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10.10 CAPIF_Access_Control_Policy API
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10.10.1 General
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API description: This API enables the API exposing function to obtain the policy to perform access control on the service API invocations.
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10.10.2 Obtain_Access_Control_Policy operation
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API operation name: Obtain_Access_Control_Policy
Description: Allows obtaining the policy to perform access control on the service API invocations.
Known Consumers: API exposing function.
Inputs: Refer subclause 8.12.2.1.
Outputs: Refer subclause 8.12.2.2.
See subclause 8.12.3 for the details of usage of this API operation.
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10.11 CAPIF_Routing_Info API
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10.11.1 General
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API description: This API enables the API exposing function to obtain the routing information to forward the API invocation to another API exposing function.
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10.11.2 Obtain_Routing_Info operation
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API operation name: Obtain_Routing_Info
Description: Allows obtaining the API routing information.
Known Consumers: API exposing function.
Inputs: Refer subclause 8.27.2.1.
Outputs: Refer subclause 8.27.2.2.
See subclause 8.27.3 for the details of usage of this API operation.
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10.12 CAPIF_API_provider_management API
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10.12.1 General
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API description: This API enables the API Management Function to communicate with the CAPIF core function to register the API provider domain functions as authorized users of the CAPIF functionalities.
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10.12.2 Register_API_Provider operation
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API operation name: Register_API_Provider
Description: Registers the API provider domain functions as authorized users of the CAPIF.
Known Consumers: API Management Function.
Inputs: Refer subclause 8.28.2.1.
Outputs: Refer subclause 8.28.2.2.
See subclause 8.28.3 for the details of usage of this API operation.
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10.12.3 Update_API_Provider operation
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API operation name: Update_API_Provider
Description: Updates registration information of the API provider domain functions.
Known Consumers: API Management Function.
Inputs: Refer subclause 8.29.2.1.
Outputs: Refer subclause 8.29.2.2.
See subclause 8.29.3 for the details of usage of this API operation.
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10.12.4 Deregister_API_Provider operation
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API operation name: Deregister_API_Provider
Description: De-registers the API provider domain functions on the CAPIF core function.
Known Consumers: API Management Function.
Inputs: Refer subclause 8.30.2.1.
Outputs: Refer subclause 8.30.2.2.
See subclause 8.30.3 for the details of usage of this API operation.
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11 API exposing function APIs
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11.1 General
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Table 11.1-1 illustrates the API exposing function APIs.
Table 11.1-1: List of API exposing function APIs
API Name
API Operations
Known Consumer(s)
Communication Type
AEF_Security API
Revoke_Authorization
CAPIF Core Function
Request/ Response
Initiate_Authentication
API Invoker
Request/ Response
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11.2 AEF_Security API
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11.2.1 General
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API description: This API allows CAPIF core function to revoke access to service APIs and API invokers to request the authentication parameters necessary for authentication of the API invoker available with the API exposing function.
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11.2.2 Revoke_Authorization operation
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API operation name: Revoke_Authorization
Description: Revokes API invoker authorization to access service API.
Known Consumers: CAPIF core function.
Inputs: Refer subclause 8.23.2.
Outputs: Refer subclause 8.23.2.
See subclause 8.23.4 for the details of usage of this API operation.
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11.2.3 Initiate_Authentication operation
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API operation name: Initiate_Authentication Description: Authentication between the API invoker and the AEF prior to service API invocation. Known Consumers: API Invoker. Inputs: Refer subclause 8.14.2. Outputs: Refer subclause 8.14.2. See subclause 8.14.3 for the details of usage of this API operation. Annex A (informative): Overview of CAPIF operations Depicted in figure A-1 is the overview of CAPIF operations. CAPIF operations occur between different actors involving the API invoker, the CAPIF core function, the API exposing function, the API publishing function and the API management function, and optionally the resource owner function for RNAA. High level CAPIF interactions between the actors are shown in figure A-1. This figure is only provided for illustration purposes, and does not represent the order of operations. Figure A-1: Overview of CAPIF operations The CAPIF defines the functional entities in subclause 6.3. The CAPIF defines the reference points between the functional entities in subclause 6.4. The following operations require the communication between the CAPIF entities: 1. Publishing service APIs: the API provider utilizes the API publishing function over CAPIF-4 reference point to publish the service APIs on the CAPIF core function, as specified in subclause 8.3 of this specification; 2. Discovering service APIs: the API invoker discovers the service APIs over CAPIF-1/CAPIF-1e reference points, as specified in subclause 8.7 of this specification; 3. API event subscription and notification: the API invoker subscribes to and receive service API event notifications over CAPIF-1/CAPIF-1e reference points, as specified in subclause 8.8 of this specification; 4. Authenticating with CAPIF: the API invoker authenticates itself over CAPIF-1/CAPIF-1e reference points, as specified in subclause 8.10 of this specification; 5. Authorizing with CAPIF: the API invoker obtains service API authorization over CAPIF-1/CAPIF-1e reference points, as specified in subclause 8.11 of this specification. In RNAA scenarios, API authorization is based on the authorization information obtained from the resource owner, as specified in clause 8.31; 6. Topology hiding: the API provider, to hide the topology, utilizes the API exposing function over CAPIF-3 reference point, as specified in subclause 8.13 of this specification; 7. Authenticating the API invoker prior to service API invocation: the API provider, to authenticate the API invoker prior to the service API invocation, utilizes the API exposing function over CAPIF-2/CAPIF-2e and CAPIF-3, as specified in subclause 8.14 of this specification; 8. Authenticating the API invoker upon the service API invocation: the API provider, to authenticate the API invoker upon invocation of the service APIs, utilizes the API exposing function over CAPIF-2/CAPIF-2e and CAPIF-3, as specified in subclause 8.15 of this specification; 9. Authorizing API invoker: the API provider, to authorize the API invoker to access the service APIs, utilizes the API exposing function over CAPIF-2/CAPIF-2e and CAPIF-3, as specified in subclause 8.16 of this specification; 10. Access control: the API provider, to control the access of the service API by the API invoker based on policy or usage limits, - utilizes the API exposing function over CAPIF-2/CAPIF-2e and CAPIF-3, as specified in subclause 8.17 of this specification; or - in a cascaded deployment, utilizes API exposing functions over CAPIF-2/CAPIF-2e, as specified in subclause 8.18 of this specification; 11. Logging service: the API provider, to maintain the log of the API invocations at the CAPIF core function for services such as charging, invocation history, utilizes the API exposing function over CAPIF-3, as specified in subclause 8.19 of this specification; 12. Charging service: the API provider, to facilitate charging of the API invocations, utilizes the API exposing function over CAPIF-3, as specified in subclause 8.20 of this specification; 13. Service monitoring: the API provider, to facilitate monitoring such as API invoker's ID and IP address, utilizes the API management function over CAPIF-5, as specified in subclause 8.21 of this specification; and 14. Auditing: the API provider, for auditing, utilizes the API management function over CAPIF-5, as specified in subclause 8.22 of this specification. Annex B (informative): CAPIF relationship with network exposure aspects of 3GPP systems This annex provides the relationship of CAPIF with network exposure aspects of 3GPP systems. Any system exposing capabilities as service APIs can implement CAPIF. Generic model for CAPIF utilization by service API provider is included. Network exposure aspects of EPS and 5GS are considered for illustration. NOTE: As there are no impacts on CAPIF's relationship with network exposure aspects of 3GPP systems due to deployment of 3rd party trust domain, it is not illustrated in the figures. B.0 CAPIF utilization by service API provider Figure B.0-1 illustrates the service API interaction with the CAPIF for utilizing framework aspects provided by the CAPIF. Figure B.0-1: CAPIF utilization by service API provider The service API aspects of the 3GPP network services and capabilities such as subscriber management, mobility management, transport and other communication services can be exposed for consumption by external 3rd party applications (e.g. API invoker). Framework aspects typically horizontal in nature caters to common functionality such as onboarding, offboarding, publishing, unpublishing, update service API, discovery, authentication, registration, authorization, logging, charging, monitoring, configuration, topology hiding, that are required to provide service APIs to API invokers. Service APIs can utilize the functions of the API provider domain (i.e. API exposing function, API publishing function, API management function) and interfaces CAPIF-3, CAPIF-4 and CAPIF-5 as specified in this specification. The service API exposure function is connected to 3GPP network entity(s) via 3GPP internal interface(s). The API publishing function provides the service API information for publishing to the CAPIF core function. For consuming service API, the API invoker interacts with the service API exposure function via service API interface and CAPIF-2/2e. While the service API interface is responsible for providing service aspects, CAPIF-2/2e supports service API by providing framework aspects such as authentication of the API invoker, authorization verification for the API invoker upon accessing the service API. B.1 CAPIF relationship with 3GPP EPS network exposure B.1.1 General The table B.1.1-1 shows the relationship between CAPIF and EPS network exposure aspects. The details of SCEF and its role in exposing network capabilities of EPS to 3rd party applications are specified in 3GPP TS 23.682 [2] Table B.1.1-1: CAPIF relationship with 3GPP EPS network exposure Aspects CAPIF EPS network exposure Entity providing the APIs to external or 3rd party applications AEF SCEF Entity providing framework related services to