW, or by a partial failure or recovery of a PDN GW for a particular APN(s).
The MME may reject the EPS Session Management (ESM) requests from the UE (e.g. PDN Connectivity, or Bearer Resource Allocation Requests) with a Session Management back-off timer when ESM congestion associated with the APN is detected. If the UE provides no APN, then the MME uses the APN which is used in PDN GW selection procedure.
The MME may deactivate PDN connections belonging to a congested APN by sending the NAS Deactivate EPS Bearer Context Request message to the UE with a Session Management back-off timer. If Session Management back-off timer is set in the NAS Deactivate EPS Bearer Context Request message then the cause "reactivation requested" should not be set.
NOTE 1: UEs that don't support the Session Management back-off timer (including earlier release of UE) might contribute to increasing the signalling load in the MME by reattempting Session Management procedure.
The MME may store a Session Management back-off time per UE and APN when congestion control is active for an APN if a request without the low access priority indicator is rejected by the MME. The MME may immediately reject any subsequent request from the UE targeting to the APN before the stored Session Management back-off time is expired. If the MME stores the Session Management back-off time per UE and APN and the MME decides to send a Session Management Request message to a UE connected to the congested APN (e.g. due to decreased congestion situation), the MME shall clear the Session Management back-off time prior to sending any Session Management Request message to the UE.
NOTE 2: The above functionality is to diminish the performance advantage for UEs that do not support the NAS level back-off timer (e.g. pre-Rel‑10 UEs) compared to UEs that do support it.
Upon reception of the Session Management back-off timer in the EPS Session Management reject message or in the NAS Deactivate EPS Bearer Context Request message, the UE shall take the following actions until the timer expires:
- If APN is provided in the rejected EPS Session Management Request message or if the Session Management back-off timer is received in the NAS Deactivate EPS Bearer Context Request message, the UE shall not initiate any Session Management procedures for the congested APN. The UE may initiate Session Management procedures for other APNs.
- If APN is not provided in the rejected EPS Session Management Request message, the UE shall not initiate any Session Management requests of any PDN type without APN. The UE may initiate Session Management procedures for specific APN.
- Cell/TA/PLMN/RAT change do not stop the Session Management back-off timer.
- The UE is allowed to initiate the Session Management procedures for high priority access and emergency services even when the Session Management back-off timer is running.
- The UE is allowed to initiate Bearer Resource Modification procedure to report 3GPP PS Data Off status change when the EPS Session Management back off timer is running.
- If the UE receives a network initiated EPS Session Management Request message for the congested APN while the Session Management back-off timer is running, the UE shall stop the Session Management back-off timer associated with this APN and respond to the MME.
- If the UE is configured with a permission for overriding low access priority and the Session Management back-off timer is running due to a reject message received in response to a request with low access priority, the upper layers in the UE may request the initiation of Session Management procedures without low access priority.
The UE is allowed to initiate PDN disconnection procedure (e.g. sending PDN Disconnection Request) when the EPS Session Management back off timer is running.
NOTE 3: The UE does not delete the related Session Management back-off timer when disconnecting a PDN connection.
The UE shall support a separate Session Management back-off timer for every APN that the UE may activate.
To avoid that large amounts of UEs initiate deferred requests (almost) simultaneously, the MME should select the Session Management back-off timer value so that deferred requests are not synchronized.
The APN based Session Management congestion control is applicable to the NAS ESM signalling initiated from the UE in the control plane. The Session Management congestion control does not prevent the UE to send and receive data or initiate Service Request procedures for activating user plane bearers towards the APN(s) that are under ESM congestion control.
4.3.7.4.2.3 APN based Mobility Management congestion control
The MME may perform the APN based congestion control for UEs with a particular subscribed APN by rejecting Attach procedures with a Mobility Management back-off timer.
When congestion control is active for UEs with a particular subscribed APN, a Mobility Management back-off timer may be sent by the MME to UE.
If MME maintains the UE context, the MME may store the back-off time per UE if a request without the low access priority indicator is rejected by the MME. The MME may immediately reject any subsequent request from the UE before the stored back-off time is expired.
NOTE 1: The above functionality is to diminish the performance advantage for UEs that do not support the NAS level back-off timer (e.g. pre-Rel‑10 UEs) compared to UEs that do support it.
After rejecting Attach Requests, the MME should keep the Subscriber Data for some time. This allows for rejection of subsequent requests without HSS signalling when the congestion situation resulting from UEs with a particular subscribed APN persists.
NOTE 2: Prior to the reject of attach messages of a UE by the MME, Subscriber Data for a UE may be present at the MME because it was not deleted after the UE's detach. In this case when APN based congestion control is active for a particular APN in the MME, the first reject of an attach message by the MME for this UE, may be done without HSS signalling as well.
While the Mobility Management back-off timer is running, the UE shall not initiate any NAS request for Mobility Management procedures. However, the UE is allowed to initiate the Mobility Management procedures for high priority access and emergency services even when the Mobility Management back-off timer is running. While the Mobility Management back-off timer is running, the UE is allowed to perform Tracking Area Update if it is already in connected mode.
While the Mobility Management back-off timer is running, the UE configured with a permission for overriding low access priority is allowed to initiate the Mobility Management procedures without low access priority if the Mobility Management back-off timer was started due to a reject message received in response to a request with low access priority and the upper layers in the UE request to activate a PDN connection without low access priority or the UE has an activated PDN connection that is not with low access priority.
To avoid that large amounts of UEs initiate deferred requests (almost) simultaneously, the MME should select the Mobility Management back-off timer value so that deferred requests are not synchronized.
NOTE 3: When receiving the Mobility Management back-off timer the UE behaviour is not APN specific.
4.3.7.4.2.4 General NAS level Mobility Management congestion control
Under general overload conditions the MME may reject Mobility Management signalling requests from UEs. When a NAS request is rejected, a Mobility Management back-off timer may be sent by the MME and MME may store the back-off time per UE if a request without the low access priority indicator is rejected by the MME and if MME maintains the UE context. The MME may immediately reject any subsequent request from the UE before the stored back-off time is expired. While the Mobility Management back-off timer is running, the UE shall not initiate any NAS request for Mobility Management procedures except for Detach procedure and except for high priority access, emergency services, mobile terminated services and to inform of an unavailability period (see clause 4.13.8.2). After any such Detach procedure, the back-off timer continues to run. While the Mobility Management back-off timer is running, the UE is allowed to perform Tracking Area Update if it is already in connected mode. If the UE receives a paging request from the MME while the Mobility Management back off timer is running, the UE shall stop the Mobility Management back-off timer and initiate the Service Request procedure or the Tracking Area Update procedure as described in clause 5.3.3.0.
While the Mobility Management back-off timer is running, the UE configured with a permission for overriding low access priority is allowed to initiate the Mobility Management procedures without low access priority if the Mobility Management back-off timer was started due to a reject message received in response to a request with low access priority and the upper layers in UE request to establish a PDN connection without low access priority or the UE has an established PDN connection that is without low access priority.
While the Mobility Management back-off timer is running, the UE configured with permission for sending exception reporting is allowed to initiate the Control Plane Service Request procedure for exception reporting. If the Mobility Management back-off timer was started due to a reject message received in response to a request for exception reporting, the UE shall not initiate the Control Plane Service Request procedure for exception reporting while the Mobility Management back-off timer is running.
The Mobility Management back-off timer shall not impact Cell/RAT and PLMN change. Cell/RAT and TA change do not stop the Mobility Management back-off timer. The Mobility Management back-off timer shall not be a trigger for PLMN reselection. The back-off timer is stopped as defined in TS 24.301 [46] when a new PLMN that is not an equivalent PLMN is accessed.
To avoid that large amounts of UEs initiate deferred requests (almost) simultaneously, the MME should select the Mobility Management back-off timer value so that the deferred requests are not synchronized.
When the UE receives a handover command, the UE shall proceed with the handover procedure regardless of whether Mobility Management back-off timer is running.
The MME should not reject Tracking Area Update procedures that are performed when the UE is already in connected mode or when the UE is indicating unavailability period.
For idle mode inter CN node mobility, the MME may reject Tracking Area Update procedures and include a Mobility Management back off timer value in the Tracking Area Reject message.
If the MME rejects Tracking Area Update request or Service request with a Mobility Management back-off timer which is larger than the sum of the UE's periodic TAU timer plus the Implicit Detach timer, the MME should adjust the mobile reachable timer and/or Implicit Detach timer such that the MME does not implicitly detach the UE while the Mobility Management back-off timer is running.
NOTE: This is to minimize unneeded signalling after the Mobility Management back-off timer expires.
4.3.7.4.2.5 Group specific NAS level congestion control
The group specific NAS level congestion control applies to a specific group of UEs. Each group has a group identifier assigned.
A UE belongs to a group, if the corresponding group identifier is stored in the UE's subscription data in the HSS. A UE may belong to multiple groups and the MME may perform the Group specific NAS level congestion control to an UE as described below independent of whether Group specific NAS level congestion control is activated for one, multiple, or all groups the UE belongs to. The group identifier shall be stored per UE in the HSS and obtained by the MME as part of normal HSS signalling. A UE is not aware of a group subscription.
The group specific NAS level congestion control may be activated for Session Management signalling, or for Mobility Management signalling, or both. The group specific NAS level congestion control is activated based on operator policies.
When the group specific NAS level congestion control for Session Management signalling is active for a particular group, the MME's behaviour is similar to that in clause 4.3.7.4.2.2, with the following modifications:
- MME may apply ESM congestion control to all subscribed APNs for UEs that belong to this particular group.
NOTE: How the MME applies ESM congestion control to all subscribed APNs is left to Stage 3.
- The MME rejects the EPS Session Management (ESM) request(s) from the UE belonging to this particular group (e.g. PDN Connectivity, or Bearer Resource Allocation Requests) with a Session Management back-off timer.
When group specific NAS level congestion control for Mobility Management signalling is active for a particular group, the MME's behaviour is similar to that in clause 4.3.7.4.2.3, but applied to UEs subscribed to this particular group rather that subscribed to a particular APN.
Group specific NAS level congestion control is performed at the MME based on the UE's subscription information provided by the HSS. There is no impact on the UE, and hence, UE's behaviour as described in clauses 4.3.7.4.2.2 and 4.3.7.4.2.3 does not change.
4.3.7.4.2.6 APN and group specific NAS level congestion control
The APN and group specific NAS level congestion control is the intersection of APN specific NAS level congestion control and Group specific NAS level congestion control, i.e. it applies to a specific group of UEs with a particular subscribed APN. Each group of UEs has a group identifier assigned and stored in the HSS.
A UE may belong to multiple groups and the MME may perform the APN and group specific NAS level congestion control to an UE as described below independent of whether the APN and group specific NAS level congestion control is activated for one, multiple or all groups the UE belongs to. The group identifier(s) shall be stored per UE in the HSS and obtained by the MME as part of normal HSS signalling. A UE is not aware of the group identifier(s) that the UE belongs to.
The APN and group specific NAS level congestion control may be activated for Session Management signalling, or for Mobility Management signalling, or both. The APN and group specific NAS level congestion control is activated based on operator policies.
When the APN and group specific NAS level congestion control for Session Management signalling is activated for a UE belonging to a particular group and initiating signalling to a particular APN, the MME's behaviour is similar to that in clause 4.3.7.4.2.2, with the following modifications:
- The EPS Session Management (ESM) congestion control is applied to this particular APN, and for UEs belonging to this particular group,
- The MME may reject ESM requests from the UEs belonging to this particular group and attaching to this particular APN (e.g. PDN Connectivity, or Bearer Resource Allocation Requests) with a Session Management back-off timer. If the UE provides no APN, then the MME uses the APN which is used in PDN GW selection procedure.
- The MME may deactivate PDN connections of the UEs, belonging to this particular group and attaching to this particular APN, by sending the NAS Deactivate EPS Bearer Context Request message to the UE with a Session Management back-off timer.
When the APN and group specific NAS level congestion control for Mobility Management signalling is activated for a UE belonging to a particular group and with a particular subscribed APN, the MME's behaviour is similar to that in clause 4.3.7.4.2.3, but applied to UEs with this particular subscribed APN and belonging to this particular group.
APN and group specific NAS level congestion control is performed at the MME based on the UE's subscription information provided by the HSS. There is no impact on the UE, and hence, UE's behaviour described in clauses 4.3.7.4.2.2 and 4.3.7.4.2.3 does not change.
4.3.7.4.2.7 Control Plane data specific NAS level congestion control
Under overload conditions the MME may restrict requests from UEs for data transmission via Control Plane CIoT EPS Optimisation. A Control Plane data back-off timer may be returned by the MME (e.g.in Attach/TAU/RAU Accept messages, Service Reject message or Service Accept message). While the Control Plane data back-off timer is running, the UE shall not initiate any data transfer via Control Plane CIoT EPS Optimisation, i.e. the UE shall not send any Control Plane Service Request with ESM Data Transport message as defined in TS 24.301 [46]. The MME shall store the Control Plane data back-off timer per UE and shall reject any further request (other than exception reporting and a response to paging) for data transmission via Control Plane Service Request from that UE while the Control Plane data back-off timer is still running.
NOTE 1: The Control Plane data back-off timer does not affect any other mobility management or session management procedure.
NOTE 2: The Control Plane data back-off timer does not apply to user plane data communication.
If the UE is allowed to send exception reporting, the UE may initiate Control Plane Service Request for exception reporting even if Control Plane data back-off timer is running.
The UE may respond with Control Plane Service Request without ESM Data Transport to a paging even if the Control Plane data back-off timer is running.
If the MME receives a Control Plane Service Request in reponse to paging, and the MME has a Control Plane data back-off timer running for the UE, and the MME is not overloaded, and MME decides to accept the Control Plane Service Request, then the MME shall respond with Service Accept message without the Control Plane data back-off timer and stop the Control Plane data back-off timer. If the UE receives a Service Accept message without the Control Plane data back-off timer from the MME while the Control Plane data back-off timer is running, the UE shall stop the Control Plane data back-off timer. The Control Plane data back-off timer in the UE and the MME is stopped at PLMN change.
If the MME receives a Control Plane Service Request with ESM Data Transport message, and decides to send the UE a Control Plane data back-off timer, the MME may decide to process the Control Plane Service Request with ESM Data Transport message, i.e. decrypt and forward the data payload, or not based on the following:
- If the UE has additionally indicated in a NAS Release Assistance Information in the NAS PDU that no further Uplink or Downlink Data transmissions are expected, then the MME may process (integrity check/decipher/forward) the received Control Plane data packet, and send SERVICE ACCEPT to the UE with Control Plane data back-off timer. The UE interprets this as successful transmission of the Control Plane data packet and starts the Control Plane data back-off timer.
- For all other cases, the MME may decide to not process the received control plane data packet and sends SERVICE REJECT to the UE with Control Plane data back-off timer. The UE interprets this indication as unsuccessful delivery of the control plane data packet and starts the Control Plane data back-off timer. Then MME may take into consideration whether the PDN Connection is set to Control Plane only to make the decision whether to reject the packet and send SERVICE REJECT or move the PDN connection to user plane and process the data packet.
- Alternatively, if UE has not provided in the in Control Plane service request the NAS Release Assistance Information, and the EPS bearer belongs to a PDN connection not set to Control Plane only, and UE supports User Plane CIoT Optimisation (or legacy S1-U), then the MME may initiate establishment of S1-U bearer during Data Transport in Control Plane CIoT EPS Optimisation (according to the procedure defined in clause 5.3.4B.4). In this case MME may also return a Control Plane data back-off timer within the NAS message.
The MME only includes the Control Plane data back-off timer if the UE has indicated support for Control Plane data back-off timer in the Attach/TAU/RAU request.
NOTE 3: If the MME is overloaded or close to overload, but the UE has not indicated support for Control Plane data back-off timer, the MME can use other overload control mechanisms, e.g. mobility management back-off timer or use user plane data communication.
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23.401
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4.3.7.5 PDN GW control of overload
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The PDN GW may provide mechanisms for avoiding and handling overload situations. These include the rejection of PDN connection requests from UEs.
The PDN GW may detect APN congestion and start and stop performing overload control based on criteria such as:
- Maximum number of active bearers per APN; and/or
- Maximum rate of bearer activations per APN.
When performing overload control the PDN GW rejects PDN connection requests. When receiving the rejection from the PDN GW, the MME rejects the UE's PDN connection request as specified in clause 4.3.7.4.2. In addition the PDN GW may indicate a "PDN GW back-off time" for a specific APN to the MME. The MME should reject PDN connection requests, for the specific APN related to that PDN GW during the "PDN GW back-off time", by the means specified in clause 4.3.7.4.2. If a PDN GW indicates APN congestion by the "PDN GW back-off time" the MME may select another PDN GW of that APN instead of rejecting PDN connection requests unless there is already an existing PDN connection to the same APN for the UE, in which case, the MME shall reject PDN connection request.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.8 Selection functions
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.8.1 PDN GW selection function (3GPP accesses)
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The PDN GW selection function allocates a PDN GW that shall provide the PDN connectivity for the 3GPP access. The function uses subscriber information provided by the HSS and possibly additional criteria such as SIPTO/LIPA support per APN configured in the SGSN/MME, UE support for dual connectivity with NR, 15 EPS bearers support by the UE, CIoT EPS Optimisation(s) impacting PDN GW e.g. Non-IP support, Ethernet support, NB-IoT RAT support (for generation of accounting information), etc.
NOTE 1: Selection of PDN GWs optimised for different RATs (e.g. NB-IoT) can be achieved by the allocation of different APNs to subscribers allowed to use specific RATs and/or using the UE Usage Type.
The criteria for PDN GW selection may include load balancing between PDN GWs. When the PDN GW IP addresses returned from the DNS server include Weight Factors, the MME should use it if load balancing is required. The Weight Factor is typically set according to the capacity of a PDN GW node relative to other PDN GW nodes serving the same APN. For further details on the DNS procedure see TS 29.303 [61].
When the MME supports the GTP-C Load Control feature, it takes into account the Load Information received from the PDN GW in addition to the Weight Factors received from the DNS server to perform selection of an appropriate PDN GW.
NOTE 2: How Weight Factors can be used in conjunction with Load Information received via GTP control plane signalling is left up to Stage 3.
The PDN subscription contexts provided by the HSS contain:
- the identity of a PDN GW and an APN (PDN subscription contexts with subscribed PDN GW address are not used when there is interoperation with pre Rel‑8 2G/3G SGSN), or
- an APN and an indication for this APN whether the allocation of a PDN GW from the visited PLMN is allowed or whether a PDN GW from the home PLMN shall be allocated. Optionally an identity of a PDN GW may be contained for handover with non-3GPP accesses.
- optionally for an APN, an indication of whether SIPTO above RAN, or SIPTO at the Local Network, or both, is allowed or prohibited for this APN.
- optionally for an APN, an indication of whether LIPA is conditional, prohibited, or only LIPA is supported for this APN.
In the case of static address allocation, a static PDN GW is selected by either having the APN configured to map to a given PDN GW, or the PDN GW identity provided by the HSS indicates the static PDN GW.
The HSS also indicates which of the PDN subscription contexts is the Default one for the UE.
To establish connectivity with a PDN when the UE is already connected to one or more PDNs, the UE provides the requested APN for the PDN GW selection function.
If one of the PDN subscription contexts provided by the HSS contains a wild card APN (see TS 23.003 [9]), a PDN connection with dynamic address allocation may be established towards any APN requested by the UE. An indication that SIPTO (above RAN, at the local network, or both) is allowed or prohibited for the wild card APN allows or prohibits SIPTO for any APN that is not present in the subscription data.
If the HSS provides the identity of a statically allocated PDN GW, or the HSS provides the identity of a dynamically allocated PDN GW and the Request Type indicates "Handover", no further PDN GW selection functionality is performed. If the HSS provides the identity of a dynamically allocated PDN GW, the HSS also provides information that identifies the PLMN in which the PDN GW is located.
NOTE 3: The MME uses this information to determine an appropriate APN-OI and S8 protocol type (PMIP or GTP) when the MME and PDN GW are located in different PLMNs.
If the HSS provides the identity of a dynamically allocated PDN GW and the Request Type indicates "initial Request", either the provided PDN GW is used or a new PDN GW is selected. When a PDN connection for an APN with SIPTO-allowed is requested, the PDN GW selection function shall ensure the selection of a PDN GW that is appropriate for the UE's location. The PDN GW identity refers to a specific PDN GW. If the PDN GW identity includes the IP address of the PDN GW, that IP address shall be used as the PDN GW IP address; otherwise the PDN GW identity includes an FQDN which is used to derive the PDN GW IP address by using Domain Name Service function, taking into account the protocol type on S5/S8 (PMIP or GTP).
NOTE 4: Provision of a PDN GW identity of a PDN GW as part of the subscriber information allows also for a PDN GW allocation by HSS.
If the HSS provides a PDN subscription context that allows for allocation of a PDN GW from the visited PLMN for this APN and, optionally, the MME is configured to know that the visited VPLMN has a suitable roaming agreement with the HPLMN of the UE, the PDN GW selection function derives a PDN GW identity from the visited PLMN. If a visited PDN GW identity cannot be derived, or if the subscription does not allow for allocation of a PDN GW from the visited PLMN, then the APN is used to derive a PDN GW identity from the HPLMN. The PDN GW identity is derived from the APN, subscription data and additional information by using the Domain Name Service function. If the PDN GW identity is a logical name instead of an IP address, the PDN GW address is derived from the PDN GW identity, protocol type on S5/S8 (PMIP or GTP) by using the Domain Name Service function. The S8 protocol type (PMIP or GTP) is configured per HPLMN in MME/SGSN.
In order to select the appropriate PDN GW for SIPTO above RAN service, the PDN GW selection function uses the TAI (Tracking Area Identity), the serving eNodeB identifier, or TAI together with serving eNodeB identifier depending on the operator's deployment during the DNS interrogation as specified in TS 29.303 [61] to find the PDN GW identity. In roaming scenario PDN GW selection for SIPTO is only possible when a PDN GW in the visited PLMN is selected. Therefore in a roaming scenario with home routed traffic, PDN GW selection for SIPTO is not performed.
In order to select the appropriate GW for SIPTO at the local network service with a stand-alone GW (with S-GW and L-GW collocated), the PDN GW selection function uses the APN and the Local Home Network ID during the DNS interrogation as specified in TS 29.303 [61] to find the PDN GW identity. The Local Home Network ID is provided to the MME by the (H)eNB in every INITIAL UE MESSAGE and every UPLINK NAS TRANSPORT control message as specified in TS 36.413 [36]. The MME uses the Local Home Network ID to determine if the UE has left its current local network and if S-GW relocation is needed.
For SIPTO at the Local Network with L-GW function collocated with the (H)eNB the PDN GW selection function uses the L-GW address proposed by the (H)eNB in the S1-AP message, instead of DNS interrogation.
In order to select the appropriate L-GW for LIPA service, if permitted by the CSG subscription data and if the UE is roaming, the VPLMN LIPA is allowed, the PDN GW selection function uses the L-GW address proposed by HeNB in the S1-AP message, instead of DNS interrogation. If no L-GW address is proposed by the HeNB and the UE requested an APN with LIPA permissions set to "LIPA-only", the request shall be rejected. If no L-GW address is proposed by the HeNB and the UE requested an APN with LIPA permissions set to "LIPA-conditional", the MME uses DNS interrogation for PDN GW selection to establish a non-LIPA PDN connection. The PDN subscription context for an APN with LIPA permissions set to "LIPA-only" shall not contain a statically configured PDN address or a statically allocated PDN GW. A static PDN address or a static PDN GW address, if configured by HSS for an APN with LIPA permissions set to "LIPA-conditional", is ignored by MME when the APN is established as a LIPA PDN connection. When establishing a PDN connection for a LIPA APN, the VPLMN Address Allowed flag is not considered.
The PDN GW domain name shall be constructed and resolved by the method described in TS 29.303 [61], which takes into account any value received in the APN‑OI Replacement field for non-roaming or home routed traffic. Otherwise, or when the resolution of the above PDN GW domain name fails, the PDN GW domain name shall be constructed by the serving node using the method specified in Annex A of TS 23.060 [7] and clause 9 of TS 23.003 [9]. If the Domain Name Service function provides a list of PDN GW addresses, one PDN GW address is selected from this list. If the selected PDN GW cannot be used, e.g. due to an error, then another PDN GW is selected from the list. The specific interaction between the MME/SGSN and the Domain Name Service function may include functionality to allow for the retrieval or provision of additional information regarding the PDN GW capabilities (e.g. whether the PDN GW supports PMIP‑based or GTP-based S5/S8, or both).
NOTE 5: The APN as constructed by the MME/SGSN for PDN GW resolution takes into account the APN-OI Replacement field. This differs from the APN that is provided in charging data to another SGSN and MME over the S3, S10 and S16 interfaces as well as to Serving GW and PDN GW over the S11, S4 and S5/S8 interfaces, in that the APN-OI Replacement field is not applied. See clause 5.7.2 of the present document for more details.
If the UE provides an APN for a PDN, this APN is then used to derive the PDN GW identity as specified for the case of HSS provided APN if one of the subscription contexts allows for this APN.
If there is an existing PDN connection to the same APN used to derive the PDN GW address, the same PDN GW shall be selected.
As part of PDN GW selection, an IP address of the assigned PDN GW may be provided to the UE for use with host based mobility as defined in TS 23.402 [2], if the PDN GW supports host-based mobility for inter-access mobility towards accesses where host-based mobility can be used. If a UE explicitly requests the address of the PDN GW and the PDN GW supports host based mobility then the PDN GW address shall be returned to the UE.
When DCNs with dedicated PDN GWs are used, the DNS procedure (TS 29.303 [61]) for PDN GW selection may be used such that a PDN GW belonging to a DCN serving a particular category of UEs, e.g. identified by UE Usage Type, is selected. When UEs with the same UE Usage type are served by multiple DCNs, it shall also be possible to select the PDN GW belonging to the DCN serving the particular UE.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.8.2 Serving GW selection function
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The Serving GW selection function selects an available Serving GW to serve a UE. The selection bases on network topology, i.e. the selected Serving GW serves the UE's location and for overlapping Serving GW service areas, the selection may prefer Serving GWs with service areas that reduce the probability of changing the Serving GW. When SIPTO is allowed then it is also considered as a criterion for Serving GW selection, e.g. when the first PDN connection is requested. Other criteria for Serving GW selection should include load balancing between Serving GWs, UE support for dual connectivity with NR, CIoT EPS Optimisation(s) impacting Serving GW e.g. Non-IP support, Ethernet support, NB-IoT RAT support (for generation of accounting information), etc. When the Serving GW IP addresses returned from the DNS server include Weight Factors, the MME should use it if load balancing is required. The Weight Factor is typically set according to the capacity of a Serving GW node relative to other Serving GW nodes serving the same Tracking area. For further details on DNS procedure see TS 29.303 [61].
When the MME supports the GTP-C Load Control feature, it takes into account the Load Information received from the Serving GW in addition to the Weight Factors received from the DNS server to perform selection of an appropriate Serving GW.
NOTE 1: How Weight Factors can be used in conjunction with Load Information received via GTP control plane signalling is left up to Stage 3.
If a subscriber of a GTP only network roams into a PMIP network, the PDN GWs selected for local breakout support the PMIP protocol, while PDN GWs for home routed traffic use GTP. This means the Serving GW selected for such subscribers may need to support both GTP and PMIP, so that it is possible to set up both local breakout and home routed sessions for these subscribers. For a Serving GW supporting both GTP and PMIP, the MME/SGSN should indicate the Serving GW which protocol should be used over S5/S8 interface. The MME/SGSN is configured with the S8 variant(s) on a per HPLMN granularity.
If a subscriber of a GTP only network roams into a PMIP network, the PDN GWs selected for local breakout may support GTP or the subscriber may not be allowed to use PDN GWs of the visited network. In both cases a GTP only based Serving GW may be selected. These cases are considered as roaming between GTP based operators.
If combined Serving and PDN GWs are configured in the network the Serving GW Selection Function may preferably derive a Serving GW that is also a PDN GW for the UE.
In order to provide SIPTO at the local network service with stand-alone GW, the L-GW and Serving GW shall be co-located. The Serving GW selection function in the MME is used to ensure that the Serving GW is provided according to operator policy as described in clause 4.3.15a. When the L-GW is collocated with the (H)eNB, the Serving GW remains located in the mobile operator's core network.
The Domain Name Service function may be used to resolve a DNS string into a list of possible Serving GW addresses which serve the UE's location. The specific interaction between the MME/SGSN and the Domain Name Service function may include functionality to allow for the retrieval or provision of additional information regarding the Serving GW capabilities (e.g. whether the Serving GW supports PMIP-based or GTP-based S5/S8, or both). The details of the selection are implementation specific.
For handover from non-3GPP accesses in roaming scenario, the Serving GW selection function for local anchoring is described in TS 23.402 [2].
The Serving GW selection function in the MME is used to ensure that all Tracking Areas in the Tracking Area List belong to the same Serving GW service area.
When DCNs with dedicated Serving GWs are used, the DNS procedure (TS 29.303 [61]) for Serving GW selection may be used such that a Serving GW belonging to a DCN serving a particular category of UEs, e.g. identified by UE Usage Type, is selected. When UEs with the same UE Usage type are served by multiple DCNs, it shall also be possible to select the Serving GW belonging to the DCN serving the particular UE.
NOTE 2: Selection of Serving GWs optimised for different RATs (e.g. NB-IoT) can be achieved by using UE Usage Type and/or by using different TAIs for different RATs.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.8.3 MME selection function
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The MME selection function selects an available MME for serving a UE. The selection is based on network topology, i.e. the selected MME serves the UE's location and for overlapping MME service areas, the selection may prefer MMEs with service areas that reduce the probability of changing the MME. When a MME/SGSN selects a target MME, the selection function performs a simple load balancing between the possible target MMEs. In networks that deploy dedicated MMEs/SGSNs for UEs configured for low access priority, the possible target MME selected by source MME/SGSN is typically restricted to MMEs with the same dedication.
When a MME/SGSN supporting DCNs selects a target MME, the selected target MME should be restricted to MMEs that belong to the same DCN. The DNS procedure may be used by the source CN node to select the target MME from a given DCN. If both low access priority and UE Usage Type parameter are used for MME selection, selection based on UE Usage type parameter overrides selection based on the low access priority indication.
When a MME supporting CIoT EPS Optimisation(s) selects a target MME, the selected MME should all support the CIoT EPS Optimisations applicable to the given UE's attachment. if the source MME is unable to find a target MME matching all CIoT EPS Optimisation(s) applicable to a given UE's attachment, then the source MME, based on implementation, selects a target MME which provides the CIoT EPS Optimisation(s) best applicable to that UE's attachment.
When an eNodeB selects an MME, the eNodeB may use a selection function which distinguishes if the GUMMEI is mapped from P-TMSI/RAI or is a native GUMMEI. The indication of mapped or native GUMMEI shall be signalled by the UE to the eNodeB as an explicit indication. The eNodeB may differentiate between a GUMMEI mapped from P‑TMSI/RAI and a native GUMMEI based on the indication signalled by the UE. Alternatively, the differentiation between a GUMMEI mapped from P-TMSI/RAI and a native GUMMEI may be performed based on the value of most significant bit of the MME Group ID, for PLMNs that deploy such mechanism. In this case, if the MSB is set to "0" then the GUMMEI is mapped from P-TMSI/RAI and if MSB is set to "1", the GUMMEI is a native one. Alternatively the eNodeB makes the selection of MME only based on the GUMMEI without distinguishing on mapped or native.
When an eNodeB selects an MME, the selection shall achieve load balancing as specified in clause 4.3.7.2.
When an eNodeB selects an MME, the selection shall consider the IAB support capability if the UE includes an IAB-Indication in the RRC connection establishment signalling as defined in TS 36.331 [37].
When the UE attempts to establish a signalling connection and the following conditions are met:
- the eNodeB serves more than one country (e.g. it supports E-UTRA satellite access); and
- the eNodeB knows in what country the UE is located; and
- the eNodeB is connected to MMEs serving different PLMNs of different countries; and
- the UE provides an S-TMSI or GUMMEI, which indicates an MME serving a different country to where the UE is currently located; and
- the eNodeB is configured to enforce selection of the MME based on the country the UE is currently located;
then the eNodeB shall select an MME serving a PLMN corresponding to the UE's current location. How the eNodeB selects the MME in this case is defined in TS 36.410 [92].
NOTE: When the UE accesses an eNodeB onboard a satellite (i.e. regenerative based satellite access), the eNodeB can be configured to select an MME supporting S1 Removal procedure defined in TS 36.413 [36].
When a satellite is operating in S&F Mode, the eNodeB is configured to enforce selection of the on-board MME supporting S&F Mode for every UE that accesses it.
When DCNs are deployed, to maintain a UE in the same DCN when the UE enters a new MME pool area, the eNodeB's NNSF should have configuration that selects, based on the MMEGIs or NRIs of neighbouring pool areas, a connected MME from the same DCN. Alternately, for PLMN wide inter-pool intra-RAT mobility, the operator may divide up the entire MMEGI and NRI value space into non-overlapping sets with each set allocated to a particular DCN. In this case all eNodeBs may be configured with the same MME selection configuration. If UE assisted DCN selection feature is supported and a DCN-ID is provided by the UE, the DCN-ID shall be used in the eNodeB for MME selection to maintain the same DCN when the serving MME is not available.
When selecting an MME for a UE that is using the NB-IoT RAT, and/or for a UE that signals support for CIoT EPS Optimisations in RRC signalling (as specified in TS 36.331 [37], for NB-IoT, UE indicates whether it supports "User Plane CIoT EPS Optimisation" and "EPS Attach without PDN Connectivity". And for WB-E-UTRAN, UE indicates whether it supports "Control Plane CIoT EPS Optimisation", "User Plane CIoT EPS Optimisation" and "EPS Attach without PDN Connectivity"), the eNodeB's MME selection algorithm shall select an MME taking into account the MME's support (or non-support) for the Release 13 NAS signalling protocol.
When DCN are deployed for the purpose of CIoT EPS Optimisation, UE included CIoT EPS Optimisation information in the RRC signalling, may depending on eNodeB configuration, be used to perform initial DCN selection.
When Restricted Local Operator Services feature is supported, a UE initiates access to Restricted Local Operator Services via RRC signalling as defined in TS 36.331 [37]. The UE included RLOS indication in RRC signalling may be used by the eNodeB to select an appropriate MME.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.8.4 SGSN selection function
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The SGSN selection function selects an available SGSN to serve a UE. The selection is based on network topology, i.e. the selected SGSN serves the UE's location and for overlapping SGSN service areas, the selection may prefer SGSNs with service areas that reduce the probability of changing the SGSN. When a MME/SGSN selects a target SGSN, the selection function performs a simple load balancing between the possible target SGSNs. In networks that deploy dedicated MMEs/SGSNs for UEs configured for low access priority, the possible target SGSN selected by source MME/SGSN is typically restricted to SGSNs with the same dedication.
When a MME/SGSN supporting DCNs selects a target SGSN, the selected target SGSN should be restricted to SGSNs that belong to the same CN. The DNS procedure may be used by the source CN node to select the target SGSN from a given DCN. If both low access priority and UE Usage Type parameter are used for SGSN selection, selection based on UE Usage type parameter overrides selection based on the low access priority indication.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.8.5 Selection of PCRF
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The PDN GW and AF may be served by one or more PCRF nodes in the HPLMN and, in roaming with local breakout scenarios, one or more PCRF nodes in the VPLMN.
The selection of PCRF and linking of the different UE's PCC sessions over the multiple PCRF interfaces (e.g. Rx session, Gx session, S9 session etc.) for a UE IP CAN session is described in TS 23.203 [6].
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.9 IP network related functions
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.9.1 Domain Name Service function
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The Domain Name Service function resolves logical PDN GW names to PDN GW addresses. This function is standard Internet functionality according to RFC 1034 [17], which allows resolution of any name to an IP address (or addresses) for PDN GWs and other nodes within the EPS.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.9.2 DHCP function
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The Dynamic Host Configuration Function allows to deliver IP configuration information for UEs. This function is standard Internet functionality according to RFC 2131 [19], RFC 8415 [94] and RFC 4039 [25].
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.9.3 Explicit Congestion Notification
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The E‑UTRAN/UTRAN and the UE support the RFC 3168 [55] Explicit Congestion Notification (ECN), as described in TS 36.300 [5], TS 25.401 [16] and TS 26.114 [56].
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.10 Functionality for Connection of eNodeBs to Multiple MMEs
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An eNodeB may connect to several MMEs. This implies that an eNodeB must be able to determine which of the MMEs, covering the area where an UE is located, should receive the signalling sent from a UE. To avoid unnecessary signalling in the core network, a UE that has attached to one MME should generally continue to be served by this MME as long as the UE is in the radio coverage of the pool area to which the MME is associated. The concept of pool area is a RAN based definition that comprises one or more TA(s) that, from a RAN perspective, are served by a certain group of MMEs. This does not exclude that one or more of the MMEs in this group serve TAs outside the pool area. This group of MMEs is also referred to as an MME pool.
To enable the eNodeB to determine which MME to select when forwarding messages from an UE, this functionality defines a routing mechanism (and other related mechanism). A routing mechanism (and other related mechanism) is defined for the MMEs. The routing mechanism is required to find the correct old MME (from the multiple MMEs that are associated with a pool area). When a UE roams out of the pool area and into the area of one or more MMEs that do not know about the internal structure of the pool area where the UE roamed from, the new MME will send the Identification Request message or the Context Request message to the old MME using the GUTI. The routing mechanism in both the MMEs and the eNodeB utilises the fact that every MME that serves a pool area must have its own unique value range of the GUTI parameter within the pool area.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.11 E-UTRAN Sharing Function
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E‑UTRAN Sharing is an agreement between operators and shall be transparent to the user. This implies that an E‑UTRAN UE needs to be able to discriminate between core network operators available in a shared radio access network and that these operators can be handled in the same way as operators in non-shared networks. E‑UTRAN terminals support E‑UTRAN Sharing.
An E‑UTRAN Sharing architecture allows different core network operators to connect to a shared radio access network. The operators do not only share the radio network elements, but may also share the radio resources themselves. In addition to this shared radio access network the operators may or may not have additional dedicated radio access networks, like for example, 3G or 2G radio access networks. For E‑UTRAN both Multi-Operator Core Network (MOCN) configuration and Gateway Core Network (GWCN) configuration as defined in TS 23.251 [24] are supported over the S1 reference point. E‑UTRAN terminals shall support shared networks and hence, only functions for "Supporting UEs" in TS 23.251 [24] applies for E‑UTRAN Sharing.
E‑UTRAN Radio Access Network Sharing functions is further described in TS 36.300 [5].
In networks that support network sharing as defined in TS 23.251 [24], for a UE in state ECM-CONNECTED, the Handover Restriction List provided by the core-network to the radio access network is also used to inform the radio access network about the Selected PLMN and equivalent PLMNs as defined in TS 36.413 [36].
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.12 IMS Emergency Session Support
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.12.1 Introduction
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Clause 4.3.12 IMS Emergency Session provides an overview about functionality for emergency bearer services in a single clause. This overview applies to eCall Over IMS unless stated otherwise. The specific functionality is described in the affected procedures and functions of this specification. For discrepancies between this overview clause and the detailed procedure and function descriptions the latter take precedence.