the applications (discovery, authentication, authorization, etc) CAPIF core function SCEF Entity representing the external or 3rd party applications API invoker SCS/AS Entity providing framework related services to support the APIs operation and management (publish, policy enforcements, charging) CAPIF core function SCEF Interface/Reference point for exposing network capabilities as APIs CAPIF-2 and CAPIF-2e (Do not include the service specific aspects) T8 Interface/Reference point for exposing framework services as APIs to the applications CAPIF-1 and CAPIF-1e Not specified. (May be via T8) Interface/Reference point for framework services to support the APIs operation and management CAPIF-3, CAPIF-4 and CAPIF-5 Internal to SCEF B.1.2 Deployment models B.1.2.1 General Based on the relationship captured in table B.1.1-1, the following deployment models for CAPIF are possible to enable EPS network exposure. NOTE: The deployment models captured in subclause 7 are possible for the SCEF deployment compliant with CAPIF. Not all deployment models are illustrated in this subclause. B.1.2.2 SCEF implements the CAPIF architecture Figure B.1.2.2-1 illustrates the deployment model where SCEF implements the CAPIF architecture. Figure B.1.2.2-1: SCEF implements the CAPIF architecture The SCEF can implement the functionalities of the CAPIF core function, the API exposing function, the API publishing function and the API management function. According to the CAPIF architecture, CAPIF-2 and CAPIF-2e consist of framework aspects and service specific aspects. The service specific aspects are out of scope of CAPIF. T8 can implement the service specific aspects of CAPIF-2 and CAPIF-2e, and can provide the service APIs exposed by SCEF (AEF) to the SCS/AS (API invoker). The SCEF can additionally provide CAPIF-1 and CAPIF-1e (CAPIF APIs) to the SCS/AS (API invokers). B.1.2.3 SCEF implements the service specific aspect compliant with the CAPIF architecture Figure B.1.2.3-1 illustrates the deployment model where SCEF implements the service specific aspect compliant with the CAPIF architecture. Figure B.1.2.3-1: SCEF implements the service specific aspect compliant with the CAPIF architecture 3GPP EPS can deploy the CAPIF core function along with the SCEF. The SCEF can implement the functionalities of the API provider domain functions. According to the CAPIF architecture, CAPIF-2 and CAPIF-2e consist of framework aspects and service specific aspects. The service specific aspects are out of scope of CAPIF. T8 can implement the service specific aspects of CAPIF-2 and CAPIF-2e, and can provide the service APIs exposed by SCEF (AEF) to the SCS/AS (API invoker). The SCEF can implement the CAPIF-3 reference point/interface to the CAPIF core function. B.1.2.4 Distributed deployment of the SCEF compliant with the CAPIF architecture Figure B.1.2.4-1 illustrates the distributed deployment model where the SCEF implements the service specific aspect compliant with the CAPIF architecture. Figure B.1.2.4-1: Distributed deployment of SCEF compliant with the CAPIF architecture The 3GPP EPS can deploy the CAPIF core function, the SCEF-2 (API exposing function as a gateway) along with the SCEF-1 as illustrated in subclause 7.3. The SCEF can implement the functionalities of API provider domain functions. According to the CAPIF architecture, CAPIF-2 or CAPIF-2e consists of framework aspects and service specific aspects. The service specific aspects are out of scope of the CAPIF. T8 can implement the service specific aspects of CAPIF-2 or CAPIF-2e and can provide the service APIs exposed by the SCEF-2 (AEF as a gateway) to the SCS/AS (API invoker). The SCEF-2 can implement the CAPIF-3 reference point to the CAPIF core function and the SCEF-1 can implement the CAPIF-4 and CAPIF-5 reference points to the CAPIF core function. B.2 CAPIF relationship with 3GPP 5GS network exposure B.2.1 General The table B.2.1-1 shows the relationship between CAPIF and 5GS network exposure aspects. The details of NEF and its role in exposing network capabilities of 5GS to 3rd party applications are specified in 3GPP TS 23.501 [3] and the details of NEF service operations are specified in 3GPP TS 23.502 [4]. Table B.2.1-1: CAPIF relationship with 3GPP 5GS network exposure Aspects CAPIF 5GS network exposure Entity providing the APIs to external or 3rd partyapplications AEF NEF Entity providing framework related services to the applications (discovery, authentication, authorization, etc) CAPIF core function NEF (Not specified yet) Entity representing the external or 3rd party applications API invoker AF Entity providing framework related services to support the APIs operation and management (publish, policy enforcements, charging) CAPIF core function NEF (Not specified yet) Interface/Reference point for exposing network capabilities as APIs CAPIF-2 and CAPIF-2e (Do not include the service specific aspects) Nnef Interface/Reference point for exposing framework services as APIs to the applications CAPIF-1 and CAPIF-1e Nnef (Not specified yet) Interface/Reference point for framework services to support the APIs operation and management CAPIF-3, CAPIF-4 and CAPIF-5 Internal to NEF B.2.2 Deployment models B.2.2.1 General Based on the relationship captured in table B.2.1-1, the following deployment models for CAPIF are possible to enable 5GS network exposure. NOTE: The deployment models captured in subclause 7 are possible for the NEF deployment compliant with CAPIF. Not all deployment models are illustrated in this subclause. B.2.2.2 NEF implements the CAPIF architecture Figure B.2.2.2-1 illustrates the deployment model where the NEF implements the CAPIF architecture. Figure B.2.2.2-1: NEF implements the CAPIF architecture The NEF can implement the functionalities of the CAPIF core function, the API exposing function, the API publishing function and the API management function. According to the CAPIF architecture, CAPIF-2 and CAPIF-2e consist of framework aspects and service specific aspects. The service specific aspects are out of scope of CAPIF. Nnef can implement the service specific aspects of CAPIF-2 and CAPIF-2e, and can provide the service APIs exposed by the NEF (AEF) to the AF (API invoker). The NEF can additionally provide CAPIF-1 and CAPIF-1e (CAPIF APIs) to the AF (API invokers). B.2.2.3 NEF implements the service specific aspect compliant with the CAPIF architecture Figure B.2.2.3-1 illustrates the deployment model where the NEF implements the service specific aspect compliant with the CAPIF architecture. Figure B.2.2.3-1: NEF implements the service specific aspect compliant with the CAPIF architecture 3GPP 5GS can deploy the CAPIF core function along with the NEF. The NEF can implement the functionalities of the API provider domain functions. According to the CAPIF architecture, CAPIF-2 and CAPIF-2e consist of framework aspects and service specific aspects. The service specific aspects are out of scope of CAPIF. Nnef can implement the service specific aspects of CAPIF-2 and CAPIF-2e, and can provide the service APIs exposed by NEF (AEF) to the AF (API invoker). The NEF can implement the CAPIF-3 reference point/interface to the CAPIF core function. B.2.2.4 Distributed deployment of the NEF compliant with the CAPIF architecture Figure B.2.2.4-1 illustrates the distributed deployment model where the NEF implements the service specific aspect compliant with the CAPIF architecture. Figure B.2.2.4-1: Distributed deployment of NEF compliant with the CAPIF architecture The 3GPP 5GS can deploy the CAPIF core function, the NEF-2 (API exposing function as a gateway) along with the NEF-1 as illustrated in subclause 7.3. The NEF can implement the functionalities of API provider domain functions. According to the CAPIF architecture, CAPIF-2 or CAPIF-2e consists of framework aspects and service specific aspects. The service specific aspects are out of scope of the CAPIF. Nnef can implement the service specific aspects of CAPIF-2 and CAPIF-2 or CAPIF-2e can provide the service APIs exposed by the NEF-2 (AEF as a gateway) to the AF (API invoker). The NEF-2 (AEF) can implement the CAPIF-3 reference point to the CAPIF core function and the NEF-1 can implement the CAPIF-4 and CAPIF-5 reference points to the CAPIF core function. B.3 Integrated deployment of 3GPP network exposure systems with the CAPIF B.3.1 General According to 3GPP TS 23.682 [2], when the CAPIF is supported, the SCEF supports the API provider domain functions. According to 3GPP TS 23.501 [3], when the CAPIF is supported,the NEF supports the API provider domain functions. B.3.2 Deployment model B.3.2.1 General The SCEF and the NEF may be integrated with a single CAPIF core function to offer their respective service APIs to the API invokers. The following deployment model is possible for integrated deployment of the SCEF and the NEF with the CAPIF core function. B.3.2.2 Integrated deployment of the SCEF and the NEF with the CAPIF Figure B.3.2.2-1 illustrates integrated deployment of the SCEF and the NEF with the CAPIF. Figure B.3.2.2-1: Integrated deployment of the SCEF and the NEF with the CAPIF The CAPIF core function, the SCEF and the NEF are deployed in the PLMN trust domain, where the CAPIF core function takes the role of a unified gateway and provides services to different API invokers. The API invokers obtains the T8 and N33 service API information and the corresponding entry point details from the CAPIF core function via CAPIF-1 or CAPIF-1e reference points. The API invokers can interact independently with the SCEF, the NEF and the 3rd party API exposing functions via CAPIF-2 or CAPIF-2e reference points. In this case, T8 and N33 can be reused to implement the service specific aspects of CAPIF-2 or CAPIF-2e reference points for the corresponding service API interactions of the SCEF and the NEF respectively. The SCEF and the NEF applies any service API access policy control to the interactions between the API invokers and the T8 and N33 service APIs respectively by communicating with the same CAPIF core function via the CAPIF-3 reference point. Annex C (informative): CAPIF role in charging C.1 General This annex provides the information about the role of CAPIF in charging service API invocations. The common architecture for charging is illustrated in clause 4 of 3GPP TS 32.240 [6]. There are two charging mechanisms - offline charging and online charging. The role of CAPIF in both these charging mechanims is illustrated for informational purpose in this subclause. The API invocations are subjected to charging (online, offline) as illustrated in figure C.1-1. NOTE: As there are no impacts on CAPIF's role in charging due to deployment of 3rd party trust domain, it is not illustrated in the figures. Figure C.1-1: CAPIF role in charging C.2 CAPIF role in online charging The API invocations are subjected to online charging as illustrated in figure C.1-1. The API exposing function provides the API invocation charging information to the CAPIF core function. The CAPIF core function further interacts with an online charging system in real-time by providing the charging information and further the CAPIF core function receives the authorization corresponding to the charging information. NOTE: The online charging architecture for CAPIF including specification of online charging system entities and reference points is under the responsibility of SA5. C.3 CAPIF role in offline charging The API invocations are subjected to offline charging as illustrated in figure C.1-1. The API exposing function provides the API invocation charging information to the CAPIF core function. The CAPIF core function provides the charging information to the offline charging system. The offline charging system generates the CDRs for the API invocation and further transfers the CDR files to the billing domain. NOTE: The offline charging architecture for CAPIF including specification of offline charging system entities