Emergency bearer services are provided to support IMS emergency sessions. Emergency bearer services are functionalities provided by the serving network when the network is configured to support emergency services. Emergency bearer services are provided to normal attached or emergency attached UEs and depending on local regulation, to UEs that are in limited service state. Receiving emergency services in limited service state does not require a subscription. Depending on local regulation and an operator's policy, the MME may allow or reject an emergency attach request for UEs in limited service state. Four different behaviours of emergency bearer support have been identified as follows:
a. Valid UEs only. No limited service state UEs are supported in the network. Only UEs that have a valid subscription, are authenticated and authorized for PS service in the attached location are allowed. UEs should be attached to the network and then perform a PDN Connection Request when an IMS emergency session is detected by the UE.
b. Only UEs that are authenticated are allowed. These UEs must have a valid IMSI. These UEs are authenticated and may be in limited service state due to being in a location that they are restricted from service. A UE that can not be authenticated will be rejected.
c. IMSI required, authentication optional. These UEs must have an IMSI. If authentication fails, the UE is granted access and the unauthenticated IMSI retained in the network for recording purposes. The IMEI is used in the network as the UE identifier. IMEI only UEs will be rejected (e.g., UICCless UEs).
d. All UEs are allowed. Along with authenticated UEs, this includes UEs with an IMSI that can not be authenticated and UEs with only an IMEI. If an unauthenticated IMSI is provided by the UE, the unauthenticated IMSI is retained in the network for recording purposes. The IMEI is used in the network to identify the UE.
To provide emergency bearer services, the MME is configured with MME Emergency Configuration Data that are applied to all emergency bearer services that are established by an MME on UE request. The MME Emergency Configuration Data contain the Emergency APN which is used to derive a PDN GW, or the MME Emergency Configuration Data may also contain the statically configured PDN GW for the Emergency APN.
For Cellular IoT over satellite access, if a UE in limited service state is aware of its location within certain country, the UE should select a PLMN that serves the country where the UE is located as specified in clause 4.13.2. The network may be configured to verify the location of a UE that is registering for emergency services as specified in clause 4.13.4.
UEs that are in limited service state, as specified in TS 23.122 [10], initiate the Attach procedure with indicating that the attach is to receive emergency services. Also UEs that had attached for normal services and do not have emergency bearers established and are camped on a cell in limited service state (e.g. because of restricted Tracking Area or not allowed CSG) shall initiate this Attach procedure, indicating that the attach is to receive emergency services. The network supporting emergency services for UEs in limited service state provides emergency bearer services to these UE, regardless whether the UE can be authenticated, has roaming or mobility restrictions or a valid subscription, depending on local regulation. For emergency services other than eCall, the UEs in limited service state determine that the cell supports emergency services over E-UTRAN from a broadcast indicator in AS. Emergency calls for eCall Over IMS are only performed if the UE has a UICC.
A serving network shall provide an Access Stratum broadcast indication to UEs as to whether eCall Over IMS is supported.
NOTE 1: The Access Stratum broadcast indicator is determined according to operators' preference and minimally indicates that the PLMN, or all of the PLMNs in the case of network sharing, and at least one emergency centre or PSAP to which an eCall Over IMS session can be routed, support eCall Over IMS.
A UE in limited service state determines that the cell supports eCall Over IMS using both the broadcast indicator for support of emergency services over E-UTRAN and the broadcast indicator for eCall over IMS.
NOTE 2: The broadcast indicator for eCall Over IMS does not indicate whether UEs in limited service state are supported, as such the broadcast indicator for support of emergency services over E-UTRAN that indicates limited service state support needs to also be applied.
For a UE that is Emergency Attached, if it is unauthenticated the EPS security context is not set up on UE.
UEs that camp normally on a cell, i.e. without any conditions that result in limited service state, initiate the normal initial attach procedure if not already attached. Normal attached UEs initiate the UE Requested PDN Connectivity procedure to receive emergency bearer services. The UEs that camp normally on a cell are informed that the PLMN supports emergency bearer services over E-UTRAN from the Emergency Service Support indicator in the Attach and TAU procedures. MME may be configured to indicate Emergency Service Support indicator on a per-HPLMN basis. UEs that camp normally on a cell may also use the emergency attach procedure under conditions specified in TS 24.301 [46], e.g. when the MM back-off timer is running.
NOTE 3: Failure of the normal initial attach may occur e.g. when the network rejects the request with a back-off time.
NOTE 4: The establishment of the emergency bearer services may fail when the UE needs to perform a TAU prior to the UE Requested PDN Connectivity procedure, i.e. the UE moved into a non-registered Tracking Area with the MM back-off timer running in the UE.
NOTE 5: The Emergency Service Support indicator in the Attach and TAU procedures does not enable support for eCall Over IMS.
For a UE that is Emergency Attached, normal PLMN selection principles apply after the end of the IMS emergency session.
For emergency bearer services any EPC functions, procedures and capabilities are provided according to clause 4 except when specified differently in the following clauses.
For emergency bearer services, there is a risk of service disruption due to failed inter PLMN mobility attempts.
For emergency bearer services, handover from non-3GPP access to E-UTRAN access is supported as specified in TS 23.402 [2] clause 4.5.7.2.10.
The UE shall set the RRC establishment cause or RRC resume cause to emergency as defined in TS 36.331 [37] when it requests an RRC connection in relation to an emergency session. Specific situations that require setting the RRC establishment cause or RRC resume cause to emergency are described in TS 24.301 [46].
Support for emergency bearer services is not available when the UE is using NB-IoT, i.e. the MME shall not indicate support for emergency bearer services using the Emergency Service Support indicator in the Attach and TAU procedures to a UE that accesses the network using a RAT Type equal to NB-IoT, and an NB-IoT cell shall not indicate support for emergency services in any broadcast information in AS.
When a PLMN supports IMS and emergency bearer services, all MMEs in that PLMN shall have the same capability to support emergency bearer services.
NOTE 6: Idle mode Signalling Reduction (ISR) is not supported by the network for UEs that only have bearers related to emergency bearer service.
For emergency services other than eCall, a UE that is not in in limited service state, as specified in TS 23.122 [10] determines from a NAS indicator whether additional emergency numbers/types received via WLAN from trusted sources may be used for detecting emergency calls.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.12.2 Architecture Reference Model for Emergency Services
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According to clause 4.2, the non-roaming architectures (Figure 4.2.1-1 and Figure 4.2.1-2) and roaming architecture with the visited operator's application function (Figure 4.2.2-3) apply for emergency services. The other roaming architectures with services provided by the home network do not apply for emergency services.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.12.3 Mobility and Access Restrictions for Emergency Services
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When Emergency Services are supported and local regulation requires Emergency Sessions to be provided regardless of mobility or access restrictions, the Mobility Restrictions in clause 4.3.5.7, should not be applied to UEs receiving emergency services. When the E-RABs for emergency bearers are established, the ARP value for emergency bearer services indicates the usage for emergency services to the E-UTRAN.
During handovers, the source E-UTRAN and source MME ignore any UE related restrictions during handover evaluation when there are active emergency bearers. E‑UTRAN shall not initiate handover to GERAN PS domain. During handover to a CSG cell, if the UE is not a CSG member of target CSG cell and has emergency bearer services, the target eNodeB only accepts the emergency bearers and the target MME releases the non-emergency PDN connections that were not accepted by the target eNodeB as specified in clause 5.10.3. Such UEs behave as emergency attached.
During Tracking Area Update procedures, including a TAU as part of a handover, the target MME ignores any mobility or access restrictions for UE with emergency bearer services where required by local regulation. Any non-emergency bearer services are deactivated, according to clause 5.10.3, by the target MME when not allowed by the subscription for the target location. Such UEs behave as emergency attached. To allow the emergency attached UE to get access to normal services after the emergency session has ended and when it has moved to a new area that is not stored by the UE as a forbidden area, the UE may explicitly detach and reattach to normal services without waiting for the emergency PDN connection deactivation by the PDN GW.
This functionality applies to all mobility procedures.
4.3.12.3a Reachability Management for UE in ECM-IDLE state
An emergency attached UE when its periodic TAU update timer expires shall not initiate a periodic TAU procedure but enter EMM-DEREGISTERED state. For emergency attached UEs the MME runs a mobile reachable timer with a similar value to the UE's periodic TAU timer. Any time after expiry of this timer the MME may change the EMM state of an emergency attached UE to EMM-DEREGISTERED. The MME assigns the periodic TAU timer value to emergency attached UE. This timer keeps the UE emergency attached after change to EMM-IDLE state to allow for a subsequent emergency service without a need to emergency attach again.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.12.4 PDN GW selection function (3GPP accesses) for Emergency Services
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When a PDN GW is selected for IMS emergency services support, the PDN GW selection function described in clause 4.3.8.1 for normal bearer services is applied to the Emergency APN or the MME selects the PDN GW directly from the MME Emergency Configuration Data. If the PDN GW selection function described in clause 4.3.8.1 is used it shall always derive a PDN GW in the visited PLMN, which guarantees that also the IP address is allocated by the visited PLMN. In networks that support handover between E‑UTRAN and HRPD accesses, the MME selects a PDN GW that is statically configured in the MME Emergency Configuration Data. In networks that support handover between E‑UTRAN and WLAN accesses, when the UE has been authorized but has not been authenticated, the MME selects the PDN GW that is statically configured in the MME Emergency Configuration Data. The PDN GW selection does not depend on subscriber information in the HSS since emergency service support is a local, not subscribed service. The MME Emergency Configuration Data contains the Emergency APN which is used to derive a PDN GW, or the MME Emergency Configuration Data may also contain the statically configured PDN GW for the Emergency APN. In the case of GateWay Core Network sharing, the MME shall support separate MME Emergency Configuration Data for each of the sharing PLMNs. In the case of GateWay Core Network sharing and PDN GW selection for the Emergency APN, the MME shall be able to take the selected PLMN ID into account to derive a PDN GW.
This functionality is used by the Attach procedure and by the UE Requested PDN Connectivity procedure, in both cases when establishing emergency bearer services.
NOTE: It is assumed that the PDN GW that is statically configured in the MME Emergency Configuration Data is the same as the PDN GW configured in WLAN and HRPD accesses.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.12.5 QoS for Emergency Services
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Where local regulation require supporting calls from an unauthorised caller, the MME may not have subscription data. Additionally, the local network may want to provide IMS emergency services support differently than what is allowed by a UE subscription. Therefore, the initial QoS values used for establishing emergency bearer services are configured in the MME in the MME Emergency Configuration Data.
NOTE: For IMS emergency services prior to this Release of this specification, dynamic PCC support was not required in the specifications. In such cases, the PDN GW sets the ARP value that is reserved for emergency services, which the PDN GW bases on the usage of the Emergency APN.
This functionality is used by the Attach procedure and by the UE Requested PDN Connectivity procedure, in both cases when establishing emergency bearer services.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.12.6 PCC for Emergency Services
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Dynamic PCC is used for UEs establishing emergency service, the procedures are as described in TS 23.203 [6]. When establishing emergency bearer services with a PDN GW, according to clause 4.7.5, the PCRF provides the PDN GW with the QoS parameters, including an ARP value reserved for the emergency bearers to prioritize the bearers when performing admission control. Dynamic PCC shall be used to manage IMS emergency sessions when an operator allows IMS emergency sessions.
NOTE: For IMS emergency services prior to this Release of this specification, dynamic PCC support was not required in the specifications. According to clause 4.7.5, when solely using voice/GTT, local configuration of static policy functions is also allowed prior to this Release of this specification and is not subject to standardization.
The PCRF ensures that the emergency PDN connection is used only for IMS emergency sessions. The PCRF rejects an IMS session established via the emergency PDN connection if the AF (i.e. P-CSCF) does not provide an emergency indication to the PCRF.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.12.7 Load re-balancing between MMEs for Emergency Services
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As per load re-balancing procedures in clause 4.3.7.3, the MME is allowed to off-load ECM-CONNECTED mode UEs by initiating S1 Release procedures. When a UE is in ECM-CONNECTED mode with an active emergency bearer service, the MME should not release the UE for load re-balancing. The MME should wait until the UE initiates a TAU or becomes inactive. The MME may release the UE under critical conditions such as the need to perform an MME node restart.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.12.8 IP Address Allocation
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Emergency bearer service is provided by the serving PLMN. The UE and PLMN must have compatible IP address versions in order for the UE to obtain a local emergency PDN connection. IP address allocation in the serving PLMN is provided per clause 5.3.1 with the exception that the PDN GW associated with the emergency APN shall support PDN type IPv4 and PDN type IPv6.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.12.9 Handling of PDN Connections for Emergency Bearer Services
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The default and dedicated EPS bearers of a PDN Connection associated with the emergency APN shall be dedicated for IMS emergency sessions and shall not allow any other type of traffic. The emergency bearer contexts shall not be changed to non-emergency bearer contexts and vice versa. The PDN GW shall block any traffic that is not from or to addresses of network entities (e.g. P-CSCF) providing IMS emergency service. Dynamic PCC shall be deployed in order to support IMS emergency sessions, the procedures are as described in TS 23.203 [6]. If there is already an emergency PDN GW connection, the UE shall not request another emergency PDN Connection. The MME shall reject any additional emergency PDN Connection requests. The UE shall not request any bearer resource modification for the emergency PDN connection. The PDN GW shall reject any UE requested bearer resource modification that is for the emergency PDN Connection. The ARP reserved for emergency bearer service shall only be assigned to EPS bearers associated with an emergency PDN Connection.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.12.10 ISR function for Emergency Bearer Services
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When UE has only emergency bearer service, ISR does not apply.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.12.11 Support of eCall Only Mode
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For service requirements for eCall only mode, refer to TS 22.101 [80].
A UE configured for eCall Only Mode shall remain in EMM-DEREGISTERED state, shall camp on a network cell when available but shall refrain from any Mobility Management or other signalling with the network. The UE may instigate Mobility Management and Connection Management procedures in order to establish, maintain and release an eCall Over IMS session or a session to any non-emergency MSISDN(s) or URI(s) configured in the UICC for test and/or terminal reconfiguration services. Following the release of either session, the UE starts a timer whose value depends on the type of session (i.e. whether eCall or a session to a non-emergency MSISDN or URI for test/reconfiguration). While the timer is running, the UE shall perform normal Mobility Management procedures and is permitted to respond to paging to accept and establish an incoming session (e.g. from an emergency centre, PSAP or HPLMN operator). When the timer expires, the UE shall perform a UE-initiated detach procedure if still attached and enter EMM-DEREGISTERED state.
NOTE 1: An HPLMN operator can change the eCall Only Mode configuration state of a UE in the UICC. An HPLMN operator can also instead add, modify or remove a non-emergency MSISDN or URI in the UICC for test and/or terminal reconfiguration services. This can occur following a UE call to a non-emergency MSISDN or URI configured for reconfiguration. When the eCall Only Mode configuration is removed, the UE operates as a normal UE that can support eCall over IMS.
NOTE 2: A test call and a reconfiguration call can be seen as normal (non-emergency) call by a serving PLMN and normal charging rules can apply depending on operator policy.
NOTE 3: An MSISDN configured in the UICC for test and/or terminal reconfiguration services for eCall Over IMS can differ from an MSISDN configured in the UICC for test services for eCall over the CS domain.
When attaching to EPS for E-UTRAN access, a UE configured for eCall Only Mode may indicate support for radio capabilities for IRAT Handover (for UTRAN) or SRVCC Handover (for GERAN), but shall not indicate support for IMS Voice over RATs other than E-UTRAN.
NOTE 4: Access to the PS domain for a UE configured for eCall Only Mode is only supported by E-UTRAN in this version of the specification.
4.3.12a Support of Restricted Local Operator Service
4.3.12a.1 Introduction
Restricted Local Operator Services is an optional feature supported in certain countries. Service requirements of Restricted Local Operator Services is defined in TS 22.101 [80] and the architectural requirements are defined in TS 23.221 [27].
Access to Restricted Local Operator Services may be allowed for UEs in limited service state by the serving network depending on local regulation and operator policies. UEs may enter limited service state as specified in clause 4.3.12.1.
RLOS is requested by the UE, based on explicit request from the user. When attaching to the network to access RLOS, the UE shall send a NAS RLOS indication to the MME, which proceeds with the RLOS attach procedure described in clause 5.3.2.1 A specific RLOS-APN, unique for the PLMN, is configured in the MME.
Allowing access to RLOS is completely under the local operator's control, e.g. EPC access for RLOS does not depend on whether the UE is authenticated or not, nor on whether authentication succeeds or fails.
To provide access to Restricted Local Operator Services, the MME is configured with MME RLOS Configuration Data that are applied to RLOS PDN connection that is established by an MME upon UE request. The MME RLOS Configuration Data contain the RLOS APN which is used to derive a PDN GW, or the MME RLOS Configuration Data may contain the statically configured PDN GW for the RLOS APN.
UEs in limited service state intending to access Restricted Local Operator Services determines that the cell supports RLOS services over E-UTRAN via a broadcast indicator in AS and subsequently initiates the Attach procedure with an indication that the attach is to access RLOS. The Networks supporting Restricted Local Operator Services provides access to these UEs, regardless whether authentication for the UEs is performed or not, and regardless of the authentication result if authentication is performed. If the PLMN does not advertise its support of RLOS, the UE shall block the origination attempt for RLOS.
Restricted Local Operator Services is applicable to WB-E-UTRAN only. Restricted Local Operator Services does not support UE requested PDN connectivity, inter-RAT mobility and Network triggered Service Request. Handover between 3GPP and non-3GPP accesses are not supported for UEs attached for RLOS. Location service does not apply to Restricted Local Operator Services.
NOTE 1: During situations when, for example, there is lack of resource in E-UTRAN, the E-UTRAN node can set the broadcast indicator accordingly in order to indicate that the RLOS UEs in the cell are not allowed.
NOTE 2: The RAN can take into account that the UE is attached for access to RLOS when setting the UE inactivity timer to avoid unnecessary release of the RRC connection in situations where the network response takes time to arrive.
On-line charging is not activated for RLOS APN. For off-line charging, an RLOS APN indication as well as IMEI, if available, is added to charging records.
4.3.12a.2 Architecture Reference Model for Restricted Local Operator Services
The same architecture as for emergency service specified in clause 4.3.12.2 applies.
4.3.12a.3 Mobility and Access Restrictions
When access to Restricted Local Operator Services is supported, the Mobility Restrictions in clause 4.3.5.7 should not be applied to UEs receiving Restricted Local Operator Services. However, for a RLOS attached UE, the MME shall restrict mobility to GERAN and UTRAN, and include GERAN and UTRAN in the Handover Restriction List.
4.3.12a.4 PDN GW selection function for Restricted Local Operator Services
Same mechanism as for emergency service specified in clause 4.3.12.4 applies with the following difference:
For Restricted Local Operator Services, RLOS Configuration Data containing RLOS APN is needed in MME. However, HRPD or WLAN handovers don't apply.
4.3.12a.5 QoS for Restricted Local Operator Services
The initial QoS values used for establishing RLOS PDN connection during RLOS attach are obtained from the MME RLOS Configuration Data.
4.3.12a.6 PCC for Restricted Local Operator Services
Dynamic PCC based on the procedures described in TS 23.203 [6] may be used for UEs accessing Restricted Local Operator Services which involve voice services. When establishing PDN connection towards the RLOS APN with a PDN GW, according to clause 4.7.5, the PCRF provides the PDN GW with the QoS parameters, based on operator policy, including an ARP value reserved for the Restricted Local Operator Services where RLOS has a lower priority in terms of admission control than regular PDN connections
The PCRF ensures that the RLOS PDN connection is used only for Restricted Local Operator Services. The PCRF rejects an IMS session established via the RLOS PDN connection if the AF (i.e. P-CSCF) does not provide an RLOS indication to the PCRF.
4.3.12a.7 IP Address Allocation
RLOS is provided by the serving PLMN. The UE and PLMN must have compatible IP address versions in order for the UE to obtain a RLOS PDN connection. IP address allocation in the serving PLMN is provided according to clause 5.3.1 with the exception that the PDN GW associated with the RLOS APN shall support PDN type IPv4 and PDN type IPv6.
4.3.12a.8 Emergency service for RLOS attached UE
For an RLOS attached UE initiating emergency service, the UE shall first perform a local detach prior to initiating an emergency attach as described in TS 24.301 [46].