and reference points is under the responsibility of SA5. Annex D (informative): CAPIF relationship with external API frameworks This annex provides the relationship of CAPIF with the OMA Network APIs and the ETSI MEC API framework. The relationship of CAPIF with these external API frameworks is illustrated in the table D-1. "Yes" means that the external API framework supports the CAPIF functionality, "No" means that the API framework does not support the CAPIF functionality, and "Partial" means that it provides a mechanism that partially supports the CAPIF functionality. Table D-1: CAPIF relationship with external API frameworks CAPIF functionalities OMA Network APIs ETSI MEC API framework Supported Reference Supported Reference Publish and discover service API information Partial (see NOTE) OMA-TS-NGSI_Registration_and_Discovery [11] Yes ETSI GS MEC 011 [7] Topology hiding of the service Yes Individual API exposing function Yes Individual API exposing function API invoker authentication to access service APIs Partial OMA-ER_Autho4API [9] Partial ETSI GS MEC 009 [8] API invoker authorization to access service APIs Partial OMA-ER_Autho4API [9] Partial ETSI GS MEC 009 [8] Charging on invocation of service APIs No No Lifecycle management of service APIs No No Monitoring service API invocations No No Logging API invoker onboarding and service API invocations No No Auditing service API invocations No No Onboarding API invoker to CAPIF No No CAPIF authentication of API invokers No No Service API access control Partial OMA-ER_Autho4API [9] Partial ETSI GS MEC 009 [8] Secure API communication Yes OMA-ER_Autho4API [9] Yes ETSI GS MEC 009 [8] Policy configuration No No API protocol stack model Partial for REST: OMA-TS_REST_NetAPI_Common [10] Partial for REST: ETSI GS MEC 009 [8] API security protocol Partial OMA-ER_Autho4API [9] Partial ETSI GS MEC 009 [8] CAPIF support for service APIs from multiple providers No No NOTE: OMA-TS-NGSI_Registration_and_Discovery [11] is only applicable to a specific type of web services (OWSER using UDDI and WSDL). Annex E (normative): Configuration data for CAPIF The configuration data is stored in the CAPIF core function and provided by the CAPIF administrator. The configuration data for CAPIF is specified in table E-1. Table E-1: Configuration data for CAPIF Reference Parameter description Subclause 4.2.2 List of published service API discovery restrictions > Service API identification > API invoker identity information > Service API category Subclause 4.7.2 List of service API log storage durations > Service API identification > Service API log storage duration (in hours) (see NOTE) Subclause 4.7.4 List of API invoker interactions log storage durations > Service API identification API invoker interactions log storage duration (in hours) (see NOTE) Subclause 4.10 List of access control policy per API invoker and optionally per network slice > Volume limit on service API invocations (total number of invocations allowed) > Time limit on service API invocations (The time range of the day during which the service API invocations are allowed) > Rate limit on service API invocations (allowed service API invocations per second) > Service API identification > API invoker identity information > Network Slice Info Subclause 8.34.3 Group context information > Group identifier > List of UE IDs (group members) > UE identifier of the Group Resource Owner > Authorization information related to the list of supported applications >> Application identifier >> Purpose >> Scope NOTE: If no value is set for the duration, the duration is assumed to be unlimited. Annex F (informative): Examples of API invoker roles in CAPIF The figure F-1 provides examples of API invoker roles in CAPIF and illustrates the usage of CAPIF capabilities. BSS/OSS System: The BSS/OSS system of MNO enables the business relationship with the Application Service Providers (the consumers of the service APIs exposed by the MNO's exposure platform). The BSS/OSS system as an API invoker invoke the CAPIF APIs as per its business logic. Figure F-1: Examples of API invoker roles in CAPIF Editor's note: More description about the Examples of API invoker roles in CAPIF is FFS. Annex G (informative): API invoker with a frontend and backend component In clause 6.3.2 it is highlighted that the API invoker can be either an application on a server or an application on a UE. When considering the UE, the application can comprise of a frontend component on a UE plus a server-side backend component. The motivation for such an arrangement is to address security vulnerabilities associated with issuing access tokens to client-side entities (i.e., an API invoker as an application on a UE), e.g., persistent token theft. When the API invoker is deployed with a backend component in the network, the backend component is responsible for authentication and authorization procedures towards the CCF Authorization Function. The backend component can proxy service API discovery and invocation requests initiated by the API invoker frontend. This arrangement is depicted in Figure G-1. Figure G-1: High level functional RNAA architecture for CAPIF supporting an application with a frontend / backend component Editor's note: The security vulnerabilities associated with issuing access tokens to client-side entities will be addressed by SA3 and whether the split frontend / backend API invoker requires further specification, e.g., considerations for exchanging UE identity information when seeking resource owner authorization. Annex H (informative): AEF instantiation As illustrated in figure H-1, CAPIF architecture supports AEFs from multiple API providers (e.g. MNO, 3rd party). The instances of such AEFs are managed by the respective management systems of the API provider (e.g. PLMN management system, 3rd party management system). The AMF monitors the events reported by the CAPIF core function. These events can be utilized to trigger AEF instantiation by the PLMN management system or 3rd party management system. The AMF can utilize the services of PLMN or 3rd party management systems (e.g. trigger instantiation of corresponding AEFs) via the APIs exposed by the PLMN or 3rd party management systems. It is upto implementation of CAPIF to utilize the services of the PLMN and/or 3rd party management systems for AEF instantiation. Figure H-1: AEF instantiation Annex I (informative): Change history Change history Date Meeting TDoc CR Rev Cat Subject/Comment New version 2017-10 SA6#19 S6-171274 TS skeleton 0.0.0 2017-10 SA6#19 Implementation of the following p-CRs approved by SA6: S6-171444; S6-171343; S6-171445; S6-171446; S6-171466; S6-171448; S6-171348; S6-171449; S6-171359; S6-171467; S6-171451; S6-171452; S6-171362; S6-171463; S6-171356; S6-171355; S6-171453; S6-171454; S6-171455; S6-171464; S6-171468; S6-171350; S6-171349; S6-171407. 0.1.0 2017-12 SA6#20 Implementation of the following p-CRs approved by SA6: S6-171630; S6-171631; S6-171633; S6-171648; S6-171650; S6-171658; S6-171659; S6-171692; S6-171693; S6-171694; S6-171695; S6-171698; S6-171699; S6-171700; S6-171702; S6-171704; S6-171705; S6-171706; S6-171711; S6-171712; S6-171713; S6-171819; S6-171820; S6-171821; S6-171822; S6-171823; S6-171848; S6-171855; S6-171865; S6-171876. 0.2.0 2017-12 SA#78 SP-170901 Submitted to SA#78 for approval 1.0.0 2018-01 SA#78 SP-170901 MCC Editorial update for publication after TSG SA approval (SA#78) 15.0.0 2018-04 SA#79 SP-180156 0001 1 F Use of specific ETSI and OMA references 15.1.0 2018-04 SA#79 SP-180156 0002 F Corrections for CAPIF-1e and CAPIF-2e 15.1.0 2018-04 SA#79 SP-180156 0003 F Miscellaneous corrections to procedures and information flows 15.1.0 2018-04 SA#79 SP-180156 0004 1 F Addition of offboarding to functional entities and reference points description 15.1.0 2018-04 SA#79 SP-180156 0005 1 D Editorial corrections 15.1.0 2018-04 SA#79 SP-180156 0006 2 B Solution to EN on revoking authorization based on access control 15.1.0 2018-04 SA#79 SP-180156 0007 3 F Configuration items for CAPIF 15.1.0 2018-04 SA#79 SP-180156 0008 3 F Update to CAPIF relationship with 3GPP EPS and 5GS 15.1.0 2018-04 SA#79 SP-180156 0009 1 F Solution to EN on policy synchronization 15.1.0 2018-04 SA#79 SP-180156 0010 2 F CAPIF utilization by service APIs 15.1.0 2018-04 SA#79 SP-180156 0011 1 F Proposal for definition for PLMN trust domain 15.1.0 2018-06 SA#80 SP-180374 0013 1 F Correction for the details of service API information 15.2.0 2018-06 SA#80 SP-180374 0014 1 F Correction for usage of service API identification information 15.2.0 2018-06 SA#80 SP-180374 0019 2 D Editorial correction of TS 23.222 (CAPIF stage2) 15.2.0 2018-06 SA#80 SP-180375 0012 2 B Architecture functional model to support multiple API providers 16.0.0 2018-06 SA#80 SP-180375 0015 1 B Service API publish and discovery requirements for 3rd party API providers 16.0.0 2018-06 SA#80 SP-180375 0016 1 B Charging requirements for 3rd party API providers 16.0.0 2018-06 SA#80 SP-180375 0017 1 B OAM requirements for 3rd party API providers 16.0.0 2018-06 SA#80 SP-180375 0018 2 B CAPIF interconnection requirements 16.0.0 2018-06 SA#80 SP-180375 0020 2 F Updating representation of deployment models 16.0.0 2018-09 SA#81 SP-180675 0021 2 B Integrated CAPIF with 3GPP EPS and 5GS network exposure 16.1.0 2018-09 SA#81 SP-180675 0022 1 C Enhancement to the functional model deployments 16.1.0 2018-09 SA#81 SP-180675 0023 2 B Enhancement to reference points for eCAPIF 16.1.0 2018-09 SA#81 SP-180674 0029 1 A Update API naming convention 16.1.0 2018-09 SA#81 SP-180674 0030 2 A Alignment of APIs 16.1.0 2018-09 SA#81 SP-180674 0031 1 A Alignment to SA3 CAPIF TS 16.1.0 2018-09 SA#81 SP-180674 0032 1 Alignment to SA3 authentication procedure 16.1.0 2018-09 SA#81 SP-180675 0033 3 B Functional architecture for CAPIF interconnection 16.1.0 2018-12 SA#82 SP-181176 0034 3 B Topology hiding enhancement 16.2.0 2018-12 SA#82 SP-181176 0035 2 B API publish and API discover for CAPIF interconnection 16.2.0 2018-12 SA#82 SP-181176 0036 1 C Architectural requirements for identities 16.2.0 2018-12 SA#82 SP-181176 0038 2 B Architectural requirements for provider domain entities interaction 16.2.0 2018-12 SA#82 SP-181176 0039 2 B Update API invoker API list 16.2.0 2018-12 SA#82 SP-181175 0043 2 A API invoker's onboarding response rel16 16.2.0 2019-03 SA#83 SP-190072 0044 2 F Update procedures with topology hidding 16.3.0 2019-03 SA#83 SP-190072 0045 2 B API sharing for CCF interconnection 16.3.0 2019-03 SA#83 SP-190072 0046 2 B API invocation request routing with topology hiding 16.3.0 2019-03 SA#83 SP-190072 0048 1 C Interactions between API exposing functions 16.3.0 2019-03 SA#83 SP-190072 0049 1 B Service API discovery involving multiple CCFs 16.3.0 2019-03 SA#83 SP-190072 0050 2 B Multiple CCFs deployment in a PLMN trust domain 16.3.0 2019-03 SA#83 SP-190072 0051 2 B Service API discover for CAPIF interconnection 16.3.0 2019-03 SA#83 SP-190072 0052 1 B Architectural requirements for registration of API provider domain functions 16.3.0 2019-03 SA#83 SP-190072 0053 2 B Procedures for registration of API provider domain functions 16.3.0 2019-03 SA#83 SP-190072 0054 1 B Updates to AEF procedures for 3rd party trust domain 16.3.0 2019-03 SA#83 SP-190072 0055 1 B Updates to APF procedures for 3rd party trust domain 16.3.0 2019-03 SA#83 SP-190072 0056 1 B Updates to AMF procedures for 3rd party trust domain 16.3.0 2019-03 SA#83 SP-190072 0057 - B Updates to CAPIF events procedures for 3rd party trust domain 16.3.0 2019-06 SA#84 SP-190483 0058 1 F Clarification to routing rule of service API invocation 16.4.0 2019-06 SA#84 SP-190483 0059 3 F Functional model update with reference points 16.4.0 2019-06 SA#84 SP-190483 0060 2 B Update to service API publish for CAPIF interconnection 16.4.0 2019-06 SA#84 SP-190483 0061 2 B Serving area and domain of service API for CAPIF interconnection 16.4.0 2019-06 SA#84 SP-190483 0062 1 