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23.401
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4.3.13 Closed Subscriber Group functions
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Closed Subscriber Group identifies a group of subscribers who are permitted to access one or more CSG cells of the PLMN as a member of the CSG for a HeNB. The following CSG related functions are defined:
- CSG subscription handling function stores and updates the user's CSG subscription data at the UE and the network.
- For closed mode, CSG access control function ensures a UE has valid subscription at a CSG where it performs an access.
- Admission and rate control function is used to provide different admission and rate control for CSG and non-CSG members for a hybrid CSG cell.
- CSG charging function enables per CSG charging for a subscriber consuming network services via a CSG cell or a hybrid cell.
- CSG Paging Optimisation function is optionally used to filter paging messages as described in clause 5.3.4.3.
- VPLMN Autonomous CSG roaming function is optionally supported whereby a VPLMN, if allowed by the HPLMN, stores and manages VPLMN specific CSG subscription information for roaming UEs without interaction with the HSS.
- CSG membership verification without updating the User CSG Information in the Core Network in the case of Dual Connectivity when the Secondary eNodeB is a hybrid access eNodeB.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.14 Location Service functions
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LCS procedures are described in the LCS stage 2 specification, see TS 23.271 [57].
In addition, in the Detach and Bearer Deactivation procedures, the MME shall inform the S-GW of the last known location of the UE, and shall provide information to enable the determination of the time at which the UE was in that location. The S-GW shall (if necessary taking into account information from the SGSN) inform the PDN GW of the last known location of the UE, and shall provide information to enable the determination of the time at which the UE was in that location. If requested by the PCRF the PDN GW shall indicate this information to the PCRF as defined in TS 23.203 [6]. The information can also be made available on the SGi interface as specified in TS 29.061 [38] and on the CDRs at network elements such as the S-GW and PDN GW as specified in TS 32.251 [44].
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.15 Selected IP Traffic Offload (SIPTO) function
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The SIPTO function enables an operator to offload certain types of traffic at a network node close to that UE's point of attachment to the access network. The SIPTO function specified in this TS applies to IP PDN Types and Ethernet and Non-IP PDN Types.
SIPTO above RAN can be achieved by selecting a set of GWs (S-GW and P-GW) that is geographically/topologically close to a UE's point of attachment.
SIPTO above RAN corresponds to a traffic offload through a P-GW located in the mobile operator's core network.
SIPTO applies to both the non-roaming case and, provided appropriate roaming agreements are in place between the operators, to the roaming case.
Offload of traffic for a UE is available for UTRAN and E-UTRAN accesses only. When the UE enters to UTRAN/E-UTRAN from another type of access network (e.g., from GERAN), it is the responsibility of the new SGSN/MME to decide whether to perform deactivation with reactivation request for a given PDN connection, depending on SIPTO permissions for the relevant APN.
Realization for SIPTO above RAN relies on the same architecture models and principles as for local breakout described in clause 4.2.
In order to select a set of appropriate GW (S-GW and P-GW) based on geographical/topological proximity to UE, the GW selection function specified in TS 29.303 [61] uses the UE's current location information.
In order for the operator to allow/prohibit SIPTO on per user and per APN basis, subscription data in the HSS is configured to indicate to the MME if offload is allowed or prohibited. If the SIPTO permissions information from the HSS conflicts with MME's configuration for that UE, then SIPTO is not used.
If HSS indicates VPLMN address not allowed, then VPLMN (i.e. MME) shall not provide SIPTO.
In the absence of any SIPTO permissions indication from the HSS the VPLMN (i.e MME) shall not provide SIPTO.
The MME may be configured on a per APN basis as to whether or not to use SIPTO (e.g. to handle the case where the HSS is not configured with SIPTO information for the UE).
For SIPTO above RAN, as a result of UE mobility (e.g. detected by the MME at TAU or SGSN at RAU or movement from GERAN), the target MME may wish to redirect a PDN connection towards a different GW that is more appropriate for the UE's current location, e.g. MME may know whether the UE's new location is served by the same GW as the old one. When the MME decides upon the need for GW relocation, the MME deactivates the impacted PDN connections indicating "reactivation requested" as specified in clause 5.10.3. If all of the PDN connections for the UE need to be relocated, the MME may initiate the "explicit detach with reattach required" procedure as specified in clause 5.3.8.3.
NOTE: If either of the above procedures for GW relocation are initiated while the UE has active applications, it may cause disruption of services that are affected if the IP address changes.
4.3.15a Selected IP Traffic Offload (SIPTO) at the Local Network
4.3.15a.1 General
The SIPTO at the Local Network function enables an IP capable UE connected via a (H)eNB to access a defined IP network (e.g. the Internet) without the user plane traversing the mobile operator's network.
The subscription data in the HSS are configured per user and per APN to indicate to the MME if offload at the local network is allowed or not.
SIPTO at the Local Network can be achieved by selecting a L-GW function collocated with the (H)eNB or selecting stand-alone GWs (with S-GW and L-GW collocated) residing in the Local Network. In both cases the selected IP traffic is offloaded via the Local Network.
Specific to the HeNB subsystem, the applicability of SIPTO at the Local Network does not depend on CSG membership and the feature can be applied to any UE, as long as the UE is allowed to access the cell.
For this release of the specification, no interface between the L-GW and the PCRF is specified and there is no support for dedicated bearers on the PDN connection used for SIPTO at the Local Network. The Local GW (L-GW) shall reject any UE requested bearer resource modification.
For this release of the specification, SIPTO at the Local Network is intended for offloading Internet traffic only, thus the L-GW does not provide APN specific connectivity. Therefore if the subscription data in the HSS indicate that offload at the Local Network is allowed, this implies that the related APN is typically used for providing Internet connectivity.
If the MME detects a change in SIPTO permissions in the subscription data for a given subscriber for a given APN and the subscriber has already established a SIPTO at the local network PDN connection to that APN, the MME shall release the SIPTO at the Local Network PDN connection for that APN with "reactivation requested" cause as specified in clause 5.10.3.
NOTE: In this release of the specification it is assumed that the target S-GW selected during the Handover also has connectivity to the L-GW.
4.3.15a.2 SIPTO at the Local Network with stand-alone GW (with S-GW and L-GW collocated) function
SIPTO at the Local Network is achieved using a stand-alone GW (with S-GW and L-GW collocated) residing in the Local Network.
A (H)eNB supporting SIPTO at the Local Network with the stand-alone GW includes the Local Home Network ID to the MME in every INITIAL UE MESSAGE, every UPLINK NAS TRANSPORT control message, HANDOVER NOTIFY and PATH SWITCH REQUEST messages.
If a SIPTO PDN connection is initiated as an additional subsequent PDN connection, the MME should check if the S‑GW is optimal for the user's current location. If it is not, and if the network supports S-GW relocation without being triggered by a mobility event, the MME may decide to perform an MME triggered Serving GW relocation according to clause 5.10.4, when possible (e.g. no other restrictions apply).
For SIPTO at the Local Network with a stand-alone GW, the location of the Serving GW may be determined based on the operator policy and user's profile regarding support of SIPTO at Local Network so that:
- At attachment to the (H)eNB, a local S-GW can always be selected independent of whether a SIPTO at the Local Network PDN connection is established or not. If mobility is performed to the macro network without having a SIPTO connection, a S-GW relocation can be performed as specified via existing mobility procedures with S-GW relocation.
- At attachment to a (H)eNB, a macro S-GW may be allocated for PDN connection in the operator's network. If a new PDN connection is requested by the UE that requires that a local S-GW is selected to provide for SIPTO at the Local Network, S-GW relocation from the macro S-GW to the local S-GW shall be performed as specified in clause 5.10.4.
As IP data session continuity for SIPTO at the Local Network PDN connection is not supported in this release of the specification, subsequent to handover completion the (target) MME should disconnect the SIPTO at the Local Network PDN connection with "reactivation requested" cause as specified in clause 5.10.3, unless the Local Home Network ID is not changed. The IP data session should be maintained if the Local Home Network ID is not changed. If the UE has no other PDN connection and the Local Home Network ID is changed, the (target) MME initiates "explicit detach with reattach required" procedure according to clause 5.3.8.3.
Upon completion of Tracking Area Update procedure, the (new) MME shall trigger the re-establishment of the SIPTO at the Local Network PDN connection when it detects that the UE has moved away from the (H)eNB and to a (H)eNB with different Local Home Network ID, as specified in clause 5.3.3 and clause 5.3.4.
NOTE: It is expected that all MMEs/SGSNs in a PLMN have support for SIPTO at the Local Network where the operator deploys this feature, in order to support mobility procedures. For a mobility event where target MME/SGSN does not support SIPTO at the Local Network, the handling of PDN deactivation for SIPTO at Local Network PDN connection is not specified.
4.3.15a.3 SIPTO at the Local Network with L-GW function collocated with the (H)eNB
SIPTO at the Local Network is achieved using a Local GW (L-GW) function collocated with the (H)eNB and using the same procedures as described in clause 4.3.15, with the following additions:
- The (H)eNB supporting the SIPTO at the Local Network function includes the Local GW address to the MME in every INITIAL UE MESSAGE and every UPLINK NAS TRANSPORT control message specified in TS 36.413 [36].
- The PDN GW selection function uses the L-GW address proposed by (H)eNB in the S1-AP message, instead of DNS interrogation.
- Specific to the HeNB subsystem, the Local GW information for SIPTO at the Local Network is signalled on S1 separately from the Local GW information for LIPA. The L-GW shall be able to discriminate between PDN connection for SIPTO at the Local Network and for LIPA.
NOTE 1: The protocol option (i.e. GTP or PMIP) supported on the S5 interface between Local GW and S‑GW is configured on the MME.
The direct user plane path between the (H)eNB and the collocated L-GW is enabled with a SIPTO Correlation ID parameter that is associated with the default EPS bearer on the PDN connection used for SIPTO at the Local Network. Upon establishment of the default EPS bearer the MME sets the SIPTO Correlation ID equal to the PDN GW TEID (GTP-based S5) or the PDN GW GRE key (PMIP-based S5). The SIPTO Correlation ID is then signalled by the MME to the (H)eNB as part of E-RAB establishment and is stored in the E-RAB context in the (H)eNB. The SIPTO Correlation ID is used in the (H)eNB for matching the radio bearers with the direct user plane path connections from the collocated L-GW for SIPTO at local network PDN connection.
As IP data session continuity for the SIPTO at the Local Network PDN connection is not supported in this release of the specification, the SIPTO at the Local Network PDN connection shall be re-established when the UE moves away from (H)eNB. During the handover procedure, when the source (H)eNB releases its resources related to the UE, the (H)eNB shall request using intra-node signalling the collocated L-GW to re-establish the SIPTO at the Local Network PDN connection. The L-GW starts a timer. When the timer expires, the L-GW shall initiate the release of the SIPTO at the Local Network PDN connection using the PDN GW initiated bearer deactivation procedure according to clause 5.4.4.1 with the "reactivation requested" cause value.
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4.3.16 Local IP Access (LIPA) function
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The LIPA function enables a UE connected via a HeNB to access other entities in the same residential/enterprise network without the user plane traversing the mobile operator's network except HeNB subsystem.
The Local IP Access is achieved using a Local GW (L-GW) collocated with the HeNB.
LIPA is established by the UE requesting a new PDN connection to an APN for which LIPA is permitted, and the network selecting the Local GW associated with the HeNB and enabling a direct user plane path between the Local GW and the HeNB. The HeNB supporting the LIPA function includes the Local GW address to the MME in every INITIAL UE MESSAGE and every UPLINK NAS TRANSPORT control message as specified in TS 36.413 [36].
NOTE 1: The protocol option (i.e. GTP or PMIP) supported on the S5 interface between Local GW and S‑GW is configured on the MME.
For this release of the specification no interface between the L-GW and the PCRF is specified and there is no support for Dedicated bearers on the PDN connection used for Local IP Access. The Local GW (L-GW) shall reject any UE requested bearer resource modification.
The direct user plane path between the HeNB and the collocated L-GW is enabled with a Correlation ID parameter that is associated with the default EPS bearer on a PDN connection used for Local IP Access. Upon establishment of the default EPS bearer the MME sets the Correlation ID equal to the PDN GW TEID (GTP-based S5) or the PDN GW GRE key (PMIP-based S5). The Correlation ID is then signalled by the MME to the HeNB as part of E-RAB establishment and is stored in the E-RAB context in the HeNB. The Correlation ID is used in the HeNB for matching the radio bearers with the direct user plane path connections from the collocated L-GW.
If the UE is roaming and if the HSS indicates LIPA roaming allowed for this UE in this VPLMN, then the VPLMN (i.e. MME) may provide LIPA for this UE. Furthermore, in the absence of any LIPA information for the requested APN from the HSS, the VPLMN (i.e MME) shall not provide LIPA. The VPLMN address allowed flag is not considered when establishing a LIPA PDN connection.
LIPA is supported for APNs that are valid only when the UE is connected to a specific CSG. LIPA is also supported for "conditional" APNs that can be authorized to LIPA service when the UE is using specific CSG. APNs marked as "LIPA prohibited" or without a LIPA permission indication cannot be used for LIPA.
MME shall release a LIPA PDN connection to an APN if it detects that the UE's LIPA CSG authorization data for this APN has changed and the LIPA PDN connection is no longer allowed in the current cell.
As mobility of the LIPA PDN connection is not supported in this release of the specification, the LIPA PDN connection shall be released when the UE moves away from H(e)NB. Before starting the handover procedure towards the target RAN, the H(e)NB shall request using an intra-node signalling the collocated L-GW to release the LIPA PDN connection. The H(e)NB determines that the UE has a LIPA PDN connection from the presence of the Correlation ID in the UE (E-)RAB context. The L-GW shall then initiate and complete the release of the LIPA PDN connection using the PDN GW initiated bearer deactivation procedure as per clause 5.4.4.1 or GGSN initiated PDP context deactivation procedure as specified in TS 23.060 [7]. The H(e)NB shall not proceed with the handover preparation procedure towards the target RAN until the UE's (E-)RAB context is clear for the Correlation ID.
At the handover, the source MME checks whether the LIPA PDN connection has been released. If it has not been released:
- and the handover is the S1-based handover or the Inter-RAT handover, the source MME shall reject the handover.
- and the handover is X2-based handover, the MME shall send a Path Switch Request Failure message (see more detail in TS 36.413 [36]) to the target HeNB. The MME performs explicit detach of the UE as described in the MME initiated detach procedure of clause 5.3.8.3.
NOTE 2: The direct signalling (implementation dependent) from the H(e)NB to the L-GW is only possible since mobility of the LIPA PDN connection is not supported in this release.
During idle state mobility events, the MME/SGSN shall deactivate the LIPA PDN connection when it detects that the UE has moved away from the HeNB.
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4.3.17 Support for Machine Type Communications (MTC)
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4.3.17.1 General
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This clause provides an overview about functionality for Machine Type Communications according to service requirements described in TS 22.368 [66]. The specific functionality is described in the affected procedures and features of this and other specifications. For discrepancies between this overview clause and the detailed procedure and function descriptions, the latter take precedence.
MTC functionality is provided by the visited and home networks when the networks are configured to support machine type communication. It applies to both the non-roaming case and the roaming case and some functionality may be dependent upon the existence of appropriate roaming agreements between the operators.
Some of the MTC functions are controlled by subscriber data. Other MTC functions are based on indicators sent by the UE to the network. MTC functionality is performed by UEs that are configured to support different options as described in clause 4.3.17.4.
Though motivated by scenarios and use cases defined in TS 22.368 [66], the functions added to support MTC have general applicability and are in no way constrained to any specific scenario or use case except where explicitly stated.
Unless otherwise stated in this specification, MTC functionality also applies over satellite access.
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4.3.17.2 Overview of protection from Potential MTC Related Overload
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The number of MTC devices may be several orders of magnitude greater than "traditional" devices. Many (but not all) MTC devices will be relatively stationary and/or generate low volumes of traffic. However, these UEs have the capability to generate normal quantities of signalling. As normal signalling from large numbers of UEs may cause overload independently whether the UE is used for MTC or not, generic functionality for overload and congestion control is required.
The total signalling from large numbers of UEs is a concern in at least two situations:
- when an application (running in many UEs) requests many UEs to do "something" at the same time; and/or
- when many UEs are roamers and their serving network fails, then they can all move onto the local competing networks, and potentially overload the not (yet) failed network(s).
To counter these potential problems, the following standardised indications and mechanisms are provided in a generic manner. These permit node specific features to be developed to protect the networks.
a) Where applicable, UEs can be configured for enhancements as described in subsequent bullets Post-manufacturing configuration can be performed remotely as described in clause 4.3.17.4.
b) For mobile originated services, UEs configured for low access priority provide the E-UTRAN with information indicating that the RRC connection establishment request has low access priority (see clause 4.3.17.4). Clause 4.3.17.4 describes when low access priority is not applicable.
c) RRC signalling has the capability of providing 'extended wait timers' when rejecting messages from UEs. These 'extended wait timers' are only used by UEs that access the network with low access priority.
d) The MME can initiate rejection of RRC connection establishments in the E-UTRAN for UEs that access the network with low access priority as described in clause 4.3.7.4.1. In addition, MME signalling or O&M can trigger E-UTRAN to initiate Extended Access Barring. These mechanisms are further described in clause 4.3.7.4.1.
e) Overload messages from the MME to E-UTRAN are extended to aid the RAN in performing the functionality in bullets b, c and d above.
f) UEs configured with a long minimum periodic PLMN search time limit (see TS 24.368 [69]) have an increased minimum time in between their searches for more preferred PLMNs.
NOTE 1: Following the failure of a more preferred PLMN, UEs configured as above might change to other local competing networks. Expiry of this search timer will lead to the UE re-attempting to access the failed network, and then, if that network has not yet recovered, reaccessing one of the local competing networks. Use of a too short timer for the more preferred PLMN search can both prevent the failed network from recovering, and, impose more load on the local competing networks.
g) At PLMN change, UEs configured to perform Attach with IMSI at PLMN change (see TS 24.368 [69]) do this rather than a TA update with GUTI (thus avoiding the need to reject the TA update, and to request the IMSI following the subsequent Attach with GUTI).
NOTE 2: In the case of a network failure, this reduces the message processing load on a local competing network and hence makes that network more likely to survive the failure of the other network.
h) For mobile originated services, UEs configured for low access priority (see TS 24.368 [69]) provide a low access priority indication to the MME in NAS signalling that permit the MME to undertake protective measures (e.g. to permit the MME to immediately command the UE to move to a state where it does not need to generate further signalling messages and/or does not reselect PLMNs), as described in clause 4.3.7.4.1. Clause 4.3.17.4 describes when low access priority is not applicable.
i) Using Periodic TAU timer value sent by the HSS and/or UE provided low access priority indication (bullet h above), the MME can allocate a long periodic TAU timer value to the UE. A long periodic TAU timer is likely to slow down the rate at which a UE detects a network failure and thus it slows down the rate of movement of UEs from a failed network to other local competing networks (see clause 4.3.17.3).
j) Mechanisms for the MME and P-GW to detect congestion associated with a particular APN (see clauses 4.3.7.4.2 and 4.3.7.5).
k) The addition of 'back off timers' to EMM and ESM signalling messages (e.g. to rejection messages). These include some time randomisation to guard against a repeat of a load peak. The MME should be able to apply this behaviour on a per-APN basis. as described in clause 4.3.7.4.2
l) Signalling that permits the P-GW to request the MME to generate the above ESM signalling with 'back off timers' (see clause 4.3.7.5).
m) An MME overload control mechanism to selectively limit the number of Downlink Data Notification requests the S-GW sends to the MME for downlink low priority traffic received for UEs in idle mode (see clause 4.3.7.4.1a).
n) UE configured for specific handling of the invalid USIM state, the "forbidden PLMN list", the "forbidden PLMNs for attach in S1mode list" and the "forbidden PLMNs for GPRS service list" remembers that the USIM is invalid and keeps the PLMN forbidden lists even if the UE is switched off and then switched on.
o) When the UE has an activated PDN connection without low access priority or the UE is requested to establish such a PDN connection and the UE is configured with a permission for overriding low access priority the UE doesn't provide a low access priority indication to the MME in NAS MM signalling and also not to the RAN in the RRC requests. In the NAS request for activating a PDN connection this UE always indicates what the upper layers requested, i.e. the UE indicates low access priority in that NAS request unless the upper layers request activation of a PDN connection without low access priority.
p) When the UE has an activated PDN connection that is without low access priority or the UE is requested to activate such a PDN connection and the UE is configured with a permission for overriding Extended Access Barring, then the UE ignores any Extended Access Barring (if it is activated in the network) as defined in TS 22.011 [67].