B 3rd party trust domain with network exposure and charging aspects of 3GPP systems 16.4.0 2019-06 SA#84 SP-190483 0063 1 B Interface based representation of CAPIF architecture 16.4.0 2019-09 SA#85 SP-190828 0064 1 F Clarification and alignment with publish request information flows 16.5.0 2019-12 SA#86 SP-191107 0065 F Correction on usage of service API information in access control message 16.6.0 2020-03 SA#87-E SP-200112 0066 1 F Shared CAPIF provider domain info in interconnection 16.7.0 2020-03 SA#87-E SP-200116 0067 2 B Serving area information for service APIs to support edge applications 17.0.0 2020-07 SA#88-E SP-200337 0069 A Add consumer for discover and publish service APIs 17.1.0 2020-07 SA#88-E SP-200337 0071 A Add obtaining routing info service API 17.1.0 2020-07 SA#88-E SP-200337 0073 1 A Correct API topology hiding 17.1.0 2020-07 SA#88-E SP-200337 0075 1 A Correction for CAPIF interconnection IEs 17.1.0 2020-09 SA#89-E SP-200840 0077 3 F Correction for API routing information 17.2.0 2020-12 SA#90-E SP-200997 0078 2 B Support AEF location and API invoker interface for edge application 17.3.0 2021-04 SA#91-E SP-210183 0079 4 F Clarification of Service-based interfaces interaction within CAPIF 17.4.0 2021-06 SA#92-E SP-210482 0082 A API provider management API 17.5.0 2022-06 SA#96 SP-220471 0084 1 A Corrections to API invoker onboarding/offboarding in TS 23.222 17.6.0 2022-09 SA#97 SP-220918 0089 A Corrections to API invoker onboarding/offboarding in TS 23.222 17.7.0 2022-12 SA#98-e SP-221250 0090 1 B Additional CAPIF architectural requirements for SNA 18.0.0 2022-12 SA#98-e SP-221250 0091 2 B CAPIF business relationship updates for SNA 18.0.0 2022-12 SA#98-e SP-221250 0092 2 B CAPIF functional model updates for SNA 18.0.0 2022-12 SA#98-e SP-221250 0093 2 B API invoker obtaining authorization from resource owner 18.0.0 2022-12 SA#98-e SP-221250 0094 1 B Discover a proper AEF with owner information 18.0.0 2022-12 SA#98-e SP-221250 0095 2 B Reducing resource owner consent inquiry in a nested API invocation 18.0.0 2022-12 SA#98-e SP-221239 0096 2 B CAPIF extensibility as requested by ETSI ISG MEC 18.0.0 2023-03 SA#99 SP-230295 0098 B Discover proper AEF in interconnection 18.1.0 2023-03 SA#99 SP-230296 0099 1 B Solve CAPIF extensibility EN 18.1.0 2023-03 SA#99 SP-230295 0100 1 B API invoker clarification 18.1.0 2023-03 SA#99 SP-230295 0101 1 D Modify a terminology for SNA 18.1.0 2023-03 SA#99 SP-230286 0102 2 B New IE(Service KPI) in Service API publish request 18.1.0 2023-03 SA#99 SP-230295 0103 2 B Discover proper AEF with IP information 18.1.0 2023-03 SA#99 SP-230292 0104 B Support onboarding expiration 18.1.0 2023-03 SA#99 SP-230296 0105 2 F Resolving editor’s notes about TS reference 18.1.0 2023-03 SA#99 SP-230295 0106 2 B Adding descriptions of new functional entities and reference points 18.1.0 2023-06 SA#100 SP-230714 0109 2 B Support CAPIF in SNPN 18.2.0 2023-06 SA#100 SP-230712 0111 4 B Service API status monitoring 18.2.0 2023-06 SA#100 SP-230713 0112 B Clarification that RNAA is for both 4G and 5G 18.2.0 2023-06 SA#100 SP-230713 0113 2 B SNAAPP alignment with SA3 18.2.0 2023-06 SA#100 SP-230713 0114 2 B Overview of CAPIF operations for RNAA scenarios 18.2.0 2023-06 SA#100 SP-230714 0115 3 B CAPIF add service procedure for update of subscriptions 18.2.0 2023-06 SA#100 SP-230714 0116 5 B Alignment among CAPIF provider (trust) domains 18.2.0 2023-12 SA#102 SP-231547 0122 2 A Editorial corrections 18.3.0 2023-12 SA#102 SP-231569 0125 1 F Solve EN related to SA3 18.3.0 2023-12 SA#102 SP-231569 0126 2 F Add response to RNAA procedural flows and correct cross-references 18.3.0 2023-12 SA#102 SP-231569 0128 2 F Clarify how to monitor service API status when the APF is unable to update service API status 18.3.0 2023-12 SA#102 SP-231569 0129 2 F Add CAPIF words to Abbreviations 18.3.0 2023-12 SA#102 SP-231569 0133 6 F CAPIF Architecture alignment with SA3 RNAA aspects 18.3.0 2023-12 SA#102 SP-231546 0136 A API Description Correction 18.3.0 2023-12 SA#102 SP-231569 0137 1 F API invoker authorization corrections 18.3.0 2023-12 SA#102 SP-231545 0141 A Security API corrections 18.3.0 2023-12 SA#102 SP-231569 0147 2 F Editorial corrections regarding RNAA 18.3.0 2023-12 SA#102 SP-231569 0149 2 F Corrections for CAPIF revocation of API Invoker's authorization based on RNAA 18.3.0 2023-12 SA#102 SP-231569 0150 1 F Corrections for CAPIF deployment models supporting RNAA 18.3.0 2023-12 SA#102 SP-231570 0131 2 B Slice-based service API exposure 19.0.0 2023-12 SA#102 SP-231570 0144 1 F Service API unpublish for CAPIF interconnection 19.0.0 2023-12 SA#102 SP-231570 0145 1 F Service API retrieval for CAPIF interconnection 19.0.0 2023-12 SA#102 SP-231570 0146 3 F Service API update for CAPIF interconnection 19.0.0 2024-03 SA#103 SP-240317 0151 1 D Align cross-references to the appropriate subclauses of TS 33.122 19.1.0 2024-03 SA#103 SP-240317 0152 1 F Responsibilities of CAPIF API provider domain functions 19.1.0 2024-03 SA#103 SP-240310 0154 2 A Consistent use of term "resource owner" 19.1.0 2024-03 SA#103 SP-240317 0157 2 D Editorial correction for topology hiding 19.1.0 2024-03 SA#103 SP-240317 0158 1 F Correction cardinality IE service API unpublish for CAPIF interconnection 19.1.0 2024-06 SA#104 SP-240755 0162 1 A Corrections to Deregister_API_Provider operation 19.2.0 2024-06 SA#104 SP-240755 0167 2 A Correction for Discover service APIs 19.2.0 2024-06 SA#104 SP-240764 0169 1 A Add missing function to resource owner function 19.2.0 2024-06 SA#104 SP-240756 0174 3 A Alignment of "API type" with "API category" terminology 19.2.0 2024-06 SA#104 SP-240755 0180 2 A Correction for Service API discovery involving multiple CCFs 19.2.0 2024-06 SA#104 SP-240764 0181 1 A Reducing authorization information inquiry in a nested API invocation 19.2.0 2024-06 SA#104 SP-240764 0185 3 A Correction to clause 6.2.3 19.2.0 2024-09 SA#105 SP-241213 0188 2 A Correction to clause 8.3.2.1 19.3.0 2024-09 SA#105 SP-241213 0190 2 A Correction to Interconnection API publish 19.3.0 2024-09 SA#105 SP-241213 0192 2 A Correction to Interconnection service API discover 19.3.0 2024-09 SA#105 SP-241217 0194 2 A Rel-19 Add to Definitions and Abbreviations 19.3.0 2024-09 SA#105 SP-241217 0196 1 A Rel-19 Correction on Resource owner 19.3.0 2024-09 SA#105 SP-241228 0197 3 F Update the CAPIF business relationships 19.3.0 2024-12 SA#106 SP-241714 0198 1 F Rel-19 Correction on Getting Service APIs for CAPIF Interconnection 19.4.0 2024-12 SA#106 SP-241712 0200 3 A Correction for service API information 19.4.0 2024-12 SA#106 SP-241714 0201 1 B CAPIF interconnection 19.4.0 2024-12 SA#106 SP-241714 0202 1 B Update to API invoker Roles in CAPIF 19.4.0 2024-12 SA#106 SP-241714 0203 1 C Update business relationship for Rel-19 19.4.0 2024-12 SA#106 SP-241714 0205 4 B Requesting of collective resource owner authorization 19.4.0 2024-12 SA#106 SP-241714 0206 2 B Finer granularity of access control for service API 19.4.0 2024-12 SA#106 SP-241730 0207 1 F API discovery update and clarification 19.4.0 2024-12 SA#106 SP-241731 0208 2 F Align CAPIF API publish and discover with SA3 SNAAPP enhancement 19.4.0 2024-12 SA#106 SP-241714 0209 2 F Correction of the service API category 19.4.0 2024-12 SA#106 SP-241712 0211 2 A Resolving ENs without action 19.4.0 2024-12 SA#106 SP-241712 0213 2 A Resolving ENs adding SA3 references 19.4.0 2024-12 SA#106 SP-241714 0214 2 B API invoker onboarding 19.4.0 2024-12 SA#106 SP-241712 0216 2 A Adding invocation latency 19.4.0 2024-12 SA#106 SP-241712 0218 1 A API invoker obtaining authorization from resource owner 19.4.0 2024-12 SA#106 SP-241712 0220 1 A Terminology alignment: authorization vs consent 19.4.0 2024-12 SA#106 SP-241714 0221 2 B API invoker split into frontend and backend components 19.4.0 2024-12 SA#106 SP-241712 0225 1 A R19_Correction of Update API invoker’s API list 19.4.0 2024-12 SA#106 SP-241714 0226 2 B Enhancement to API invoker Authorization with the Purpose of Data Processing 19.4.0 2024-12 SA#106 SP-241714 0227 2 B Enhancement to API invoker Authorization with the Purpose of Data Processing 19.4.0 2024-12 SA#106 SP-241714 0228 2 B Exposure of User Sensitive Information 19.4.0 2024-12 SA#106 SP-241714 0230 4 B UE-deployed API invoker accessing other UEs’ resources of a group 19.4.0 2024-12 SA#106 SP-241714 0231 2 B Additional CAPIF Interconnection-related requirements 19.4.0 2024-12 SA#106 SP-241714 0232 2 B Additional RNAA-related requirements 19.4.0 2024-12 SA#106 SP-241714 0233 2 B Resource owner consent upon service API invocation 19.4.0 2024-12 SA#106 SP-241712 0235 2 A Clarify user consent storage 19.4.0 2025-03 SA#107 SP-250208 0236 1 B Updates to RNAA deployments 19.5.0 2025-03 SA#107 SP-250208 0241 1 C Addition of response elements in the CAPIF procedure in TS23.222 19.5.0 2025-03 SA#107 SP-250208 0243 2 B Procedure for Revoking Resource Owner Authorization 19.5.0 2025-03 SA#107 SP-250208 0244 3 B Procedure for CCF Obtaining Resource Owner Authorization 19.5.0 2025-03 SA#107 SP-250208 0248 1 B Solving ENs on CAPIF interconnection 19.5.0 2025-03 SA#107 SP-250208 0249 3 F UE accessing resources not owned by that UE 19.5.0 2025-03 SA#107 SP-250208 0251 1 F Correction to Procedure for API invoker obtaining authorization from resource owner 19.5.0 2025-03 SA#107 SP-250208 0252 3 F Corrections to UE-access of other UEs’ resources of a group 19.5.0 2025-03 SA#107 SP-250209 0253 1 F Service API category as discovery policy information 19.5.0 2025-03 SA#107 SP-250208 0254 B Solving ENs on finer granularity of access control for service API 19.5.0 2025-03 SA#107 SP-250208 0255 2 B Correction on Revocation on CAPIF interconnection 19.5.0 2025-03 SA#107 SP-250207 0256 2 F Clarification of the ROF and Authorization Function responsibilities 19.5.0 2025-03 SA#107 SP-250208 0257 3 B Clarification on resource owner consent upon service API invocation 19.5.0 2025-03 SA#107 SP-250208 0259 2 B Discover service APIs without onboarding 19.5.0 2025-03 SA#107 SP-250207 0260 2 F Clarification of the ROF and Authorization Function responsibilities 19.5.0 2025-03 SA#107 SP-250208 0261 2 B Proposal for AEF instantiation support in CAPIF 19.5.0 2025-03 SA#107 SP-250208 0264 1 F On mapping of active-inactive API states to SA5 solutions and aligning Service API Information descriptions 19.5.0 2025-03 SA#107 SP-250208 0265 2 B Group Information Provisioning in CAPIF to support RNAA 19.5.0
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1 Scope
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This document defines the stage-2 service description for the IP Multimedia Core Network Subsystem (IMS), which includes the elements necessary to support IP Multimedia (IM) services. ITU‑T Recommendation I.130 [4] describes a three-stage method for characterisation of telecommunication services and ITU‑T Recommendation Q.65 [3] defines stage 2 of the method.
This document does not cover the Access Network functionality except as they relate to provision of IM services, these aspects are covered in the normative Annexes.
This document identifies the mechanisms to enable support for IP multimedia applications. In order to align IP multimedia applications wherever possible with non-3GPP IP applications, the general approach is to adopt non-3GPP specific IP based solutions.
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2 References
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The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or non‑specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
[1] 3GPP TS 23.002: "Network Architecture".
[2] CCITT Recommendation E.164: "Numbering plan for the ISDN era".
[3] CCITT Recommendation Q.65: "Methodology – Stage 2 of the method for the characterisation of services supported by an ISDN".
[4] ITU Recommendation I.130: "Method for the characterization of telecommunication services supported by an ISDN and network capabilities of an ISDN".
[5] 3GPP TS 33.310: "Network Domain Security (NDS); Authentication Framework (AF)".
[6] Void.
[7] 3GPP TS 23.221: "Architectural Requirements".
[8] 3GPP TS 22.228: "Service requirements for the IP multimedia core network subsystem".
[9] 3GPP TS 23.207: "End-to-end QoS concept and architecture".
[10] Void.
[10a] 3GPP TS 24.229: "IP Multimedia Call Control based on SIP and SDP; Stage 3".
[11] 3GPP TS 29.214: "Policy and Charging Control over Rx reference point".
[11a] 3GPP TS 29.207: "Policy control over Go interface".
[12] IETF RFC 3261: "SIP: Session Initiation Protocol".
[13] IETF RFC 3986: "Uniform Resource Identifiers (URI): Generic Syntax".
[14] IETF RFC 4282: "The Network Access Identifier".
[15] IETF RFC 3966: "The tel URI for Telephone Numbers".
[16] IETF RFC 3761 (April 2004): "The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)".
[16a] IETF RFC 4941: "Privacy Extensions for Stateless Address Autoconfiguration in IPv6".
[17] ITU Recommendation G.711: "Pulse code modulation (PCM) of voice frequencies".
[18] ITU Recommendation H.248: "Gateway control protocol".
[19] 3GPP TS 33.203: "Access Security for IP-based services".
[20] 3GPP TS 33.210: "Network Domain Security: IP network layer security".
[21] Void.
[22] 3GPP TR 22.941: "IP Based Multimedia Services Framework".
[23] 3GPP TS 23.060: "General Packet Radio Service (GPRS); Service description; Stage 2".
[24] 3GPP TS 23.003: "Technical Specification Group Core Network; Numbering, addressing and identification".
[25] 3GPP TS 32.240: "Telecommunication management; Charging management; Charging architecture and principles".
[26] 3GPP TS 32.260: "Telecommunication Management; Charging Management; IP Multimedia Subsystem (IMS) charging".
[27] 3GPP TS 22.071: "Technical Specification Group Services and System Aspects, Location Services (LCS); Service description, Stage 1".
[28] 3GPP TS 23.271: "Technical Specification Group Services and System Aspects, Functional stage 2 description of LCS".
[29] 3GPP TS 23.078: "Customised Applications for Mobile network Enhanced Logic (CAMEL) Phase 3 - Stage 2".
[29a] 3GPP TS 22.340: "IMS Messaging; Stage 1".
[30] 3GPP TS 29.228: "IP Multimedia (IM) Subsystem Cx and Dx Interfaces; Signalling flows and message contents".
[31] 3GPP TS 23.240: "3GPP Generic User Profile - Architecture; Stage 2".
[32] 3GPP TS 22.250: "IP Multimedia Subsystem (IMS) group management"; Stage 1".
[33] IETF RFC 2766: "Network Address Translation-Protocol Translation (NAT-PT)".
[34] IETF RFC 2663: "IP Network Address Translator (NAT) Terminology and Considerations".
[35] Void.
[36] 3GPP TS 23.141: "3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Presence Service".
[37] Void.
[38] IETF RFC 3840: "Indicating User Agent Capabilities in the Session Initiation Protocol (SIP)".
[39] IETF RFC 3323: "A Privacy Mechanism for the Session Initiation Protocol (SIP)".
[40] IETF RFC 3325: "Private Extensions to the Session Initiation Protocol (SIP) for Asserted Identity within Trusted Network".
[41] IETF RFC 3312: "Integration of resource management and Session Initiation Protocol (SIP)".
[42] IETF RFC 3841: "Caller Preferences for the Session Initiation Protocol (SIP)".
[43] IETF RFC 3428: "Session Initiation Protocol (SIP) Extension for Instant Messaging".
[44] IETF RFC 3263: "Session Initiation Protocol (SIP): Locating SIP Servers".
[45] IETF RFC 5245: "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols".
[46] IETF RFC 5766: "Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN)".
[47] IETF RFC 5389: "Session Traversal Utilities for NAT (STUN)".
[48] IETF RFC 5626: "Managing Client Initiated Connections in the Session Initiation Protocol (SIP)".
[49] IETF RFC 5627: "Obtaining and Using Globally Routable User Agent URIs (GRUUs) in the Session Initiation Protocol (SIP)".
[50] IETF RFC 5628: "Registration Event Package Extension for Session Initiation Protocol (SIP) Globally Routable User Agent URIs (GRUUs)".
[51] IETF RFC 4787: "Network Address Translation (NAT) Behavioural Requirements for Unicast UDP".
[52] 3GPP TS 23.279: "Combining Circuit Switched (CS) and IP Multimedia Subsystem (IMS) services; Stage 2".
[53] 3GPP TS 22.173: "IMS Multimedia Telephony Service and supplementary services; Stage 1".
[54] 3GPP TS 23.203: "Policy and Charging Control architecture".
[55] 3GPP TS 23.107: "Quality of Service (QoS) concept and architecture".
[56] 3GPP TS 23.204: "Support of Short Message Service (SMS) over generic 3GPP Internet Protocol (IP) access".
[57] IETF RFC 4769: "IANA Registration for an Enumservice Containing Public Switched Telephone Network (PSTN) Signaling Information".
[58] 3GPP TS 23.167: "IP Multimedia Subsystem (IMS) emergency sessions".
[59] 3GPP TS 29.333: "Multimedia Resource Function Controller (MRFC) - Multimedia Resource Function Processor (MRFP) Mp Interface; Stage 3".
[60] 3GPP2 X.S0011: "cdma2000 Wireless IP Network Standard".
[61] 3GPP2 C.S0001-D: "Introduction to cdma2000 Spread Spectrum Systems - Revision D".
[62] 3GPP2 C.S0024-A: "cdma2000 High Rate Packet Data Air Interface Standard, April 2004".
[63] 3GPP2 C.S0084-000: "Overview for Ultra Mobile Broadband (UMB) Air Interface Specification".
[64] 3GPP TS 24.167: "3GPP IMS Management Object (MO); Stage 3".
[65] IETF RFC 3022: "Traditional IP Network Address Translator (Traditional NAT)".
[66] 3GPP TS 23.292: "IP Multimedia Subsystem (IMS) Centralized Services".
[67] 3GPP TS 23.237: "IP Multimedia Subsystem (IMS) Service Continuity".
[68] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[69] 3GPP TS 31.103: "Characteristics of the IP Multimedia Services Identity Module (ISIM) application".
[70] 3GPP TS 23.401: "General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access".
[71] 3GPP TS 23.218: "IP Multimedia (IM) session handling; IM call model; Stage 2".
[72] IETF RFC 3264: "An Offer/Answer Model with Session Description Protocol".
[73] 3GPP TS 23.333: "Multimedia Resource Function Controller (MRFC) - Multimedia Resource Function Processor (MRFP) Mp interface: Procedures Descriptions".
[74] 3GPP TS 23.334: " IMS Application Level Gateway (IMS-ALG) - IMS Access Gateway (IMS-AGW) interface: Procedures Descriptions".
[75] 3GPP TS 29.162: "Interworking between the IM CN subsystem and IP networks".
[76] 3GPP TS 26.114: "IP Multimedia Subsystem (IMS); Multimedia Telephony; Media handling and interaction".
[77] 3GPP TS 22.153: "Multimedia priority service".
[78] ETSI ES 282 003: "Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN); Resource and Admission Control Sub-System (RACS): Functional Architecture".
[79] 3GPP TS 29.328: "IP Multimedia (IM) Subsystem Sh Interface; Signalling flows and message contents".
[80] 3GPP TS 23.380: "IP Multimedia Subsystem (IMS); IMS Restoration Procedures".
[81] 3GPP TS 24.525: "Business trunking; Architecture and functional description".
[82] 3GPP TS 23.402: "Architecture Enhancements for non-3GPP accesses".
[83] 3GPP TS 33.328: "IP Multimedia (IM) Subsystem media plane security".
[84] IETF RFC 8825: "Overview: Real Time Protocols for Brower-based Applications".
[85] W3C: "WebRTC 1.0: Real-time Communication Between Browsers", W3C Recommendation, 26 January 2021, https://www.w3.org/TR/2021/REC-webrtc-20210126/.
[86] W3C: "Cross-Origin Resource Sharing", W3C Proposed Recommendation, 05 December 2013, http://www.w3.org/TR/2013/PR-cors-20131205/.
[87] ITU-T Recommendation T.140: "Protocol for multimedia application text conversation".
[88] IETF RFC 6455: "The WebSocket Protocol".
[89] IETF RFC 7118: "The WebSocket Protocol as a Transport for the Session Initiation Protocol (SIP)".
[90] IETF RFC 4571: "Framing Real-time Transport Protocol (RTP) and RTP Control Protocol (RTCP) Packets over Connection-Oriented Transport".
[91] 3GPP TS 24.610: "Communication HOLD (HOLD) using IP Multimedia (IM) Core Network (CN) subsystem".
[92] 3GPP TS 23.179: "Functional architecture and information flows to support mission critical communication services; Stage 2".
[93] 3GPP TS 23.501: "System Architecture for the 5G System; Stage 2".
[94] 3GPP TS 23.502: "Procedures for the 5G System; Stage 2".
[95] 3GPP TS 23.503: "Policy and Charging Control Framework for the 5G System; Stage 2".
[96] 3GPP TS 29.514: "5G System; Policy Authorization Service; Stage 3".
[97] 3GPP TS 23.632: "User data interworking, coexistence and migration; Stage 2".
[98] 3GPP TS 29.563: "5G System (5GS); Home Subscriber Server (HSS) services for interworking with Unified Data Management (UDM); Stage 3".
[99] 3GPP TS 36.300: "Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description".
[100] 3GPP TS 36.321: "Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification".
[101] 3GPP TS 38.300: "NR; NR and NG-RAN Overall Description".
[102] 3GPP TS 38.321: "NR; Medium Access Control (MAC) protocol specification".
[103] 3GPP TS 23.288: "Architecture enhancements for 5G System (5GS) to support network data analytics services".
[104] 3GPP TS 26.264: "IMS-based AR Real-Time Communication".
[105] 3GPP TS 24.186: "IMS Data Channel applications; Protocol specification".
[106] IETF RTC 4028: "Session Timers in the Session Initiation Protocol (SIP)".
[107] IETF draft-ietf-sipcore-callinfo-rcd-12: "SIP Call-Info Parameters for Rich Call Data".
Editor's note: The above document cannot be formally referenced until it is published as an RFC.
[108] IETF draft-ietf-stir-passport-rcd-26: "PASSporT Extension for Rich Call Data".
Editor's note: The above document cannot be formally referenced until it is published as an RFC.
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3 Definitions, symbols and abbreviations
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3.1 Definitions
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Refer to TS 23.002 [1] for the definitions of some terms used in this document.
For the purposes of the present document the terms and definitions given in TR 21.905 [68] and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [68].
For the purposes of the present document, the following terms and definitions given in TS 23.003 [24] apply:
- Distinct Public Service Identity
- Public User Identity
- Wildcarded Public User Identity
- Wildcarded Service User Identity
Alias Public User Identities: A set of Public User Identities that belong to the same alias group as specified in TS 29.228 [30].
ALG: Application Level Gateway (ALG) is an application specific functional entity that allows communication between disparate address realm or IP versions, e.g. an IPv6 node to communicate with an IPv4 node and vice versa, when certain applications carry network addresses in the payloads like SIP/SDP. NA(P)T-PT or NA(P)T is application unaware whereas ALGs are application specific translation entities that allow a host running an application to communicate transparently with another host running the same application but in a different IP version or IP address realm. See IETF RFC 2663 [34] for more details.