NOTE 3: It is assumed that the mechanisms described in this entire clause are designed by Stage 3 in a manner that allows extensibility and forward compatibility.
q) The eNodeB may use the low access priority indication provided by the UE to steer UEs configured for low access priority to specific MMEs.
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4.3.17.3 Optimising periodic TAU Signalling
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To reduce network load from periodic TAU signalling and to increase the time until the UE detects a potential need for changing the RAT or PLMN (e.g. due to network problems) the longer values of the periodic TAU timer and Mobile Reachable timer shall be supported.
A long periodic RAU/TAU timer value may be locally configured at MME or may be stored as part of the subscription data in HSS. During Attach and TAU procedures the MME allocates the periodic RAU/TAU timer value as periodic TAU timer to the UE based on VPLMN operator policy, low access priority indication from the UE, periodic RAU/TAU timer value requested by UE, subscription information received from the HSS and Start of Unavailability Period and/or Unavailability Period Duration if using a RAN that provides discontinuous coverage (see clause 4.13.8.2).
If MME receives a subscribed periodic RAU/TAU timer value from the HSS it allocates the subscribed value to the UE as periodic TAU timer. A visited PLMN MME may use subscribed periodic RAU/TAU timer value, if available, as an indication to decide for allocating a locally configured periodic RAU/TAU timer value to the UE.
If no subscribed periodic RAU/TAU timer value is received from the HSS, the MME should:
- if the periodic RAU/TAU timer value requested by UE is within the boundaries of the VPLMN operator policy, allocate the value requested by the UE;
- if the periodic RAU/TAU timer value requested by UE is higher than allowed per the VPLMN operator policy, allocate the highest allowed value per the VPLMN operator policy;
- if the periodic RAU/TAU timer value requested by UE is lower than allowed per the VPLMN operator policy, allocate the lowest allowed value per the VPLMN operator policy.
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4.3.17.4 UE configuration and usage of indicators
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A subscriber can by agreement with its operator be required to use UEs that are configured (see TS 24.368 [69]) to support one or more of the following options:
- UE configured for low access priority; and/or
- UE configured with a permission for overriding low access priority, which is only applicable for a UE that is also configured for low access priority; and/or
- UE configured to perform Attach with IMSI at PLMN change; and/or
- UE configured with a long minimum periodic PLMN search time limit; and/or
- UE configured for specific handling of the invalid USIM state, the "forbidden PLMN list", the "forbidden PLMNs for attach in S1mode list" and the "forbidden PLMNs for GPRS service list"; and/or
- UE configured for Extended Access Barring; and/or
- UE configured with a permission for overriding Extended Access Barring, which is only applicable for a UE that is also configured for Extended Access Barring.
NOTE 1: When a UE is accessing the network with low access priority, then the UE may be subject for longer backoff timers at overload and consequently need to be designed to be tolerant to delays when accessing the network.
UEs can be configured for one or more of the above options with the following restrictions:
- in this Release of the specification, a UE that is configured for low access priority shall also be configured for Extended Access Barring; and
- in this Release of the specification, a UE that is configured for Extended Access Barring shall be configured for low access priority.
- in this Release of the specification, a UE that is configured for overriding low access priority shall also be configured for overriding Extended Access Barring; and
- in this Release of the specification, a UE that is configured for overriding Extended Access Barring shall also be configured for overriding low access priority.
UEs can be configured for one or more of the above options. Post-manufacturing configuration of these options in the UE can be performed only by OMA DM or (U)SIM OTA procedures. UEs capable of the above options should support configuration of these options by both OMA DM and (U)SIM OTA procedures.
A UE configured for low access priority shall transmit the low access priority indicator to the MME during the appropriate NAS signalling procedures and transmit the corresponding low access priority to the E-UTRAN during RRC connection establishment procedures.
NOTE 2: The low access priority indicator in NAS signalling and the corresponding low access priority for RRC connection establishment are used by the network to decide whether to accept the NAS request or the setup of the RRC connection respectively.
Low access priority shall not be applicable in the following situations:
- for all procedures related to an emergency PDN connection; used for IMS Emergency sessions that are to be prioritized as per the requirements for IMS Emergency session procedures (see clause 4.3.12). When an emergency PDN connection gets established, the MME may, based on MME configuration, initiate the deactivation of any non-emergency PDN connection using the MME requested PDN disconnection procedure described in clause 5.10.3;
- for all procedures when preferential access to the network is provided to the UE by the Access Class 11-15 mechanism according to TS 36.331 [37] and TS 22.011 [67] e.g. for Multimedia Priority Services as described in clause 4.3.18;
NOTE 3: The configuration of a UE for low access priority and Access Class 11-15 are configured independently of each other. However, the home operator can take care to prevent a subscription for Access Class 11-15 from being used in a UE configured for low access priority.
- for RRC connection establishment procedures when responding to paging;
- for a UE configured with a permission for overriding low access priority under conditions described by bullet o in clause 4.3.17.2; or
- other specific situations described in TS 24.301 [46].
If the NAS session management request message used to establish a new PDN connection contains a low access priority indication, the MME shall forward the low access priority indication in the Create Session Request message to the S-GW/P‑GW. The low priority indication gets associated with a PDN connection when it is established and it shall not change until the PDN connection is deactivated.
The low access priority indication may be included in charging records by the visited and home networks. In order to permit the S-GW to include the low access priority indicator in the charging records, the low access priority indicator should be stored in the MME EPS Bearer contexts and should be passed as part of these contexts to other SGSN/MME or S-GW nodes in mobility management procedures.
NOTE 4: In this release there is no other usage of storing the low access priority indicator in EPS Bearer contexts other than for the purpose to include it in charging records. Particularly, the low access priority indicator in EPS Bearer contexts is not used by the network to make overload control decisions.
A network node may invoke one or more of the following mechanisms based on the indicators received in signalling from UEs or forwarded by other network nodes:
- based on the low access priority indicator in NAS request messages, bullets e, h, i, k and l as defined in clause 4.3.17.2; and/or
- based on the low access priority for RRC connection establishment, bullets b, c and q as defined in clause 4.3.17.2.
A UE shall invoke one or more of the following mechanisms based on the configuration and capabilities of the UE:
- when UE is configured with a long minimum periodic PLMN search time limit, the UE invokes actions as described in bullet f in clause 4.3.17.2; and/or
- when UE is configured to perform Attach with IMSI at PLMN change, the UE invokes actions as described in bullet g in clause 4.3.17.2; and/or
- when a UE is configured for low access priority, the UE invokes actions as described in bullets b and h in clause 4.3.17.2; and/or
- when UE is configured for specific handling of the invalid USIM state, the "forbidden PLMN list", the "forbidden PLMNs for attach in S1mode list" and the "forbidden PLMNs for GPRS service list", the UE invokes actions as defined in bullet n in clause 4.3.17.2; and/or
- when UE is configured for Extended Access Barring, the UE invokes actions as defined in bullet d in clause 4.3.17.2; and/or
- when a UE is configured with a permission for overriding low access priority and configured with a permission for overriding Extended Access Barring, the UE invokes actions as described in bullets o) and p) in clause 4.3.17.2.
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4.3.17.5 Void
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4.3.17.6 Support of UEs configured for low access priority, Extended Access Barring and permission for override
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The feature is specified in TS 23.060 [7] clause 5.3.13.6.
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4.3.17.7 High latency communication
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Functions for High latency communication may (depending on operator configuration) be used to handle mobile terminated (MT) communication with UEs being unreachable while using power saving functions (e.g. UE Power Saving Mode (see clause 4.3.22) or extended idle mode DRX (see clause 5.13a)) or UEs that are using a satellite access with discontinuous coverage. "High latency" refers to the initial response time before normal exchange of packets is established. That is, the time it takes before a UE has woken up from its power saving state and responded to the initial downlink packet(s). The feature is described in TS 23.682 [74].
The High latency communication includes invoking extended buffering of MT data at the Serving GW when the UE is in a power saving state and not reachable. The handling is specified in the Network Triggered Service Request procedure, clause 5.3.4.3. Establishing the user plane for delivering the buffered data when the UE contacts the MME or SGSN by signalling shall be done in the Tracking Area Update and Routing Area Update procedures. The MME/SGSN uses its parameter DL Data Buffer Expiration Time in the MM context information to remember if there is buffered DL data to be delivered when the UE becomes reachable. When set, the DL Data Buffer Expiration Time shall be cleared at any user plane setup to the RAN, i.e. buffered DL data can been delivered. At TAU/RAU procedures with MME/SGSN change, the old MME/SGSN shall indicate in the context response to the new MME/SGSN that buffered DL data is waiting and hence the new MME/SGSN shall establish the user plane for delivery of the buffered DL data. When the DL Data Buffer Expiration Time has expired, the MME/SGSN considers no DL data to be buffered and no indications of Buffered DL Data Waiting are sent during context transfers at TAU procedures. At TAU/RAU procedures with Serving GW change, the buffered DL data is forwarded to the new Serving GW or Gn/Gp-SGSN.
For Control Plane CIoT EPS Optimisation, the High latency communication includes invoking the buffering of MT data at the Serving GW or the MME as specified in Mobile Terminated Data Transport in Control Plane CIoT EPS Optimisation with P-GW connectivity, clause 5.3.4B.3. When the UE contacts MME, MME delivers the buffered data using NAS PDUs. If MT data is buffered in MME, at TAU procedures with MME change the buffered data in the old MME is discarded.
The High latency communication also includes sending event notifications to application servers that have requested "UE Reachability" or "Availability after DDN failure" monitoring events. Event notifications are sent when a UE becomes reachable, for example as part of the Attach Procedure, TAU/RAU procedures and the UE triggered Service Request procedure.
When "UE Reachability" monitoring is requested for UE's that are using extended idle mode DRX, an event notification is sent to the application server when the UE is about to become reachable for paging.
If the MME is aware that some signalling or data is pending in the network for an UE that is known as being unreachable for a long duration, e.g. for UE's having extended idle mode DRX or PSM enabled, the MME may include a Pending Data indication in the next S1-AP message towards an eNodeB. If the eNodeB receives this indication, the eNodeB may take this information into account when determining user inactivity. At inter-RAN node handovers, if some signalling or data are still pending, the target MME may send a Pending Data indication to the target RAN node.
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4.3.17.8 Support for Non-IP Data Delivery (NIDD)
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4.3.17.8.1 General
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The support of Non-IP data is part of the CIoT EPS Optimisations. A PDN Type "Non-IP" is used for Non-IP data. The Non-IP data delivery to SCS/AS is accomplished by one of two mechanisms:
- Delivery using SCEF as defined in clause 4.3.17.8.3.2.
- Delivery using a Point-to-Point (PtP) SGi tunnel as defined in clause 4.3.17.8.3.3.
When the Reliable Data Service is not used, Non-IP data in-sequence delivery cannot be guaranteed and data PDUs may be lost requiring higher protocol layers to ensure guaranteed delivery when needed. The Reliable Data Service is defined in TS 23.682 [74].
NOTE: If UEs use protocols that require broadcast/multicast mechanisms (e.g. use "IP stacks" on top of PDN connections of type "Non-IP"), this may cause increased traffic and power consumption to the UE and the network.
The SMS service may also be used to deliver data without use of the IP protocol. The SMS service is always supported for CIoT EPS Optimisations, i.e. can be used simultaneously with Non-IP and IP data. When only the SMS service is needed, an attach without PDN connection establishment can be used, see clause 5.3.2.
Dedicated bearers are not supported for the Non-IP data.
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4.3.17.8.2 ESM Procedures
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The UE indicates in the ESM connection request, e.g. in Attach or PDN Connectivity Request, that a Non-IP PDN type shall be used. The subscription information has a default APN for PDN Type Non-IP, which the MME uses for the first received Non-IP connectivity request unless the UE has included an APN in the request.
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4.3.17.8.3 Delivery mechanism
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4.3.17.8.3.1 General
At each PDN connectivity request, the MME decides which delivery mechanism (SCEF based delivery or SGi based delivery) is used for delivering the Non-IP data between RAN and AS. An indication associated with the used APN determines if SCEF based delivery or SGi based delivery shall be used.
4.3.17.8.3.2 SCEF based delivery
When the MME decides to use SCEF based delivery mechanism for Non-IP data, a PDN connection is established towards the selected SCEF. Such a PDN Connection is also known as an "SCEF Connection". The APN used for SCEF based delivery is an FQDN, which either resolves to an SCEF hostname or to an SCEF IP address.
The SCEF based delivery is applicable only to the Control Plane CIoT EPS Optimisation (see clause 4.10).
The support of Non-IP data via the SCEF is further defined in TS 23.682 [74].
4.3.17.8.3.3 SGi based delivery
4.3.17.8.3.3.1 General
When support of Non-IP data is provided at the SGi interface, different point-to-point tunnelling techniques may be used. Point-to-point tunnelling by UDP/IP encapsulation can be used as described in clause 4.3.17.8.3.3.2 below. Other techniques as described in clause 4.3.17.8.3.3 below may be used.
Support for the SGi based delivery of Non-IP data can be used by any UE. That is, it is independent of support for the User Plane CIoT EPS Optimisation and the Control Plane CIoT EPS Optimisation (see clause 4.10).
The P-GW decides at PDN connection establishment based on pre-configuration which point-to-point tunnelling technique is used for the SGi based delivery between the P-GW and the AS.
NOTE: The pre-configuration can be done in the P-GW per APN or based on other criterion such as SLA between operator and 3rd party application service provider, etc.
4.3.17.8.3.3.2 SGi PtP tunnelling based on UDP/IP
SGi PtP tunnelling based on UDP/IP may be used to deliver Non-IP data to AS via SGi.
A point-to-point tunnel is used by the P-GW towards the AS. The tunnel parameters (i.e. destination IP address and UDP port) for SGi PtP tunnelling based on UDP/IP are pre-configured on the P-GW. IP address allocation procedures for PDN connections are performed locally (e.g. without involving the UE) by the P-GW based on APN configuration and according to clause 5.3.1. Only single IP address is used (i.e. both IPv4 and IPv6 addresses are not allocated).
The P-GW acts as a transparent forwarding node for the payload between the UE and the AS.
For uplink Non-IP data, the P-GW forwards the received data to the AS over the SGi PtP tunnel using UDP/IP encapsulation. When the Reliable Data Service is enabled, the P-GW processes the Reliable Data Service Header. The Reliable Data Service Configuration is pre-configured on the P-GW. The Reliable Data Service Configuration is defined in TS 23.682 [74].
For downlink Non-IP data, the AS sends the data using UDP/IP encapsulation with the IP address of the UE and the 3GPP defined UDP port for "Non-IP" data. The P-GW decapsulates the received data (i.e. removes the UDP/IP headers) and forwards the data to S-GW on the GTP-U tunnel identified by the IP address of the UE (i.e. PDN connection) for delivery to the UE. When the Reliable Data Service is enabled, the P-GW adds the Reliable Data Service Header.
The P-GW performs the IP related operations (e.g. allocates IP address for the PDN connection), but the IP address or IP prefix is not provided to the UE (i.e. SLAAC / Router Advertisements are not performed. DHCP or DHCPv6 are not used). In the case of IPv6 the P-GW assigns an Interface Identifier for the PDN connection. The allocated IP address or IPv6 prefix identifies the PDN connection of the UE. The P-GW shall inform the MME of the assigned IPv4 address or IPv6 prefix and Interface Identifier for a PDN Connection of a given UE. However, the UE is not informed about the assigned IPv6 prefix and Interface Identifier.
NOTE: It is recommended to use IPv6 for CIoT. IPv4 based addressing is deprecated for machine type communication used over 3GPP accesses, see TS 23.221 [27].
4.3.17.8.3.3.3 Other SGi PtP tunnelling mechanisms
SGi PtP tunnelling mechanisms such as PMIPv6/GRE, L2TP, GTP-C/U, etc, may be used to deliver Non-IP data to AS via SGi. The general handling of such delivery mechanisms is as described below.
A point-to-point tunnel is established by the P-GW towards the AS. Depending on the type of protocol employed on the SGi PtP tunnel, the SGi PtP tunnel setup may be done at the time of Attach or at the time of first MO datagram being sent by the CIoT UE. The P-GW selects the AS based on the P-GW configuration (e.g. per APN, or per PtP tunnel type etc.). However, IP address allocation procedures for the UE (according to clause 5.3.1) are not performed by the P-GW.
NOTE: An AS can be dedicated for handling a specific Non-IP data protocol.
The P-GW acts as a transparent forwarding node between the UE and the AS.
For uplink Non-IP data, the P-GW forwards the received data to the AS over the established SGi PtP tunnel.
For downlink Non-IP data, the AS locates the right SGi PtP tunnel for the UE (using information such as UE identifiers in the Non-IP protocol itself, etc) to forward the data. The AS sends the data to P-GW over the established SGi PtP tunnel. The P-GW in turn sends the data to S-GW on the GTP-U tunnel identified by the associated SGi PtP tunnel for delivery to the UE.
4.3.17.8a Support of PDN type Ethernet
The support of Ethernet PDN type relies upon the selection of a P-GW that supports combined PGW+SMF functionality specified in TS 23.501 [83], TS 23.502 [84] and TS 23.503 [88]. This functionality may be supported by a PLMN even if it has no NG-RAN coverage, however, it does require that the subscriber has a subscription record in the 5GS UDM.
This feature is described in clause 5.6.10.2 of TS 23.501 [83].
For PDN connection with Ethernet PDN type, IP address allocation is not needed.
In contrast to the Non-IP PDN type, EPS Dedicated Bearers are supported for the Ethernet PDN type (including the TFT as described in clause 4.7.2.1). The details about the TFT packet filter(s) are described in clause 5.7.6.3 of TS 23.501 [83].
For PDN connection of Ethernet type, dynamic PCC is applied as described in clause 4.7.5 with the following differences:
- Dynamic PCC specified in TS 23.503 [88] is applied, i.e. the PCEF interacts with the PCF using N7 interface as described in TS 23.501 [83], and the PCEF does not interact with the PCRF using Gx interface as specified in TS 23.203 [6].
- The SDF template included in the PCC rule(s) uses Ethernet packet filter as specified in TS 23.501 [83].
- The description related to IP address configuration is not applicable.
Dedicated Core Network functionality (see clause 4.3.25) can be used to avoid the need for all MMEs in the PLMN to be upgraded to support Ethernet PDN Type.
If the UE's attempt to use the Ethernet PDN Type is rejected by the network, the UE may attempt to gain service by requesting the Non-IP PDN type.
Ethernet PDN Type is not supported in GERAN/UTRAN. If the UE only has an Ethernet PDN connection established, mobility to GERAN/UTRAN should be prevented. To do this, the MME shall indicate to the eNodeB in Handover Restriction List that GERAN/UTRAN is restricted.
For PDN connection with Ethernet PDN type, mobility to Non 3GPP access to EPC is not supported.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.17.9 Service Gap Control
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Service Gap Control is an optional feature intended for MTC/CIoT UEs to control the frequency at which these UEs can access the network. That is, to ensure a minimum time gap between consecutive Mobile Originated data communications initiated by the UE. This helps reducing peak load situations when there are a large number of these UEs in an operator network. Service Gap Control is intended to be used for "small data allowance plans" for MTC/CIoT UEs where the applications are tolerant to service latency.
NOTE 1: Time critical applications, such as emergency services and regulatory prioritised services can suffer from the latency caused by the Service Gap Control feature. Therefore Service Gap Control feature is not recommended for subscriptions with such applications and services.