For IMS, an IMS ALG provides the necessary application function for SIP/SDP protocols in order to communicate between different address realms or IP versions, e.g. IPv6 and IPv4 SIP applications.
Application data channel: A data channel within an IMS session used to transfer data of data channel applications between UEs or between the UE and the network.
AR Application Server: An application server used to control the service logic related to AR communication via IMS data channel.
Bootstrap data channel: A data channel established within an IMS session between the UE and the network, to transfer a graphical user interface that can include a list of data channel applications.
Business trunking: as defined in TS 24.525 [81].
Data channel application: A HTML page including JavaScript(s) and optionally image(s) and style sheet(s). It is downloaded from the network to the UE through the bootstrap data channel.
DC Application Server: An application server that interacts with the DCSF and the DC media function for data channel traffic handling.
Distinct Public User Identity: used in relation to wildcarded Public User/Service Identities to denote an explicitly provisioned Public User/Service Identity. See more details in TS 23.003 [24].
Entry point: In the case that border control concepts are to be applied in an IM CN subsystem, then these are to be provided by capabilities within the IBCF and the IBCF acts as an entry point for this network (instead of the I‑CSCF). In this case the IBCF and the I‑CSCF can be co-located as a single physical node. If border control concepts are not applied, then the I-CSCF is considered as an entry point of a network. If the P‑CSCF is in the home network, then the I‑CSCF is considered as an entry point for this document.
Exit point: If operator preference requires the application of border control concepts then these are to be provided by capabilities within the IBCF and requests sent towards another network are routed via a local network exit point (IBCF), which will then forward the request to the other network (discovering the entry point if necessary).
Geographical Identifier: A Geographical Identifier identifies a geographical area within a country or territory. See more details in clause E.8.
Geo-local service number: A local service number that is used to access a service in the roamed network (a local service where the subscriber is located).
Home local service number: A local service number is used to access a service that is located in the home network of the user.
HSS Group ID: This refers to one or more SBI capable HSS instances managing a specific set of IMPIs/IMPUs.
IMC: IMS Credentials as defined in TR 21.905 [68].
IMS application reference: An IMS application reference is the means by which an IMS communication service identifies an IMS application.
IMS application: An IMS application is an application that uses an IMS communication service(s) in order to provide a specific service to the end-user. An IMS application utilises the IMS communication service(s) as they are specified without extending the definition of the IMS communication service(s).
IMS communication service identifier: An IMS communication service identifier uniquely identifies the IMS communication service associated with the particular IMS request.
IMS communication service: An IMS communication service is a type of communication defined by a service definition that specifies the rules and procedures and allowed medias for a specific type of communication and that utilises the IMS enablers.
IMS enabler: An IMS enabler is a set of IMS procedures that fulfils specific function. An IMS enabler may be used in conjunction with other IMS enablers in order to provide an IMS communication service.
Instance identifier: An identifier, that uniquely identifies a specific UE amongst all other UEs registered with the same Public User Identity.
Inter-IMS Network to Network Interface: The interface which is used to interconnect two IM CN subsystem networks. This interface is not constrained to a single protocol.
IP Flow: Unidirectional flow of IP packets with the following properties:
- same destination IP address and port number;
- same source IP address and port number;
- same transport protocol (port numbers are only applicable if used by the transport protocol).
IP-Connectivity Access Network: refers to the collection of network entities and interfaces that provides the underlying IP transport connectivity between the UE and the IMS entities. An example of an "IP-Connectivity Access Network" is GPRS.
IP SM GW (IP short message gateway): An IP SM GW is an AS providing the support of Short Message Service of the IMS domain. See more details in TS 23.204 [56].
Local Service Number: A local service number is a telephone number in non-international format. A local service number is used to access a service that may be located in the home network of the user (home local service number) or the roamed network of the user (geo-local service number).
Media Flow: One or more IP flows carrying a single media instance, e.g. an audio stream or a video stream. In the context of this specification the term Media Flow is used instead of IP Flow regardless of whether the actual IP packet corresponds to media plane information (e.g. audio RTP flow) or control signalling (e.g. RTCP or SIP Signalling).
MPS: Based on TS 22.153 [77]. Multimedia Priority Service allows authorized users to obtain and maintain radio and network resources with priority, also during national security or emergency situations when PLMN congestion may occur.
MPS session: A session (e.g. voice, video, data session) for which priority treatment is applied for allocating and maintaining radio and network resources.
MPS for Messaging: Within the scope of this specification, IMS Immediate Messaging and IMS Session-based Messaging delivered with MPS priority.
MPS-subscribed UE: A UE having a USIM with MPS indication set and having an MPS subscription in the HPLMN.
NAT-PT/NAPT-PT: NAT-PT uses a pool of globally unique IPv4 addresses for assignment to IPv6 nodes on a dynamic basis as sessions are initiated across the IP version boundaries. NAT-PT binds addresses in IPv6 network with addresses in IPv4 network and vice versa to provide transparent routing between the two IP domains without requiring any changes to end points, like the UE. NAT-PT needs to track the sessions it supports and mandates that inbound and outbound data for a specific session traverse the same NAT-PT router.
NAPT-PT provides additional translation of transport identifier (e.g. TCP and UDP port numbers, ICMP query identifiers). This allows the transport identifiers of a number of IPv6 hosts to be multiplexed into the transport identifiers of a single assigned IPv4 address. See IETF RFC 2766 [33] for more details.
Network Address Translation (NA(P)T): method by which IP addresses are mapped from one group to another, transparently to end users. Network Address Port Translation, or NA(P)T is a method by which many network addresses and their TCP/UDP (Transmission Control Protocol/User Datagram Protocol) ports are translated into a single network address and its TCP/UDP ports. See RFC 3022 [65] for further details.
Outbound: Managing Client Initiated Connections in the Session Initiation Protocol (Outbound) defines behaviours for User Agents, registrars and proxy servers that allow requests to be delivered on existing connections established by the User Agent. See RFC 5626 [48] for further details.
Preferred Circuit Carrier Access: An IMS service that allows a specific long distance circuit carrier to be selected for a long distance call.
Preferred Circuit Carrier Selection: An IMS service that allows the subscriber to select a long distance circuit carrier per call when dialling a call origination.
Rich Call Data (RCD) server: It refers to a server in a third party network storing IMS subscriber specific RCD information.
Rich Call Data (RCD) server address: It refers to the address of an RCD server.
Rich Call Data (RCD) information: It refers to a collection of properties associated with an IMS subscriber. Such properties can be caller name, Email address, telephone number, job title and characteristics of an organization. Details of the properties in the context of RCD can be found in draft-ietf-sipcore-callinfo-rcd-12 [107].
Rich Call Data (RCD) URL: It refers to the URL from where RCD information of a specific IMS subscriber stored at an RCD server can be retrieved from.
Rich Call Data (RCD) properties: It refers to the RCD related parameters (e.g. RCD server address, RCD URL, RCD information) stored in HSS.
Service User: According to TS 22.153 [77].
Stand-alone Non-Public Network: A non-public network not relying on network functions provided by a PLMN.
STUN: Simple Traversal of UDP Through NAT (STUN), provides a toolkit of functions. These functions allow entities behind a NAT to learn the address bindings allocated by the NAT, to keep those bindings open and communicate with other STUN-aware devices to validate connectivity. See RFC 5389 [47] for further details.
STUN Keep-alive: Is a usage of STUN, to keep NAT bindings open.
STUN Relay: Is a usage of STUN, that allows a client to request an address on the STUN server itself, so that the STUN server acts as a relay. See IETF RFC 5766 [46] for further details.
Subscriber: A Subscriber is an entity (comprising one or more users) that is engaged in a Subscription with a service provider. The subscriber is allowed to subscribe and unsubscribe services, to register a user or a list of users authorized to enjoy these services and also to set the limits relative to the use that users make of these services.
Transport address: A unique identifier of transport-layer address, i.e. a combination of a network address, protocol identifier and port number. For example, an IP address and a UDP port.
Standalone IMS Data Channel Session: An IMS session with only data channel media component(s) defined in TS 26.114 [76] without accompanying audio/video/messaging media.
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3.2 Symbols
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For the purposes of the present document the following symbols apply:
Cr Reference Point between an AS and an MRFC for media control.
Cx Reference Point between a CSCF and an HSS.
Dx Reference Point between an I‑CSCF and an SLF.
Gi Reference point between GPRS and an external packet data network.
Gm Reference Point between a UE and a P‑CSCF or between an IP-PBX and a P‑CSCF.
ISC Reference Point between a CSCF and an Application Server and between a CSCF and an MRB.
Iu Interface between the RNS and the core network. It is also considered as a reference point.
Ix Reference Point between IBCF and TrGW.
Ici Reference Point between an IBCF and another IBCF belonging to a different IM CN subsystem network or between an IBCF and an IP-PBX.
Izi Reference Point between a TrGW and another TrGW belonging to a different IM CN subsystem network.
Le Reference Point between an AS and a GMLC.
Ma Reference Point between an AS and an I‑CSCF.
Mb Reference Point used for IMS media transport to IP network services.
Mf Reference Point between a transit function and AS.
Mg Reference Point between an MGCF and a CSCF.
Mi Reference Point between a CSCF and a BGCF.
Mj Reference Point between a BGCF and an MGCF.
Mk Reference Point between a BGCF/IMS ALG and another BGCF.
Mm Reference Point between a IBCF/CSCF/BGCF/IMS ALG and an IP multimedia network.
Mr Reference Point between an CSCF and an MRFC.
Mr′ Reference Point between an AS and an MRFC for session control.
Mp Reference Point between MRFP and MRFC.
Ms Reference point between an IBCF and Application Server
Mw Reference Point between a CSCF and another CSCF.
Mx Reference Point between a CSCF/BGCF and IBCF.
Rc Reference Point between an AS and an MRB.
Sh Reference Point between an AS (SIP‑AS or OSA‑CSCF) and an HSS.
Si Reference Point between an IM-SSF and an HSS.
Ut Reference Point between UE and an Application Server.
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For the purposes of the present document, the abbreviations given in TR 21.905 [68] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905 [68].
5GS 5G System
API Application Program Interface
APN Access Point Name
AS Application Server
A2P Application to Person
BCSM Basic Call State Model
BG Border Gateway
BGCF Breakout Gateway Control Function
BS Bearer Service
CAMEL Customised Application Mobile Enhanced Logic
CAP Camel Application Part
CDR Charging Data Record
CN Core Network
CS Circuit Switched
CSCF Call Session Control Function
CSE CAMEL Service Environment
DC Data Channel
DCAR Data Channel Application Repository
DCMTSI Data Channel Multimedia Telephony Service for IMS
DCSF Data Channel Signalling Function
DHCP Dynamic Host Configuration Protocol
DNN Data Network Name
DNS Domain Name System
ECN Explicit Congestion Notification
ENUM E.164 Number Mapping
GGSN Gateway GPRS Support Node
GLMS Group and List Management Server
GMLC Gateway Mobile Location Centre
GRUU Globally Routable User Agent URI
GUP Generic User Profile
HSS Home Subscriber Server
IBCF Interconnection Border Control Function
I‑CSCF Interrogating‑CSCF
IETF Internet Engineering Task Force
IM IP Multimedia
IMC IMS Credentials
IMS IP Multimedia Core Network Subsystem
IMS ALG IMS Application Level Gateway
IMSI International Mobile Subscriber Identifier
IN Intelligent Network
IP Internet Protocol
IPv4 Internet Protocol version 4
IPv6 Internet Protocol version 6
IP‑CAN IP-Connectivity Access Network
IP‑SM‑GW IP Short Message Gateway
ISDN Integrated Services Digital Network
ISIM IMS SIM
ISP Internet Service Provider
ISUP ISDN User Part
IWF Interworking Function
NP Number portability
MAP Mobile Application Part
MGCF Media Gateway Control Function
MGF Media Gateway Function
MRB Media Resource Broker
MRFC Multimedia Resource Function Controller
MRFP Multimedia Resource Function Processor
NAI Network Access Identifier
NAPT Network Address Port Translation
NAT Network Address Translation
NA(P)T-PT Network Address (Port-Multiplexing) Translation-Protocol Translation
II-NNI Inter-IMS Network to Network Interface
OSA Open Services Architecture
P2A Person to Application
P2P Person to Person
P‑CSCF Proxy‑CSCF
PCC Policy and Charging Control
PCEF Policy and Charging Enforcement Function
PCRF Policy and Charging Rules Function
PDN Packet Data Network
PDP Packet Data Protocol e.g. IP
P‑GRUU Public Globally Routable User Agent URI
PLMN Public Land Mobile Network
PSI Public Service Identity
PSTN Public Switched Telephone Network
QoS Quality of Service
RAB Radio Access Bearer
RCD Rich Call Data
RFC Request for Comments
SCS Service Capability Server
S‑CSCF Serving‑CSCF
SDP Session Description Protocol
SGSN Serving GPRS Support Node
SLF Subscription Locator Function
SNPN Stand-alone Non-Public Network
SSF Service Switching Function
SS7 Signalling System 7
SIM Subscriber Identity Module
SIP Session Initiation Protocol
S‑GW Signalling Gateway
TAS Telephony Application Server
T‑GRUU Temporary Globally Routable User Agent URI
THIG Topology Hiding Inter-network Gateway
TrGW Transition Gateway
UE User Equipment
UMTS Universal Mobile Telecommunications System
URL Universal Resource Locator
USIM UMTS SIM
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4 IP multimedia subsystem concepts
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4.0 General
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The IP Multimedia CN subsystem comprises all CN elements for provision of multimedia services. This includes the collection of signalling and media related network elements as defined in TS 23.002 [1]. IP multimedia services are based on an IETF defined session control capability which, along with multimedia transport capabilities, utilises the IP-Connectivity Access Network (this may include an equivalent set of services to the relevant subset of CS Services).
In order to achieve access independence and to maintain a smooth interoperation with wireline terminals across the Internet, the IP multimedia subsystem attempts to be conformant to IETF "Internet standards". Therefore, the interfaces specified conform as far as possible to IETF "Internet standards" for the cases where an IETF protocol has been selected, e.g. SIP and RTP.
The IP multimedia core network (IM CN) subsystem enables operators to offer their subscribers multimedia services. The IM CN subsystem should enable the convergence of and access to, voice, video, messaging, data and web-based technologies for the wireless and wireline user.
The complete solution for the support of IP multimedia applications consists of terminals, IP-Connectivity Access Networks (IP‑CAN) and the specific functional elements of the IM CN subsystem described in this technical specification. Examples of IP-Connectivity Access Network are:
- the GPRS core network with GERAN and/or UTRAN radio access networks; and
- EPC core network and E-UTRAN radio access network; and
- 5GS access network.
Figure 4.0 below represents the IMS reference architecture including interfaces towards CS network and other IP based multimedia Networks. Details of the roles of these nodes are described in clauses 4.6, 4.7 and 4.7a.
NOTE 1: Some entities defined as part of the IMS Subsystem can also be used by other subsystems.
NOTE 2: The Ici and Izi reference points are only applicable for IP Multimedia Networks that are IMS subsystems.
NOTE 3: In certain configuration, two entities can exchange SIP messages directly with each other without a reference point being defined between them (e.g. intermediate entity(ies) not record-routed).
Figure 4.0: Reference Architecture of the IP Multimedia Core Network Subsystem
A description of the functional entities can be found in TS 23.002 [1].
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4.1 Relationship to CS domain and the IP-Connectivity Access Network
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The IP multimedia subsystem utilizes the IP‑CAN to transport multimedia signalling and bearer traffic. IP‑CANs that maintain the service while the terminal moves, hide these moves from the IP multimedia subsystem.
The IP multimedia subsystem is independent of the CS domain although some network elements may be common with the CS domain. This means that it is not necessary to deploy a CS domain in order to support an IP multimedia subsystem based network.
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4.2 IMS services concepts
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4.2.1 Home-network based services
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4.2.1.1 Support of CAMEL or IN
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It shall be possible for an operator to offer access to services based on the CSE or IN Service Environment for its IM CN subsystem subscribers. It should be noted that there is no requirement for any operator to support CAMEL or IN services for their IM CN subsystem subscribers or for inbound roamers.
For more information refer to clause 4.2.4.
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4.2.1.2 Support of OSA
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It shall be possible for an operator to offer access to services based on OSA for its IM CN subsystem subscribers. This shall be supported by an OSA API between the Application Server (AS) and the network.
For more information refer to clause 4.2.4.
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4.2.1.3 Dynamic services interactions handling
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4.2.1.3.1 Service information exchanged between Application Servers
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To avoid conflicting interactions between services they execute, different ASs involved in the same IMS session (within an operator network or across networks) shall be able to exchange the following service interaction information:
- indication of services that have been performed and
- optionally, additional indication of services that should be further avoided.
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4.2.1.3.2 Handling by the Application Server
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If an AS provides one or more services, the AS may include service interaction information in SIP signalling, identifying the service that it has executed.
If an AS provides one or more services which are known to be negatively impacted by the subsequent execution of a service by another AS, the AS may include, in addition to the an indication of the services executed, service interaction information in SIP signalling, indicating the services that should be avoided.
An AS receiving a SIP message containing an indication
- that a service has been executed previously and/or
- that a service should be avoided,
may, depending on local policy, take this information into account. The service interaction information shall be such that an AS receiving this information should not be able to misinterpret the information and shall ignore such information that it does not recognize.
Service interaction information for standardized services shall be standardized but there shall also be the ability to exchange globally unique service information for non-standardized services.
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4.2.1.3.3 Deletion of services interaction information
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The service interaction information shall be removed when it is sent to the UE via P-CSCF or to an entity outside the trust domain or when it is not in compliance with service level agreements with other domains.
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4.2.2 Support of numbers in non-international format in the IMS
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Phone or telephone numbers which are not in the international format can allow the access of the visited services (local service numbers) and the access of numbers in a local addressing plan. Since numbers in non-international format are widely used in legacy fixed and mobile CS networks the seamless co-operation with these networks require the support of numbers in non-international format (including local service numbers) in the IMS. It is up to the operator's policy when and which type of numbers in non-international format can be used. In the rest of this clause the term 'visited access network' is used to indicate the network in which the user is physically located. In the case of GPRS access this is the VPLMN. In the case of other access types this is most probably the IP‑CAN provider.
The use of numbers in non-international format including local service numbers shall be provided in the following manner:
1. It shall be possible for the HPLMN to determine whether a user is using a number in non-international format according to an addressing plan used in the visited network or a geo-local service number. This shall be based upon an indication received from the UE. The same indication shall be used to access local services as well as to use a local addressing plan. This indication shall be included in the Request URI of the SIP request. If a user intends to use a number according to an addressing plan used at his/her current physical location or a local service number at his/her current physical location, then there shall be information about the visited access network independently from the location of the P‑CSCF included in the Request-URI of the SIP request.
2. The P‑CSCF shall route the session towards the S‑CSCF as per the session origination procedures.
Processing the Request URI (e.g. address analysis and potential modification such as translation into globally routable format, e.g. a globally routable PSI) shall be performed by an Application Server in the subscriber's Home Network. The S‑CSCF routes the SIP request towards this Home Network Application Server based upon filter criteria which are triggered by the information in the 'local indication' received from the UE. The AS may need to identify the visited access network, e.g. from information in SIP signalling or via the Sh interface.
When clause 4.15a (Roaming Architecture for Voice over IMS with Local Breakout) is in use and the Home Network decides to loop-back the call to the visited network and when the indication is received that the number is in accordance with the visited network numbering plan the Home network can choose to not translate numbers in non-international format and pass on the non-international number as received, to the VPLMN.
When clause 4.15b (Roaming Architecture for Voice over IMS with home routed traffic) is in use, a translation to an international routable number may be needed, but this is beyond the scope of this specification e.g. an implementation specific NNI to the VPLMN (or other 3rd party in the visited country) is needed.
3. Then the AS passes the session request back to the S‑CSCF with Request URI that contains either a globally routable SIP URI or a Tel URI with number in international format, or a Tel URI with number in non-international format if clause 4.15a (Roaming Architecture for Voice over IMS with Local Breakout) is in use and the Home network does not translate the number in non-international format. The SIP request shall contain enough information to route to the network hosting the service or using the addressing plan and allow the terminating network to identify the intended end point (e.g. service).
4. The S‑CSCF routes the SIP request, via normal IMS routing principles, towards its destination (e.g. a server in the visited access network identified by a PSI) using the Mw or Mm interfaces.
NOTE: For users who have roamed, services relevant to the locality of the user may also be provided by the home network.
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4.2.3 Support of roaming users
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The architecture shall be based on the principle that the service control for Home subscribed services for a roaming subscriber is in the Home network, e.g. the Serving‑CSCF is located in the Home network.
Figure 4.1: Service Platform in Home Network
Figure 4.2: External Service Platform
There are two possible scenarios to provide services:
- via the service platform in the Home Network
- via an external service platform (e.g. third party or visited network)
The external service platform entity could be located in either the visited network or in the 3rd party platform. The standardised way for secure 3rd party access to IMS services is via the OSA framework, see clause 4.2.4.
The roles that the CSCF plays are described below.
- The Proxy‑CSCF shall enable the session control to be passed to the Serving‑CSCF.
- The Serving‑CSCF is located in the home network. The Serving‑CSCF shall invoke service logic.
A Proxy‑CSCF shall be supported in both roaming and non-roaming case, even when the Serving‑CSCF is located in the same IM CN Subsystem.
Reassigning the Proxy‑CSCF assigned during CSCF discovery is not a requirement in this release. Procedures to allow registration time Proxy‑CSCF reassignment may be considered in future releases.
Procedures shall be supported to allow assigning different Proxy‑CSCFs when a user registers from multiple UE(s) simultaneously.
Network initiated Proxy‑CSCF reassignment is not a requirement.
The use of additional elements to be included in the SIP signalling path is optional. Such additional elements may provide functions as described in clause 4.14 and Annex I.
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4.2.4 IP multimedia Subsystem Service Control Interface (ISC)
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The ISC interface is between the Serving CSCF and the service platform(s).
An Application Server (AS) offering value added IM services resides either in the user's home network or in a third party location. The third party could be a network or simply a stand-alone AS.
The Serving‑CSCF to AS interface is used to provide services residing in an AS. Two cases were identified:
- Serving‑CSCF to an AS in Home Network.
- Serving‑CSCF to an AS in External Network (e.g. Third Party or Visited)
The SIP Application Server may host and execute services. The SIP Application Server can influence and impact the SIP session on behalf of the services and it uses the ISC interface to communicate with the S‑CSCF. The S‑CSCF shall be able to supply the AS with information to allow it to execute multiple services in order within a single SIP transaction.
The ISC interface shall be able support subscription to event notifications between the Application Server and S‑CSCF to allow the Application Server to be notified of the implicit registered Public User Identities, registration state and UE capabilities and characteristics in terms of SIP User Agent capabilities and characteristics.