Service Gap Time is a subscription parameter used to set the Service Gap timer and is enforced in the UE and in the MME on a per UE level (i.e. the same Service Gap Timer applies for all PDN connections that the UE has). The UE indicates its capability of support for Service Gap Control in the Attach Request message and TAU Request message to the MME. The MME passes the Service Gap Time to the UE in the Attach Accept message and/or Tracking Area Update Accept message for UE that has indicated its supports of the Service Gap Control. The Service Gap Control shall be applied in a UE when a Service Gap Time is stored in the UE context and applied in the MME when the Service Gap Time is stored in the MM context.
Service Gap Control requires the UE to stay in ECM-IDLE mode for at least the whole duration of the Service Gap timer before triggering Mobile Originated user data transmission, except for procedures that are exempted (see TS 24.301 [46]). The Service Gap timer shall be started each time a UE moves from ECM-CONNECTED to ECM-IDLE, unless the connection request was initiated by the paging of a Mobile Terminated event, or after a TAU procedure without active flag or signalling active flag, which shall not trigger a new or extended Service Gap interval. When a Service Gap timer expires, the UE is allowed to send a connection request again. If the UE does so, the Service Gap timer will be restarted at the next ECM-CONNECTED to ECM-IDLE transition.
The Service Gap control is applied in ECM-IDLE state only and does not impact UE Mobile Originated user data transmission or Mobile Originated signalling in ECM-CONNECTED state. The Service Gap timer is not stopped upon ECM-IDLE state to ECM-CONNECTED state transition. The UE shall not initiate connection requests for MO user plane data, MO control plane data, or MO SMS when a Service Gap timer is running. The UE shall also not initiate Attach Requests when a Service Gap timer is running, unless it is Attach Request without PDN connectivity or Emergency Attach which are allowed.
NOTE 2: As a consequence of allowing Attach without PDN connectivity procedure, the UE with a running Service Gap timer does not initiate further MO signalling, except for tracking area updating procedure, until the UE receives MT signalling or after the UE has moved to ECM-IDLE state and the Service Gap Timer is not running.
NOTE 3: Implementations need to make sure that latest and up-to-date data are always sent when a Service Gap timer expires.
The MME may enforce the Service Gap timer by rejecting connection request for MO user plane data, MO control plane data, or MO SMS when a Service Gap timer is running. The MME may enforce the Service Gap timer by not allowing Attach Requests when a Service Gap timer is running, unless it is Attach Request without PDN connectivity or Emergency Attach which are allowed. When rejecting the connection requests and the Attach Requests while the Service Gap timer is running, the MME may include a Mobility Management back-off timer corresponding to the time left of the current Service Gap timer. For the UEs that does not support Service Gap Control (e.g. pre-release-15 UEs), Service Gap Control may be enforced using "General NAS level Mobility Management control" as defined in clause 4.3.7.4.2.1.
When the MME starts the Service Gap timer, the MME should invoke the Service Gap timer with a value that is slightly shorter than the Service Gap Time value provided to the UE in the subscription information received from the HSS.
NOTE 4: This ensures that the MME doesn't reject any UE requests just before the Service Gap timer expires e.g. because of slightly unsynchronized timers between UE and MME.
A UE which transitions from a PSM or eDRX power saving state shall apply Service Gap Control when it wakes up if the Service Gap timer is still running.
Additional aspects of Service Gap Control:
- Service Gap Control applies in all PLMNs.
- When the Service Gap timer is running and the UE receives paging, the UE shall respond as normal.
- Service Gap Control applies to low priority (delayTolerant) and normal traffic.
- Service Gap Control does not apply to exception reporting for NB-IoT.
- Emergency Attach and Attach without PDN Connectivity are allowed when a Service Gap timer is running.
- Service Gap Control shall be effective also for UEs performing detach and reattach unless it is Attach Request without PDN connectivity or Emergency Attach.
- Tracking Area Update with active flag or signalling active flag is not allowed when a Service Gap timer is running except for emergency bearer services or if the UE is accessing with high priority access class in the range AC 11-15.
- If the Service Gap timer is running, the Service Gap is applied at PLMN selection as follows:
a) Re-attach to the registered PLMN: The remaining Service Gap timer value survives and controls the re-attach.
b) Attach or Tracking Area Update to a different PLMN: The remaining Service Gap timer value survives and controls the Attach/Tracking Area Update to the new PLMN.
c) USIM swap: The Service Gap timer is no longer running and the Service Gap feature does not apply, unless re-instatiated by the serving PLMN.
- Multiple uplink packets and downlink packets are allowed during one RRC connection for UE operating within its APN Rate Control limits.
The following procedures are impacted by Service Gap Control:
- E-UTRAN Initial Attach, see clause 5.3.2.1;
- Tracking Area Update procedures, see clause 5.3.3;
- UE Triggered Service Request, see clause 5.3.4.1;
- Connection Resume Request, see clause 5.3.5A.
NOTE 5: Since UE triggered Service Request and Connection Resume Request are prevented by Service Gap timer, this implicitly prevents the UE from initiating MO data in Control Plane EPS Optimisations (see clause 5.3.4B.2), MO NIDD procedure (see TS 23.682 [74]) and MO SMS (see TS 23.272 [58]).
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.18 Multimedia Priority Service
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.18.1 General
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Multimedia Priority Service (MPS) allows certain subscribers (i.e. Service Users as per TS 22.153 [68]) priority access to system resources in situations such as during congestion, creating the ability to deliver or complete sessions of a high priority nature. Service Users are government-authorized personnel, emergency management officials and/or other authorized users. MPS supports priority sessions on an "end-to-end" priority basis.
MPS is based on the ability to invoke, modify, maintain and release sessions with priority, and deliver the priority media packets under network congestion conditions. MPS is supported in a roaming environment when roaming agreements are in place and where regulatory requirements apply.
NOTE 1: If a session terminates on a server in the Internet (e.g. web-based service), then the remote end and the Internet transport are out of scope for this specification.
MPS is supported for Service Users using UEs connecting via 3GPP access. MPS is also supported for Service Users using UEs that support connecting via Trusted or Untrusted non-3GPP access via WLAN as specified in TS 23.402 [2] for MPS. ePDG selection is according to clause 4.5.4 in TS 23.402 [2].
A Service User obtains priority access to the Radio Access Network by using the Access Class Barring mechanism according to TS 36.331 [37] and TS 22.011 [67]. This mechanism provides preferential access to UEs based on its assigned Access Class. If a Service User belongs to one of the special access-classes as defined in TS 22.011 [67], the UE has preferential access to the network compared to ordinary users in periods of congestion.
MPS subscription allows users to receive priority services, if the network supports MPS. The same MPS subscription applies to access via 3GPP access and non-3GPP access via WLAN. MPS subscription entitles a USIM with special Access Class(es). MPS subscription includes indication for support of Priority EPS Bearer Service, IMS priority service and CS Fallback priority service support for the end user. Priority level regarding Priority EPS Bearer Service and IMS are also part of the MPS subscription information. The usage of priority level is defined in TS 23.203 [6] and TS 23.228 [52].
An MPS subscription may include an optional MPS for Messaging indication which sets(enables)/clears(disables) the MPS priority treatment of messaging service (i.e. SMS over NAS, SMS over IP and messaging over IMS are all controlled by one indication). The MPS for Messaging indication is used in EPC entities and is not delivered to the UE. The detailed MPS for Messaging indication handling is further specified in TS 23.272 [58] for SMS over NAS via MME, in TS 23.204 [95] for SMS over IP and in TS 23.228 [52] for messaging over IMS. The MPS for Messaging indication in subscription data may be provisioned via SCS/AS as specified in TS 23.682 [74].
NOTE 2: The MPS subscription on the USIM is also used for 3GPP procedures with priority treatment over WLAN for UEs that support MPS over Trusted and Untrusted non-3GPP access via WLAN feature.
NOTE 3: The above statements for the Priority EPS Bearer Service are also applicable for the MPS for Data Transport Service.
An MPS Service User is treated as an On Demand MPS subscriber or not, based on regional/national regulatory requirements. On Demand service is based on Service User invocation/revocation explicitly and applied to the PDN connections for an APN. When not On Demand, MPS service does not require invocation, and provides priority treatment for all EPS bearers for a given Service User after attachment to the EPS network.
NOTE 4: According to regional/national regulatory requirements and operator policy, On-Demand MPS Service Users can be assigned the highest priority.
Since the Service User has an access class within the range for priority services, the Establishment Cause in RRC connection request is set to highPriorityAccess. When the eNodeB receives mobile initiated signalling with establishment cause set to highPriorityAccess, the eNodeB handles the RRC connection request with priority. When the MME receives and verifies mobile initiated signalling with establishment cause set to highPriorityAccess, the MME establishes the S1 bearer with priority.
The terminating network identifies the priority of the MPS session and applies priority treatment, including paging with priority, to ensure that the MPS session can be established with priority to the terminating user (either a Service User or normal user).
Priority treatment for MPS includes priority message handling, including priority treatment during authentication, security, and location management procedures.
Priority treatment for MPS session requires appropriate ARP and QCI (where necessary for non-GBR bearers) setting for bearers according to the operator's policy.
When an MPS session is requested by a Service User, the following bearer management principles apply in the network:
- EPS bearers (including default bearer) employed in an MPS session shall be assigned ARP value settings appropriate for the priority level of the Service User.
- Setting ARP pre-emption capability and vulnerability for MPS bearers, subject to operator policies and depending on national/regional regulatory requirements.
- Pre-emption of non-Service Users over Service Users during network congestion situation, subject to operator policy and national/regional regulations.
Priority treatment is applicable to IMS based multimedia services, priority EPS bearer services (PS data without IMS interaction) and CS Fallback.
For Multimedia Priority services any EPC functions, procedures and capabilities are provided according to this clause's specification except when specified differently in the following clauses.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.18.2 IMS-based Multimedia Priority Services
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23.401
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4.3.18.2.1 Originating IMS-based MPS Session
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IMS based MPS sessions are permitted to be originated from any UE, in addition to MPS-subscribed UEs.
The MPS-subscribed UE, based on the MPS IMS subscription information, operator's policy and national/regional regulations, may be given priority treatment for the default bearer and the EPS bearer carrying IMS signalling in the EPS prior to and during IMS-based MPS invocation. Further, priority treatment in the EPS for signalling and media bearers may be modified/established via dynamic PCC based on the session authorization information received from the AF.
As the IMS media bearer is established after the IMS session of the MPS service has been established, it can be assigned with correct ARP value when it is established. However IMS signalling related EPS bearer needs to be upgraded if it has not been assigned with an appropriate ARP setting for the MPS service when the IMS session of the MPS service has been initiated.
Also to avoid cases where the default bearer may not be allocated resources in the handover case, due to low ARP priority for the PDN connection, it is necessary to assure that the default bearer has an ARP setting appropriate for the MPS service.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.18.2.2 Terminating IMS-based MPS Session
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The terminating network identifies the priority of the IMS-based MPS session and applies priority treatment to ensure that the call is delivered with priority to the terminating user (either a Service User or normal user).
If the existing ARP of the default or dedicated EPS bearer that is used to transport IMS signalling are not appropriate for the MPS service, then PCRF updates to the appropriate settings.
S-GW triggers a new priority paging towards MME if the ongoing paging is lower priority than the incoming data received in the S-GW for IMS terminating session.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.18.3 Priority EPS Bearer Services
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The Service User receives on demand priority treatment according to its MPS profile, i.e. On-Demand. If the Service User is not authorized to use on-demand priority request, the Service User receives priority treatment (i.e. appropriate ARP and QCI ) at initial attach for all bearers, based on user profile data stored in the HSS/SPR and authorized by the PCRF (see TS 23.203 [6], clause 7.2).
An On-Demand Service User requires explicit invocation/revocation via SPR MPS user profile update (see TS 23.203 [6], clause 7.5). Since MPS user profile are part of inputs for PCC rules, the update will trigger PCC rules modification to achieve appropriate ARP and QCI settings for bearers (see TS 23.203 [6], clause 7.4.2).
When the eNodeB receives mobile initiated signalling with establishment cause set to highPriorityAccess, the eNodeB handles the RRC connection request with priority. When the MME receives and verifies mobile initiated signalling with establishment cause set to highPriorityAccess, the MME establishes the S1 bearer with priority. Based on MPS EPS priority subscription, MME can verify whether the UE is permitted to handle the request preferentially comparing to other UEs not prioritized.
An AF for MPS Priority Service is used to provide Priority EPS Bearer Services using network-initiated resource allocation procedures (via interaction with PCC) for originating accesses.
NOTE: Use of 3rd party AF for MPS services for Service Users is outside the scope of 3GPP specification.
4.3.18.3a MPS for Data Transport Service
MPS for Data Transport Service is an on-demand service that may be invoked/revoked by an authorized MPS Service User using a UE with a subscription for MPS (i.e. according to its MPS profile), or using a UE that does not have a subscription for MPS (using methods not in scope of this specification).
MPS for Data Transport Service requires explicit invocation. The Service User invokes the service by communicating with an AF. The authorization of an MPS for Data Transport Service request is done by the AF or by the PCRF according to clause 6.1.11.5 of TS 23.203 [6]. Upon successful authorization the PCRF performs the necessary actions to achieve appropriate ARP and QCI settings for the bearers (see clause 6.1.11.5 of TS 23.203 [6]).
NOTE 1: MPS for Data Transport Service can be applied to any APN other than the well-known APN for IMS.
MPS for Data Transport Service enables the prioritization of all traffic on the default bearer and other bearers upon AF request. The QoS modification to the default bearer and other bearers is done based on operator policy and regulatory rules by means of local PCRF configuration.
NOTE 2: If no configuration is provided, MPS for Data Transport Service applies only to the default bearer.
NOTE 3: MPS for Data Transport Service controls the priority of traffic on bearers independent of the application(s) being used. Other mechanisms (e.g., Priority EPS Bearer Service) can be used to control the priority of traffic on other bearers not under control by MPS for Data Transport Service, based on operator policy.
For MPS for Data Transport Service, the AF may also create an SDF for signalling priority between the UE and the AF (see clause 6.1.11.5 of TS 23.203 [6]).
NOTE 4: The network can hide its topology from the AF supporting MPS for Data Transport Service. At the same time, the UE needs to provide its locally known IP address to the AF supporting MPS for Data Transport Service to support Diameter routing to the applicable PCRF. Thus, there can be no NAT of the UE IP address between the PDN-GW and the AF supporting MPS for Data Transport Service.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.18.4 CS fallback
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CS Fallback allows users to fallback to GERAN/UTRAN/1x RTT while in E-UTRAN access thus allowing the network to transfer the call towards GERAN/UTRAN CS domain. In order to ensure that a priority CSFB call to/from a service user is given proper priority treatment in the EPS, MPS subscription indicates the user's CS priority status, i.e. MPS CS Priority, which is provided to MME with user's subscription information. When the eNodeB receives mobile initiated signalling with establishment cause set to highPriorityAccess, the eNodeB handles the RRC connection request with priority. When the MME receives and verifies mobile initiated signalling with establishment cause set to highPriorityAccess, the MME establishes the S1 bearer with priority.
Details on the priority treatment of CSFB, see TS 23.272 [58].
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.18.5 Network Congestion Controls for MPS
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Based on regional/national requirements and network operator policy, MPS shall be exempted from network congestion controls up to the point where further exemptions cause network instability. The MME should not apply NAS level congestion control for mobile initiated signalling with establishment cause set to highPriorityAccess. The MME should not apply congestion control for termination requests related with an ARP associated with MPS.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.18.6 Load Re-balancing between MMEs for MPS
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When a UE is in ECM-CONNECTED mode with a bearer having an ARP associated with MPS, the MME should not release the UE for load re-balancing, except under critical conditions such as the need to perform an MME node restart. The MME should wait until the UE initiates a TAU or becomes ECM-IDLE before initiating load re-balancing.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.19 Core Network node resolution
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.19.1 General
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The indication of mapped or native GUTI shall be signalled by the UE to the MME as an explicit indication in Attach Request and TAU Request messages. The indication of mapped or native P-TMSI/RAI shall be signalled by the UE to the SGSN as an explicit indication in Attach Request and RAU Request messages. The MME/SGSN resolves the old MME/SGSN using old GUTI respective old P-TMSI/RAI sent in the Attach request and TAU/RAU request messages, and determines if the old GUTI or the old P-TMSI/RAI is mapped or native by one of the following two methods:
- Indication using most significant bit (MSB) in LAC and MME Group ID.
- Explicit indication sent from UE to MME and SGSN.
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23.401
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4.3.19.2 MSB in LAC and MME Group ID
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For PLMNs deployed with such mechanism the MME differentiates between a GUMMEI mapped from P-TMSI/RAI and a native GUMMEI based on the value of most significant bit of the MME Group ID; i.e. the MSB is set to "0" then the GUMMEI is mapped from P-TMSI/RAI and if MSB is set to "1", the GUMMEI is a native one, as specified in TS 23.003 [9].
For PLMNs deployed with such mechanism the S4-SGSN differentiates between a P-TMSI/RAI mapped from GUTI and a native P-TMSI/RAI based on the value of most significant bit of the LAC; i.e. the MSB is set to "1" then the P‑TMSI/RAI is mapped from GUTI and if MSB is set to "0", the P-TMSI/RAI is a native one, as specified in TS 23.003 [9].
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.19.3 Explicit Indication
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For PLMNs deployed with such mechanism the MME differentiates between a GUTI mapped from P-TMSI/RAI or a native GUTI based on the explicit indication sent by the UE.
For PLMNs deployed with such mechanism the S4-SGSN differentiates between a P-TMSI/RAI mapped from GUTI or a native P-TMSI/RAI based on the explicit indication sent by the UE.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.20 Relaying function
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.20.1 General
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The relaying function enables an operator to improve and extend the coverage area by having a Relay Node (RN) wirelessly connected to an eNodeB serving the RN, called Donor eNodeB (DeNB), via a modified version of the E-UTRA radio interface called the Un interface as specified in TS 36.300 [5].
The relaying function and use of RN/DeNB entities in a network is transparent to the operations of the UEs connected to it and associated core network entities (e.g. MME, S/P-GW, PCRF etc.) for the UEs.
The relaying architecture is shown in figure 4.3.20.1-1.
Figure 4.3.20.1-1: Relaying Architecture
NOTE 1: Impact to core network elements from the introduction of RNs and DeNB is minimized by reusing the existing nodes and protocols when interacting with the core network.
NOTE 2: Functions of the MME for the RN and MME for the UE may be collocated in a single MME.
The RN supports the eNodeB functionality like termination of the radio protocols of the E-UTRA radio interface and the S1 and X2 interfaces. The RN also supports a subset of the UE functionality and protocols to wirelessly connect to the DeNB.
In addition to supporting eNodeB functionality, the DeNB also embeds and provides the S-GW/P-GW-like functions needed for the RN operation. This includes creating a session for the RN and managing EPS bearers for the RN as shown in clause 4.3.20.3, as well as terminating the S1-AP and S11 interfaces towards the MME serving the RN. Due to the proxy functionality, the DeNB appears as an MME (for S1), an eNodeB (for X2) and an S-GW to the RN.
The RN and DeNB also perform mapping of signalling and data packets onto EPS bearers that are setup for the RN. The mapping is based on existing QoS mechanisms defined for the UE and the P-GW and are described in TS 36.300 [5].
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.20.2 RN startup and attach procedure
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23.401
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4.3.20.2.1 General
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The startup procedure for the Relay Node is based on the normal UE attach procedure and consists of the following two phases:
- Phase I: Attach for RN preconfiguration.
- Phase II: Attach for RN operation (MME of the RN).
NOTE: When the certificate-based solution is used, the RN uses USIM-INI in Phase I and USIM-RN in Phase II with necessarily different IMSIs. When pre-shared key is used, there is only need for one USIM and the RN uses the same IMSI during Phase I and Phase II. The MME does not treat certificate-based and pre-shared key-based solution differently. The use of the certificate-based and pre-shared key solutions is specified in Annex D of TS 33.401 [41].
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23.401
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4.3.20.2.2 Attach for RN preconfiguration
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The RN attaches to the E-UTRAN/EPC as a UE at power-up (i.e. the RN shall not include the RN indication in the RRC Connection establishment signalling). The eNodeB treats the RN as a normal UE when performing MME selection.
Because the eNodeB does not indicate that this is a RN in the S1 interface Initial UE message, the MME does not perform any further RN specific actions (e.g. it ignores any indication from the HSS that "this subscription includes a permission to operate as a RN").
The authentication of the "RN acting as an UE" is performed by the MME during this attach procedure, using the information obtained from the HSS.
The MME performs the S-GW and P-GW selection as for a normal UE.
NOTE: It is the responsibility of the HSS operator to ensure that the RN subscription includes an APN configuration that ensures that the RN subscription cannot be used for other purposes, e.g. only a single APN is configured for the use of RNs in phase I, and, that this APN is reserved for RNs only.
The RN retrieves initial RN configuration parameters as user plane traffic, across the SGi reference point, from RN OAM (e.g. list of DeNB cells and selected PLMN).
After this operation is complete, the RN detaches from the network using the normal UE initiated detach procedure, see clause 5.3.8.2.1 and the RN triggers Phase II.
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23.401
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4.3.20.2.3 Attach for RN operation
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To start relay operations, the normal attach procedure, with the following exceptions, is applied:
- The RN and the USIM-RN perform local security operations (e.g. establishment of a secure channel between them) as specified in TS 33.401 [41];
- The RN selects a cell from the list acquired during Phase I;
- The RN establishes an RRC connection with the DeNB, indicating that the connection is for a RN;
- The DeNB is aware of the MMEs that support RN functionality. In all cases when the RN indication is received, the DeNB shall ensure that the current or (re)selected MME supports RN functionality;
NOTE 1: The RN follows normal UE behaviour, e.g. the RN's NAS may use either an IMSI or a GUTI. Also, the RN's NAS may or may not provide an S-TMSI to the RN's AS, and hence, the RRCConnectionRequest may either contain an S-TMSI or a random value.
- In the S1 interface Initial UE Message, the DeNB sends the RN indication to the MME. This message also carries the IP address of the S‑GW/P-GW function embedded in the DeNB;
- The subscription data supplied to the MME by the HSS for USIM-RN includes an indication that the subscription is permitted to be used by a RN.
- If the S1 interface Initial UE Message indicates that this is a RN, but the subscription data does not indicate that the subscription includes a permission to operate as a RN, then the MME shall reject the NAS procedure (e.g. Attach Request, Tracking Area Update Request, Service Request, etc) with an appropriate cause value (e.g. one that avoids retries on this PLMN yet does not harm a RN that has unexpectedly performed PLMN reselection).
NOTE 2: It is anticipated that the MME checks that the HPLMN of the USIM-RN is authorised to attach RNs to this MME.
- The MME and RN perform the normal EPS Authentication procedures.
- MME (RN) selects the S-GW/P-GW in DeNB for the RN based on the IP address included in the Initial UE Message (i.e. all GW selection and APN related procedures are bypassed during this phase). The MME performs S11 interface signalling with the S-GW/P-GW located in the DeNB;
- The MME accepts the attach procedure and sets up an S1 context with the DeNB.
When relay function is enabled, MMEs in a pool should all have the same relaying function capability in order to have consistent support for functions such as redundancy, load balancing.
Figure 4.3.20.2-1: RN attach procedure
The detach procedure for the RN is the same as the normal UE detach procedure, though the RN should ensure that no UE is connected to the RN cells before detaching. It is up to RN implementation how it ensures no UE is connected.
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4.3.20.3 DeNB E-RAB activation/modification
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This procedure is used by the DeNB to change the EPS bearer allocation for the RN. The procedure is the same as the normal network-initiated bearer activation/modification procedure with the exception that the S-GW/P‑GW functionality (steps 1 and 6) is performed by the DeNB.
Figure 4.3.20.3-1: DeNB-initiated bearer activation/modification procedure
NOTE: It is up to implementation if and when the DeNB sets up and modifies EPS bearers for the RN, in addition to the initial bearer set up procedures at Attach.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.21 Core Network assisted eNodeB parameters tuning
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.21.1 CN Assistance Information
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Core Network assisted eNodeB parameters tuning aids the eNodeB to minimize the UE state transitions and achieve optimum network behaviour. How the eNodeB uses the Core Network assistance information is not in scope of this specification and is implementation specific.
Core Network assistance information may be derived by the MME per UE in the MME based on collection of UE behaviour statistics or other available information about the expected UE behaviour (such as subscribed APN, IMSI ranges or other subscription information). If the HSS provides the Communication Pattern (CP) parameters (see TS 23.682 [74]) within the subscription profile information, then the MME may use the CP parameters for selecting the CN assisted eNodeB parameters. The CP parameters received from the HSS are used by the MME as input to derive the CN assisted eNodeB parameter values. For the case of statistics-based Core Network assistance information collection, this may be enabled based on local configuration (e.g. subscribed APN, IMSI ranges or other subscription information). This information provides the eNodeB with a way to understand the UE behaviour for these aspects:
- "Expected UE activity behaviour", i.e. the expected pattern of the UE's changes between ECM-CONNECTED and ECM-IDLE states. This may be derived e.g. from statistical information or from subscription information.
- "Expected HO interval", i.e. the expected time interval between inter-eNodeB handovers. This may be derived e.g. from statistical information or from subscription information. The "Expected HO interval" parameter is not based on subscription information. Highly mobile UEs may have the ECM-CONNECTED state reduced to reduce handover signalling, unless the activity data do not justify that, as reduced handover signalling would be outweighed by more Service Request signalling).
- "UE Differentiation Information" including the Communication Pattern parameters (see TS 23.682 [74]) to support Uu operation optimisation for NB-IoT UE differentiation.
The respective signalling to support this feature is specified in TS 36.413 [36]. The cases where the Traffic Profile (see see TS 23.682 [74]) is not used are described in clauses 5.3.4B.2 and 5.3.4B.3.
The MME decides when to send this information to the eNodeB as "Expected UE behaviour" carried in S1-AP signalling over the S1-MME interface as per procedure documented in clause 4.3.21.3.
NOTE 1: The calculation of the Core Network assistance information, i.e. the algorithms used and related criteria, and the decision when it is considered suitable and stable to send to the eNodeB are vendor specific. Unreliable information should not be provided to the eNodeB as it may drive undesirable system effects.
NOTE 2: It is recommended the MME or, depending on where this assessment is performed, the eNodeB, can consider the average times in the ECM-CONNECTED and ECM-IDLE states an accurate representation of the traffic patterns if the average time in ECM-CONNECTED mode is short enough to assume the UE is generally actively transmitting and/or receiving data while in ECM-CONNECTED state.
NOTE 3: When there are multiple overlapping CP parameter sets received from the HSS for one UE, then the MME considers a merge per CP parameter when deriving the CN assisted eNodeB parameters, e.g. based on the Scheduled communication time and/or Communication duration time parameters. A conflict on the Stationary Indication parameter can be resolved by considering the UE as "mobile".
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23.401
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4.3.21.2 Void
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23.401
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4.3.21.3 Core Network Assistance Procedures
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The MME provides CN assistance information to the eNodeB if available, during the setup of the S1 signalling connection (e.g., Attach, Service Request).
The following figure is a high level description of the transfer of information from an MME to eNodeB during a service request procedure.
Figure 4.3.21.3-1: Core Network assisted eNodeB parameters tuning
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23.401
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4.3.21.4 Wake Up Signal Assistance
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23.401
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4.3.21.4.1 General
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The RAN and UE may use a Wake Up Signal (WUS) to reduce the UE's idle mode power consumption. The RAN sends the WUS shortly before the UE's paging occasion. The WUS feature enables UEs to determine that in the paging occasions immediately following their WUS occasion they will not be paged if their WUS is not transmitted, or that they might be paged if their WUS is transmitted (see TS 36.304 [34]).
To avoid waking up UEs due to an MME paging other UEs across multiple cells (e.g. due to frequent UE mobility and/or for low paging latency services such as VoLTE), the use of WUS by the eNodeB and the UE is restricted to the last used cell, i.e. the cell in which the UE's RRC connection was last released. To support this:
a) WUS-capable eNodeBs should provide the Recommended Cells for Paging IE in the Information On Recommended Cells And eNodeBs For Paging IE (see TS 36.413 [36]) to the MME in the S1 UE Context Release Complete or UE Context Suspend Request messages;
b) if received during the last S1 UE Context Release Complete or UE Context Suspend Request message, the MME provides (without modification) the Recommended Cells for Paging as Assistance Data for Recommended Cells IE in the S1-AP Paging message to the RAN (see also TS 36.413 [36]); and
c) the MME shall delete (or mark as invalid) the Information On Recommended Cells And eNodeBs For Paging when a new S1-AP association is established for the UE.
In the S1-AP Paging message, the last used cell ID is sent in the Assistance Data for Recommended Cells IE in the Assistance Data for Paging IE (see TS 36.413 [36]). When receiving an S1-AP Paging message for a WUS-capable UE that also includes the Assistance Data for Recommended Cells IE then a WUS-capable eNodeB shall only broadcast the WUS on the cell that matches the last used cell ID.
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23.401
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4.3.21.4.2 Group Wake Up Signal
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To support the Group Wake Up Signal feature, the WUS Assistance Information is used by the eNodeB to help determine the WUS group used when paging the UE (see TS 36.300 [5]).
The content of the WUS Assistance Information consists of the paging probability information. The paging probability information provides a metric on the probability of a UE receiving a paging message based on, e.g., statistical information.
The UE may in the Attach Request message provide its capability to support WUS Assistance Information. If WUS Assistance Information is supported, then the UE in the Attach Request or Tracking Area Update message may provide the additional UE paging probability information. The MME may use the UE provided paging probability, local configuration and/or previous statistical information for the UE, when determining the WUS Assistance Information. If the UE supports WUS Assistance Information, the MME may assign WUS Assistance Information to the UE, even when the UE has not provided the additional UE paging probability information.
If the MME has determined WUS Assistance Information for the UE, the MME provides it to the UE in every Attach Accept and/or Tracking Area Update message. The MME stores the WUS Assistance Information parameter in the MM context and provides it to the eNodeB when paging the UE.
UE and MME shall not include WUS Assistance Information in Emergency Attach Request/Attach Accept and in Tracking Area Update/Tracking Area Update Accept messages if the UE has an active emergency PDN connection.
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23.401
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4.3.22 UE Power Saving Mode
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A UE may adopt a PSM that is described in TS 23.682 [74]. If a UE is capable of adopting a PSM and it wants to use the PSM it shall request an Active Time value and may request a Periodic TAU/RAU Timer value during every Attach and TAU procedures, which are handled as described in TS 23.682 [74]. The UE shall not request a Periodic TAU/RAU Timer value if it is not requesting an Active Time value. The network shall not allocate an Active Time value if the UE has not requested it.
PSM has no support in the CS domain on the network side.
NOTE 1: When the PSM is activated the UE might not be available for paging of Mobile Terminated CS services even though the UE is registered in the CS domain.
NOTE 2: The Attach and TAU procedures of this specification are not showing the details of the Periodic TAU Time and Active Time negotiation, i.e. are not showing the related IEs.
If the network allocates an Active Time value, the UE and the MME starts the Active timer (see clause 4.3.5.2) with the Active Time value allocated by the network when transitioning from ECM_CONNECTED to ECM_IDLE. The UE shall stop the Active timer, if running, when a transition to ECM_CONNECTED mode is made. When the Active timer expires, the UE deactivates its Access Stratrum functions and enters PSM. In PSM, due to deactivation of Access Stratum functions, the UE stops all idle mode procedures, but continues to run any NAS timers that may apply, e.g. the periodic TAU timer. The UE shall resume Access Stratum functions and idle mode procedures before the periodic TAU timer expires for performing the periodic TAU procedure as applicable. The UE may resume idle mode procedures and Access Stratum functions any time while in PSM, e.g. for mobile originated communications. Any timers and conditions that remain valid during power-off, e.g. for NAS-level back-off, apply in the same way during PSM.
When the Active timer expires for the UE, the MME knows that the UE entered PSM and is not available for paging. The MME handles availability for paging as detailed in clause 4.3.5.2.
On UE side the PSM complies with some substates of EMM_REGISTERED, as specified in TS 24.301 [46]. The MME considers the UE to be EMM_REGISTERED, but not reachable. The UE's Access Stratum functions are considered as deactivated during PSM.
For mobile terminated data while a UE is in PSM, the functions for High latency communication may be used as described in clause 4.3.17.7.
When the UE has bearers for emergency services, the UE shall not apply PSM.
When the UE is attached for RLOS services, the UE shall not apply PSM.
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23.401
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4.3.23 Access network selection and traffic steering based on RAN-assisted WLAN interworking
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As described in TS 36.300 [5], TS 36.304 [34], TS 36.331 [37] and TS 25.331 [33], UTRAN and E-UTRAN may provide RAN assistance parameters to the UE via RRC signalling. The RAN assistance parameters may e.g. include E-UTRAN signal strength and quality thresholds, WLAN channel utilization thresholds, WLAN backhaul data rate thresholds, a list of WLAN identifiers and Offload Preference Indicator (OPI). The UE uses the RAN assistance parameters to perform access network selection and traffic steering decisions between 3GPP access and WLAN using procedures defined in TS 36.304 [34] or using ANDSF policies defined in TS 23.402 [2]. Co-existence between the procedures defined in TS 36.304 [34] and ANDSF policies is described in TS 23.402 [2].
For traffic steering decisions using procedures defined in TS 36.304 [34] the MME may provide information to the UE indicating which PDN Connection can be offloaded to WLAN and which PDN Connection shall not be offloaded to WLAN. When provided by the MME, this indication is provided in NAS signalling on a per PDN Connection basis when a PDN Connection is established. The MME may provide a per-RAT indication for the PDN connection, e.g. if the indication is different for UTRAN and for E-UTRAN. If the MME provides a single indication, the UE shall apply such indication both to E-UTRAN and UTRAN.
Traffic steering decisions using procedures defined in TS 36.304 [34] are not applicable to non-seamless WLAN offload (see TS 23.402 [2] for the definition of non-seamless WLAN offload).
In order for the operator to allow/prohibit WLAN offloading on per user and per APN basis, subscription data in the HSS may be configured to indicate if WLAN offload is allowed or prohibited for an APN.
The MME determines the WLAN offloading permissions for the UE and PDN Connection as described below:
- The MME determines the offloadability of a PDN Connection based on subscription data and locally configured policy (e.g. for roaming users or when the subscription data does not include any WLAN offloadability indication).
- When the UE establishes a new PDN Connection, the MME may indicate whether this PDN Connection is offloadable or not offloadable to WLAN.
- The MME may provide an updated WLAN offloadability indication of a PDN Connection to the UE. This may be initiated by HSS as part of the Insert Subscriber Data procedure as described in clause 5.3.9.2. It can also be initiated by the MME by initiating steps 4 to 7 of the Bearer Modification Procedure in clause 5.4.3, Figure 5.4.3-1 or by adding the WLAN offloadability indication to a session management NAS message sent to the UE as part of an existing procedure. The MME shall not trigger signalling to an ECM-IDLE UE solely for the purpose of updating the WLAN offloadability indication.
When the UE applies the procedures defined in TS 36.304 [34] and TS 25.304 [12], if the UE has Local Operating Environment Information (LOEI), as defined in TS 23.261 [54], the UE shall consider the RAN rules in combination with the non-radio related aspects of LOEI, and shall give priority to LOEI if it indicates WLAN is not acceptable for non-radio related reasons. For example, if the active RAN rule indicates that traffic shall be moved to WLAN access, but the LOEI in the UE indicates that WLAN access is unacceptable due to non-radio related causes (e.g. due to authentication issues, low battery power, etc.), the UE shall not move the traffic to WLAN.
When the UE applies the procedures defined in TS 36.304 [34], the UE takes into account the WLAN offloadability indication from MME to perform handover between 3GPP access and WLAN access using the handover procedures described in TS 23.402 [2].
When the UE receives a WLAN offloadability indication from the network for a PDN connection the UE stores it for the lifetime of that PDN Connection and updates it if a new value is received from the network. The UE shall apply the latest indication previously received for the PDN Connection.
The indication of whether a PDN connection is offloadable or not offloadable should be passed from the source to the target serving node in mobility management procedures from a MME to a MME/SGSN. This allows the target SGSN/MME to learn the indication previously provided to the UE and to decide the need for providing an updated indication to the UE.
4.3.23a Access network selection and traffic steering based on RAN-Controlled WLAN interworking
As described in TS 36.300 [5] E-UTRAN may support RAN-Controlled WLAN interworking (RCLWI) for controlling traffic steering between E-UTRAN and WLAN for UEs in RRC_CONNECTED. When E-UTRAN sends an "offload" command to the UE, the UE passes an indication to the upper layers indicating that traffic steering to/from WLAN is needed. The upper layers determine to initiate traffic steering to/from WLAN based on the UE capability and the configuration information that has received from NAS layer indicating which PDN connections are offloadable. When the UE receives the "offload" command from the EUTRAN, the UE shall perform handover to WLAN only the PDN connections that have been authorized for offloading.
The NAS level indication about "offloadability" of PDN connections is defined in clause 4.3.23.
The UE uses the RCLWI procedures to perform access network selection and traffic steering decisions between 3GPP access and WLAN or using ANDSF policies defined in TS 23.402 [2]. Co-existence between the procedures defined for RCLWI, ANDSF policies and user preference is described in TS 23.402 [2].
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23.401
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4.3.24 RAN user plane congestion management function
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23.401
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4.3.24.1 General
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The user plane congestion management function addresses how the system can effectively mitigate RAN user plane congestion in order to reduce the negative impact on the perceived service quality. The congestion mitigation measures include traffic prioritization, traffic reduction and limitation of traffic, and shall be able to manage user plane traffic across a range of variables including the user's subscription, the type of application, and the type of content. Congestion mitigation can be performed in the RAN or in the CN, or in a combined way both in the RAN and in the CN.
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23.401
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4.3.24.2 RAN user plane congestion mitigation in the RAN
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Editor's note: Text to be added depending on the outcome of the UPCON study.
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23.401
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4.3.24.3 RAN user plane congestion mitigation in the CN
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RAN user plane congestion mitigation in the CN uses RAN OAM information, collected by the RAN Congestion Awareness Function (RCAF), to detect congestion. The RAN Congestion Awareness Function is further described in clause 4.4.12. This functionality is applicable only in the case of UTRAN/E-UTRAN accesses.
NOTE 1: The criteria used for detection of RAN user plane congestion (including detection of congestion abatement) are outside the scope of 3GPP specifications.
NOTE 2: The interface to the RAN's OAM system is not standardized.
The RCAF can transfer RAN user plane congestion information (RUCI) to the PCRF over the Np reference point in order to mitigate the congestion by measures selected by the PCRF, as specified in TS 23.203 [6]. Decisions to apply congestion mitigation measures may take into account operator policies and subscriber information and all additional available IP-CAN session information.
Different mechanisms and mitigation actions applicable as described in TS 23.203 [6] in order to mitigate RAN User Plane Congestion. Those mechanisms include e.g. service/application gating, service/application bandwidth limitation, deferring of services.
NOTE 3: Co-existence between congestion mitigation in RAN and CN can be assured by appropriate network configuration of applicable policies for congestion mitigation, as well as related RAN parameter alignment/tuning, such as tuning of parameters for e.g., load balancing, carrier aggregation, co-ordinated multipoint, dual connectivity. This parameter alignment/tuning is not further specified.
NOTE 4: A condition leading to interoperability issues which may lead to suboptimal situation is that the time scales for actions of congestion mitigation in RAN and in CN are of comparable duration. Therefore, congestion mitigation in RAN and CN cannot have comparable time scales, otherwise interoperability is affected.
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23.401
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4.3.25 Dedicated Core Networks (DCNs)
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23.401
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4.3.25.1 General
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This feature enables an operator to deploy multiple DCNs within a PLMN with each DCN consisting of one or multiple CN nodes. Each DCN may be dedicated to serve specific type(s) of subscriber. This is an optional feature and enables DCNs to be deployed for one or multiple RATs (e.g. GERAN, UTRAN, E-UTRAN, WB-E-UTRAN and NB-IoT). There can be several motivations for deploying DCNs, e.g. to provide DCNs with specific characteristics/functions or scaling, to isolate specific UEs or subscribers (e.g. M2M subscribers, subscribers belonging to a specific enterprise or separate administrative domain, etc.).
A DCN comprises of one or more MME/SGSN and it may comprise of one or more SGW/PDN GW/PCRF. This feature enables subscribers to be allocated to and served by a DCN based on subscription information ("UE Usage Type"). The feature in this clause handles both DCN selections without any specific UE functionality, i.e. it works also with UEs of earlier releases and UE assisted DCN selection.
The main specific functions are for routing and maintaining UEs in their respective DCN. The following deployment scenarios are supported for DCN:
- DCNs may be deployed to support one RAT only, (e.g. only dedicated MMEs are deployed to support E-UTRAN and dedicated SGSNs are not deployed), to support multiple RATs, or to support all RATs.
- Networks deploying DCNs may have a default DCN, which is managing UEs for which a DCN is not available or if sufficient information is not available to assign a UE to a DCN. One or multiple DCNs may be deployed together with a default DCN that all share the same RAN.
- The architecture supports scenarios where the DCN is only deployed in a part of the PLMN e.g. only for one RAT or only in a part of the PLMN area. Such heterogeneous or partial deployment of DCNs may, depending on operator deployment and configuration, result in service with different characteristics or functionality, depending on whether the UE is inside or outside the service area or RAT that supports the DCN.
NOTE 1: Heterogeneous or partial deployment of DCNs may result in increased occurrence of UEs first being served by a CN node in the default DCN and then being redirected to a CN node in the DCN that serves the UE when the UE moves from areas outside of DCN coverage to an area of DCN coverage. It may also result in an increased re-attach rate in the network. As this has impacts on the required capacity of the default CN nodes deployed at edge of DCN coverage, it is not recommended to deploy DCNs heterogeneously or partially.
- Even if the DCN is not deployed to serve a particular RAT or service area of PLMN, the UE in that RAT or service area may still be served by a PDN GW from the DCN.
High level overview for supporting DCNs is provided below. Details are captured in appropriate clauses of this specification, TS 23.060 [7] and TS 23.236 [30].
- An optional subscription information parameter ("UE Usage Type") is used in the selection of a DCN. An operator configures which of his DCN(s) serves which UE Usage Type(s). The HSS provides the "UE Usage Type" value in the subscription information of the UE to the MME/SGSN. Both standardized and operator specific values for UE Usage Type are possible.
- The serving network selects the DCN based on the operator configured (UE Usage Type to DCN) mapping, other locally configured operator's policies and the UE related context information available at the serving network, e.g. information about roaming. UEs with different UE Usage Type values may be served by the same DCN. Moreover, UEs that share the same UE Usage Type value may be served by different DCNs.
- If the configuration shows no DCN for the specific "UE Usage Type" value in the subscription information, then the serving MME/SGSN serves the UE by the default DCN or selects a DCN using serving operator specific policies.
- Some subscribers may be configured without "UE Usage Type" value. In this case, the MME/SGSN may select the DCN that serves the UE using locally configured operator's policies and the UE related context information available at the serving network (other than UE provided DCN-ID). The MME/SGSN performs procedures described in clauses 5.19.1 and 5.19.2.
- The "UE Usage Type" is associated with the UE (describing its usage characteristic), i.e. there is only one UE Usage Type" per UE subscription.
- For each DCN, one or more CN nodes may be configured as part of a pool.
- For MME, the MMEGI(s) identifies a DCN within the PLMN. For SGSNs, a group identifier(s) identifies a DCN within the PLMN. That is, the group of SGSNs that belong to a DCN within a PLMN. This identifier may have the same format as NRI (e.g. an NRI value that does not identify a specific SGSN node in the serving area) in which case it is called "Null-NRI" or it may have a format independent of NRI, in which case it is called "SGSN Group ID". The "Null-NRI" or "SGSN Group ID" is provided by an SGSN to RAN which triggers the NNSF procedure to select an SGSN from the group of SGSNs corresponding to the Null-NRI/SGSN Group ID (see clause 5.19.1).
NOTE 2: SGSN Group IDs enable to handle deployment scenarios where in a service area all NRI values are allocated to SGSNs and hence no NRI value remains that can be used as Null-NRI.
- The dedicated MME/SGSN that serves the UE selects a dedicated S-GW and P-GW based on UE Usage Type.
- At initial access to the network if sufficient information is not available for RAN to select a specific DCN, the RAN may selects a CN node from the default DCN. A redirection to another DCN may then be required.
- To redirect a UE from one DCN to a different DCN, the redirection procedure via RAN, described in clause 5.19.1, is used to forward the NAS message of the UE to the target DCN.
- All selection functions are aware of DCN(s), including the network node selection function (NNSF) of RAN nodes, for selecting and maintaining the appropriate DCN for the UEs.
4.3.25.1a UE assisted Dedicated Core Network selection
This feature is to reduce the need for DECOR reroute by using an indication (DCN-ID) sent from the UE and used by RAN to select the correct DCN. The DCN-ID shall be assigned to the UE by the serving PLMN and is stored in the UE per PLMN ID. Both standardized and operator specific values for DCN-ID are possible. The UE shall use the PLMN specific DCN-ID whenever a PLMN specific DCN-ID is stored for the target PLMN.
The HPLMN may provision the UE with a single default standardized DCN-ID which shall be used by the UE only if the UE has no PLMN specific DCN-ID of the target PLMN. When a UE configuration is changed with a new default standardized DCN-ID, the UE shall delete all stored PLMN specific DCN-IDs.
The UE provides the DCN-ID to RAN at registration to a new location in the network, i.e. in Attach, TAU and RAU. RAN selects serving node (MME or SGSN) based on the DCN-ID provided by the UE and configuration in RAN. For E-UTRAN the eNodeB is configured with DCNs supported by the connected MMEs at the setup of the S1 connection. For UTRAN and GERAN the BSS/RNC is configured with the DCNs supported in the connected SGSN via O&M. Both standardized DCN-IDs and PLMN specific DCN-IDs can in the RAN configuration be assigned to the same network. If information provided by the UE (e.g. GUTI, NRI, etc.) indicates a node (MME or SGSN) for attach/TAU/RAU and a serving node (MME or SGSN) corresponding to the UE information can be found by the RAN node, the normal node selection shall take precedence over the selection based on DCN-ID. At registration the MME/SGSN may check if the correct DCN is selected. The check is performed as specified in clause 4.3.25.1. If the MME/SGSN concludes that the selected DCN is not the correct DCN, a DECOR reroute is performed and the SGSN/MME in the new DCN assigns a new DCN-ID to the UE. The serving MME/SGSN can also assign a new DCN-ID to the UE if e.g. the DCN-ID in the UE has become obsolete or when the UE Usage Type has been updated in the subscription information leading to a change of DCN. This is performed as part of the GUTI Reallocation procedure.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.25.2 Considerations for Roaming
|
In the case of roaming, if the HPLMN of the visiting UE does not support DCNs, i.e. doesn't provide the UE Usage Type, the serving MME/SGSN may select the DCN that serves the UE using operator specific policies based on other subscription or UE provided information.
In the case of roaming, if the HPLMN provides the UE Usage Type parameter to the VPLMN, this parameter is provided irrespective of its value (standardized or operator specific). The handling of the UE Usage Type parameter in the VPLMN is based on operator policies, e.g. roaming agreements.
If the UE assisted DCN selection feature is supported:
- If the UE has a DCN-ID for the VPLMN the UE shall send that PLMN specific DCN-ID to the RAN, and
- If the UE has no PLMN specific DCN-ID for this VPLMN and if the UE has a pre-provisioned default standardized DCN-ID it shall send the pre-provisioned default standardized DCN-ID to the RAN.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.25.3 Considerations for Network Sharing
|
If the network supports the MOCN configuration for network sharing (see TS 23.251 [24]), each network sharing operator has separate CN(s). Mechanisms for selection of serving operator for supporting and non-supporting UEs are defined in TS 23.251 [24]. Each of the sharing operators may deploy one or more DCNs.
If Selected PLMN information is provided by the UE, the RAN selects the CN operator based on this provided information and then DECOR rerouting may, if needed, be initiated within the CN of the selected operator. If the UE assisted DCN selection feature is supported and both the Selected PLMN information and DCN-ID is provided by the UE, the RAN first selects the CN operator followed by selection of a DCN supported by the selected CN operator.
If Selected PLMN information is not provided by the UE (may only happen in GERAN and UTRAN), the network initiates MOCN redirection, including CS/PS coordination, to select a CN operator that can serve the UE. After this, DECOR rerouting is initiated if needed. The serving node in the selected DCN ends the MOCN redirection. If the UE assisted DCN selection feature is supported and Selected PLMN information is not provided by the UE, the network initiates CN operator selection and after the CN operator selection is concluded the DCN is selected based on the UE provided DCN-ID. As the PLMN information included in the RAI is the Common PLMN (refer to TS 23.251 [24]), which does not reflect the selected CN operator, the network may also return the PLMN ID of the selected CN operator. When the UE receives the NAS Accept message, the UE associates the DCN-ID with both the PLMN ID of the selected CN operator and the Common PLMN IDs.
The functions for redirecting or maintaining UEs in specific DCNs are configured to work within the CNs of the same operator.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.26 Support for Monitoring Events
|
The Monitoring Events feature is intended for monitoring of specific events in 3GPP system and making such monitoring event information available via the Service Capability Exposure Function (SCEF). The architecture and related functions to support Monitoring Events are defined in TS 23.682 [74].
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.27 Paging Enhancements
| |
495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.27.1 Paging for Enhanced Coverage
|
Support of UEs in Enhanced Coverage is specified in TS 36.300 [5].
Whenever S1 is released and Information for Enhanced Coverage is available for the UE, the eNodeB sends it to the MME as described in clause 5.3.5.
The MME stores the received Information for Enhanced Coverage and includes it in every subsequent Paging message for all eNodeBs selected by the MME for paging. If Enhanced Coverage is restricted for the UE as described in clause 4.3.28, the MME sends the Enhanced Coverage Restricted parameter as defined in TS 36.413 [36].
4.3.27a Restriction of use of Enhanced Coverage for voice centric UE
Support of UEs in Enhanced Coverage is specified in TS 36.300 [5].
If the UE's usage setting is "voice centric" as defined in TS 23.221 [27], it shall not operate in CE mode B.
If the UE supports CE mode B and UE's usage setting is set to "voice centric" in the Attach or TAU request message then the MME shall indicate to eNodeB that CE mode B is restricted. If the UE supports CE mode B and UE's usage setting is set to "data centric" in the Attach or TAU request message then, based on operator's policy and the Enhanced Coverage Restricted parameter (see clause 4.3.28), the MME shall indicate to eNodeB that CE mode B is not restricted.
The MME keeps the CE mode B Restricted parameter in the MM Context. The MME shall send the CE mode B Restricted parameter to the eNodeB via S1 signalling indicating whether the UE is "restricted" or "not restricted" for the use of CE mode B, e.g. in PAGING, INITIAL CONTEXT SETUP REQUEST, HANDOVER REQUEST, PATH SWITCH REQUEST ACKNOWLEDGE, CONNECTION ESTABLISHMENT INDICATION, and DOWNLINK NAS TRANSPORT message carrying the TAU ACCEPT message.
If the UE supports CE mode B and the CE mode B Restricted parameter stored in the MME's MM context is set to "not restricted", the MME shall use the extended NAS timer settings for the UE as specified in TS 24.301 [46].
4.3.27b Enhanced Coverage for data centric UEs
The support for UEs in Enhanced Coverage is specified in TS 36.300 [5].
The IMS impacts for data centric UEs in Enhanced Coverage is specified in Annex E of TS 23.228 [52].
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.28 Restriction of use of Enhanced Coverage
|
Support of UEs in Enhanced Coverage is specified in TS 36.300 [5].
The usage of Enhanced Coverage may require use of extensive resources (e.g. radio and signalling resources) from the network. This feature enables the operator to prevent specific subscribers from using Enhanced Coverage.
The UE indicates its capability of support for restriction of use of Enhanced Coverage in Attach and TAU procedure for the RAT it is camping on to the MME. MME receives Enhanced Coverage Restricted parameter from the HSS. This parameter is kept as part of subscription data in the HSS and specifies per PLMN whether the enhanced coverage functionality is restricted or not for the UE. For roaming UEs, if HSS doesn't provide any Enhanced Coverage Restricted parameter or the provided Enhanced Coverage Restricted parameter is in conflict with the roaming agreement, the MME uses default Enhanced Coverage Restricted parameter locally configured in the VPLMN based on the roaming agreement with the subscriber's HPLMN. The UE shall assume that restriction for use of Enhanced Coverage is same in the equivalent PLMNs. If the UE includes the support for restriction of use of Enhanced Coverage, MME sends Enhanced Coverage Restricted parameter to the UE in the Attach/TAU Accept message. The UE shall use the value of Enhanced Coverage Restricted parameter to determine if enhanced coverage feature is restricted or not.
NOTE: How this parameter is used by UE at AS layer is defined in the RAN specification.
The UE assumes Enhanced Coverage is allowed unless explicitly restricted by the network for a PLMN. NB-IoT cells also broadcast the support of restriction of use of Enhanced Coverage as defined in TS 36.331 [37]).
If the MME has sent the Enhanced Coverage Restricted parameter to the UE, the MME provides an Enhanced Coverage Restricted parameter to the eNodeB via S1 signalling during paging, and whenever the UE context is established in RAN, e.g. during service request procedure, attach procedure, and TAU procedure.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.29 3GPP PS Data Off
| |
495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.29.1 General
|
This feature, when activated by the user, prevents transport via 3GPP access of all IP packets, Ethernet data and non-IP data except for those related to 3GPP PS Data Off Exempt Services. The 3GPP PS Data Off Exempt Services are a set of operator services, defined in TS 23.221 [27], that are the only allowed services when the 3GPP PS Data Off feature has been activated by the user.
UEs may be configured with up to two lists of 3GPP PS Data Off Exempt Services and the list(s) are provided to the UEs by HPLMN via Device Management or UICC provisioning. When the UE is configured with two lists, one list is valid for the UEs camping in the home PLMN and the other list is valid for any VPLMN the UE is roaming in. When the UE is configured with a single list, without an indication to which PLMNs the list is applicable, then this list is valid for the home PLMN and any PLMN the UE is roaming in.
NOTE 1: The operator needs to ensure coordinated lists of 3GPP Data Off Exempt Services provisioned in the UE and configured in the network.
The UE discovers whether a PDN GW supports 3GPP PS Data Off feature at initial attach and during the establishment of a PDN connection via the presence of the 3GPP PS Data Off Support Indication in the Create Session response message.
NOTE 2: When the UE detects that the PDN GW does not support 3GPP PS Data Off feature, how the UE reacts to non-exempt services MT requests from the network is implementation dependent.
The UE shall report its 3GPP PS Data Off status in PCO (Protocol Configuration Option) to PDN GW during Initial Attach procedure as described in clause 5.3.2.1 and UE requested PDN connectivity procedure as described in clause 5.10.2.
NOTE 3: This also covers scenarios when the user activates/deactivates 3GPP PS Data Off while connected via WLAN access only, and then a handover to 3GPP access occurs.
If 3GPP PS Data Off is activated, the UE prevents the sending of uplink IP packets, Ethernet data and non-IP data except for those related to 3GPP PS Data Off Exempt Services, based on the pre-configured list of Data Off Exempt Services.
For those PDN GWs that indicated support for the 3GPP PS Data Off feature during PDN connection setup and at Initial Attach, the UE shall report immediately a change of its 3GPP PS Data Off status in PCO by using Bearer Resource Modification procedure as described in clause 5.4.5, this also applies to the scenario of inter-RAT mobility procedure to E-UTRAN and also to scenarios where the 3GPP PS Data Off status is changed when the session management back-off timer is running as specified in clause 4.3.7.4.2. If the UE has not received any 3GPP PS Data Off Support Indication during the establishment of the PDN connection, it shall not report any change of its 3GPP PS Data Off Status for this PDN connection.
The additional behaviour of the PDN GW for 3GPP PS Data Off is controlled by local configuration or policy from the PCRF as defined in TS 23.203 [6].
NOTE 4: For the PDN connection used for IMS services, the 3GPP Data Off Exempt Services are enforced in the IMS domain as specified TS 23.228 [52]. Policies configured in the PDN GW/PCRF need to ensure those services are always allowed when the 3GPP Data Off status of the UE is set to "activated".
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.30 Unlicensed spectrum aggregation (LAA/LWA/LWIP/NR-U)
|
Unlicensed spectrum aggregation in EPS can use either LTE Licensed-Assisted Access (LAA) that is using the Carrier Aggregation (CA) RAN configuration defined in TS 36.300 [5], or LWA/LWIP aggregation using WLAN or NR-U as secondary RAT that is using the Dual Connectivity architecture defined in clause 4.3.2a and TS 36.300 [5].
If the UE has Access Restriction for Unlicensed Spectrum in the form of LAA, LWA/LWIP, or NR-U (either signalled from the HSS, or, locally generated by VPLMN policy in the MME) the MME signals this to the E-UTRAN as part of Handover Restriction List.
An eNodeB supporting aggregation with unlicensed spectrum in the form of LAA, LWA/LWIP, or NR-U checks whether the UE is allowed to use unlicensed spectrum. If the UE is not allowed to use Unlicensed Spectrum, the eNodeB shall not establish dual connectivity or carrier aggregation (CA) with LTE in unlicensed spectrum in the form of LAA, WLAN as a secondary RAT in the form of LWA/LWIP, or NR-U as a secondary RAT.
At inter-RAT handover from GERAN/UTRAN, the Access Restriction for Unlicensed Spectrum is either already in the MME's UE context, or is obtained from the HSS during the subsequent Tracking Area Update procedure (i.e. not from the source SGSN or source RAN). In both inter-RAT handover cases, any Access Restriction for use of Unlicensed Spectrum is then signalled to the E-UTRAN.
NOTE: This signalling of the Access Restriction during the TAU after the inter-RAT handover procedure means that there is a small risk that unlicensed spectrum resources are transiently allocated.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.3.31 Subscription handling for Aerial UEs
|
This clause describes subscription information handling in order to support operating Aerial UE function over E-UTRAN as defined in TS 36.300 [5] and TS 36.331 [37].
The eNodeB supporting Aerial UE function handling uses the per user information supplied by the MME to determine whether or not to allow the UE to use Aerial UE function.
Support of Aerial UE function is stored in the user's subscription information in HSS. HSS transfers this information to the MME via Update Location message during Attach and Tracking Area Update procedures. Home Operator may revoke user's subscription authorisation for operating Aerial UEs at any time.
MME that supports Aerial UE function provides the user's subscription information on Aerial UE authorisation to the eNodeB via the S1 AP Initial Context Setup Request during Attach, Tracking Area Update and Service Request procedures.
For the intra and inter MME S1 based handover (intra RAT) or Inter-RAT handover to E-UTRAN, the Aerial UE subscription information for the user is included in the S1-AP UE Context Modification Request message sent to the target eNodeB after the handover procedure.
For X2-based handover, the Aerial UE subscription information for the user is sent to target eNodeB as follows:
- If the source eNodeB supports Aerial UE function and the user's Aerial UE subscription information is included in the UE context, the source eNodeB shall include the information in the X2-AP Handover Request message to the target eNodeB.
- The MME shall send the Aerial UE subscription information to the target eNodeB in the Path Switch Request Acknowledge message.
If the Aerial UE subscription information has changed, the updated Aerial UE subscription information is included in the S1-AP UE Context Modification Request message sent to the eNodeB.
|
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