The S‑CSCF shall decide whether an Application Server is required to receive information related to an incoming initial SIP request to ensure appropriate service handling. The decision at the S‑CSCF is based on (filter) information received from the HSS. This filter information is stored and conveyed on a per Application Server basis for each user. It shall be possible to include a service indication in the filter information, which is used to identify services and the order that they are executed on an Application Server within a single SIP transaction. The name(s)/address(es) information of the Application Server (s) are received from the HSS.
For an incoming SIP request, the S‑CSCF shall perform any filtering for ISC interaction before performing other routing procedures towards the terminating user, e.g. forking, caller preferences etc.
The S‑CSCF does not handle service interaction issues.
Once the IM SSF, OSA SCS or SIP Application Server has been informed of a SIP session request by the S‑CSCF, the IM SSF, OSA SCS or SIP Application Server shall ensure that the S‑CSCF is made aware of any resulting activity by sending messages to the S‑CSCF.
From the perspective of the S‑CSCF, the "SIP Application server", "OSA service capability server" and "IM-SSF" shall exhibit the same interface behaviour.
When the name/address of more than one Application Server is transferred from the HSS, the S‑CSCF shall contact the Application Servers in the order supplied by the HSS. The response from the first Application Server shall be used as the input to the second Application Server. Note that these multiple Application Servers may be any combination of the SIP Application server, OSA service capability server, or IM-SSF types.
The S‑CSCF does not provide authentication and security functionality for secure direct third party access to the IM subsystem. The OSA framework provides a standardized way for third party secure access to the IM subsystem.
If a S‑CSCF receives a SIP request on the ISC interface that was originated by an Application Server destined to a user served by that S‑CSCF, then the S‑CSCF shall treat the request as a terminating request to that user and provide the terminating request functionality as described above. Both registered and unregistered terminating requests shall be supported.
It shall be possible for an Application Server to generate SIP requests and dialogs on behalf of users. Requests originating sessions on behalf of a user are forwarded to the S‑CSCF serving the user, if the AS has knowledge of the S‑CSCF assigned to that user and the S‑CSCF shall perform regular originating procedures for these requests.
Originating requests on behalf of registered and unregistered users shall be supported.
More specifically the following requirements apply to the IMS Service control interface:
1. The ISC interface shall be able to convey charging information as per TS 32.240 [25] and TS 32.260 [26].
2. The protocol on the ISC interface shall allow the S‑CSCF to differentiate between SIP requests on Mw, Mm and Mg interfaces and SIP Requests on the ISC interface.
Figure 4.3: Void
Besides the Cx interface the S‑CSCF supports only one standardised protocol for service control, which delegates service execution to an Application Server. The protocol to be used on the ISC interface shall be SIP (as defined by IETF RFC 3261 [12], other relevant IETF RFC's and additional enhancements introduced to support 3GPP´s needs on the Mw, Mm, Mg interfaces).
The notion of a "SIP leg" used throughout this specification is identical to the notion of a call leg which is the same as a SIP dialog defined by IETF RFC 3261 [12]. The same SIP leg that is received by the S‑CSCF on the Mw, Mm and Mg interfaces is sent on the ISC interface. The same SIP leg that is received by the S‑CSCF on the ISC interface is sent on the Mw, Mm and Mg interfaces.
Concerning the relationship between the SIP legs of the ISC interface and the SIP legs of the Mw, Mm and Mg interfaces the S‑CSCF acts as a SIP proxy, as shown in Figures 4.3a – 4.3e below.
Figures 4.3a-4.3e below depict the possible high-level interactions envisioned between the S‑CSCF and the Application Server.
Figure 4.3a: Application Server acting as terminating UA, or redirect server
Figure 4.3b: Application Server acting as originating UA
Figure 4.3c: Application Server acting as a SIP proxy
Figure 4.3d: Application Server performing 3rd party call control
Figure 4.3e: A SIP leg is passed through the S‑CSCF without Application Server involvement
4.2.4a HSS to service platform Interface
The Application Server (SIP Application Server and/or the OSA service capability server and/or IM-SSF) may communicate to the HSS. The Sh and Si interfaces are used for this purpose.
For the Sh interface, the following shall apply:
1. The Sh interface is an intra-operator interface.
2. The Sh interface is between the HSS and the "SIP Application Server" and between the HSS and the "OSA service capability server". The HSS is responsible for policing what information will be provided to each individual Application Server.
3. The Sh interface transports transparent data for e.g. service related data , user related information, etc.
In this case, the term transparent implies that the exact representation of the information is not understood by the HSS or the protocol.
4. The Sh interface also supports mechanisms for transfer of user related data stored in the HSS (e.g. user service related data, MSISDN, visited network capabilities, UE Time Zone and user location information (e.g. cell global ID/Service Area ID or the address of the serving network element, VPLMN ID, etc.)). The Sh interface supports retrieving the Private User Identities using the same Public User Identity. In the case of a Public User Identity being shared across multiple Private User Identities within the same IMS subscription, the Sh interface supports the transfer of the Private User Identities that share the Public User Identity.
NOTE 1: Before providing information relating to the location of the user to a SIP Application Server, detailed privacy checks frequently need to be performed in order to meet the requirements in TS 22.071 [27]. The SIP Application Server can ensure that these privacy requirements are met by using the Le interface to the GMLC (see TS 23.271 [28]) instead of using the Sh interface.
5. The Sh interface also supports mechanisms for transfer of standardised data, e.g. for group lists, which can be accessed by different Application Servers. Those Application Servers sharing the data shall understand the data format. This enables sharing of common information between Application Servers, e.g. data managed via the Ut reference point.
6. The Sh interface also supports mechanisms that allow Application Servers to activate/deactivate their own existing initial filter criteria stored in the HSS on a per subscriber basis.
The Si interface is between the HSS and the IM-SSF. It transports CAMEL subscription information including triggers for use by CAMEL based application services.
NOTE 2: CAMEL subscription data can also be transferred from the HSS to the IM-SSF via the Sh interface.
4.2.4b S‑CSCF Service Control Model
Figure 4.3f: Service Control Model with Incoming Leg Control and Outgoing Leg Control
Figure 4.3f illustrates the relationship between the S‑CSCF and AS. It includes a first-level of modelling inside the S‑CSCF and inside the AS. To keep the model simple only one incoming leg and one outgoing leg are shown. In practice a session may consist of more than one incoming leg and/or more than one outgoing leg(s), when using User Agents. An AS may create one or more outgoing legs independent of incoming legs. An AS may create one or more outgoing legs even when there are no incoming legs.
While the above figures show session related flows, the service control model can be applied to other SIP transactions such as registration. Incoming or outgoing leg information e.g. state information, may be passed between the S‑CSCF and AS implicitly or explicitly. Implicitly means that SIP information in transit carries information about the state of the session (e.g. an INVITE message received at the S‑CSCF on an incoming leg may be sent to the AS with no changes or with some additional information). Explicitly means that SIP information is generated, e.g. to transfer state change information from an S‑CSCF to an AS in circumstances where there is no ongoing SIP transaction that can be used. It is a matter for Stage 3 design to determine when to use implicit or explicit mechanisms and to determine what extensions to SIP are necessary.
The internal model of the S‑CSCF (shown in Figure 4.3f) may sometimes exhibit proxy server like behaviour either by passing the requests to the Application Server or by passing the requests out of the system. A Proxy server may maintain session state or not. The S‑CSCF may sometimes exhibit User Agent like behaviour. Some Applications require state to be maintained in the S‑CSCF. Their exact behaviour depends on the SIP messages being handled, on their context and on S‑CSCF capabilities needed to support the services. It is a matter for Stage 3 design to determine the more detailed modelling in the S‑CSCF.
The internal model of the AS (shown in Figure 4.3f) may exhibit User Agent like behaviour. The exact behaviour depends on the SIP messages being handled and on their context. Detailed Stage 3 modelling for the AS is not required.
The definitions used in the model are:
Combined ILSM OLSM – Incoming/outgoing Leg State Model: Models the behaviour of an S‑CSCF for handling SIP messages on incoming and outgoing session legs. The Combined I/OLSM shall be able to store session state information. It may act on each leg independently, acting as a SIP Proxy, Redirect Server or User Agent dependant on the information received in the SIP request, the filter conditions specified or the state of the session.
It shall be possible to split the application handling on each leg and treat each endpoint differently.
ILCM - Incoming Leg Control Model: Models the behaviour of an S‑CSCF for handling SIP information sent to and received from an AS for an incoming session leg. The ILCM shall store transaction state information.
OLCM - Outgoing Leg Control Model: Models the behaviour of an S‑CSCF for handling SIP information received from and sent to an AS for an outgoing session leg. The OLCM shall store transaction state information.
AS-ILCM - Application Server Incoming Leg Control Model: Models AS behaviour for handling SIP information for an incoming leg. The AS-ILCM shall store Transaction State and may optionally store Session State depending on the specific service being executed.
AS-OLCM - Application Server Outgoing Leg Control Model: Models AS behaviour for handling SIP information for an outgoing leg. The AS-OLCM shall store Transaction State and may optionally store Session State depending on the specific service being executed.
4.2.4c I-CSCF to AS reference point (Ma)
The Ma reference point is between the Interrogating CSCF and the service platform(s).
The Interrogating‑CSCF to AS reference point is used to:
- forward SIP requests destined to a Public Service Identity hosted by an Application Server directly to the Application Server;
- originate a session on behalf of a user or Public Service Identity, if the AS has no knowledge of a S CSCF assigned to that user or Public Service Identity.
It shall be possible for an Application Server to originate a session on behalf of users or Public Service Identities. If the AS has no knowledge of the serving S‑CSCF for that user or Public Service Identity, such requests are forwarded to an I‑CSCF and the I CSCF shall perform regular originating procedures for these requests.
Session origination requests on behalf of registered and unregistered users shall be supported.
The Ma reference point shall be able to convey charging information according to TS 32.240 [25] and TS 32.260 [26].
The protocol to be used on the Ma reference point shall be SIP (as defined by RFC 3261 [12], other relevant IETF RFCs and additional enhancements introduced to support 3GPP´s needs on the Mw, Mm, Mg reference points).
Concerning the relationship between the SIP legs of the Ma reference point and the SIP legs of the Mw, Mm and Mg reference points the I‑CSCF acts as a SIP proxy, as shown in Figures 4.3f and 4.3g below.
Figures 4.3f and 4.3g below depict the possible high-level interactions envisioned between the I‑CSCF and the Application Server.
Figure 4.3f: I‑CSCF forwarding a SIP request destined to a Public Service Identity to an Application Server hosting this Public Service Identity
Figure 4.3g: Application Server originating a session on behalf of a user or a Public Service Identity, having no knowledge of the S‑CSCF to use
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4.2.5 The QoS requirements for an IM CN subsystem session
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The selection, deployment, initiation and termination of QoS signalling and resource allocation shall consider the following requirements so as to guarantee the QoS requirement associated with an IM CN subsystem session.
1. Independence between QoS signalling and Session Control
The selection of QoS signalling and resource allocation schemes should be independent of the selected session control protocols. This allows for independent evolution of QoS control and the session control in the IM CN subsystem.
2. Necessity for End-to-End QoS Signalling and Resource -Allocation
End-to-end QoS indication, negotiation and resource allocation during the session set-up in the IM CN subsystem should be enforced for those services and applications that require QoS better than best-effort.
3. Void.
4. Restricted Resource Access at the IP BS Level
Access to the resources and provisioning of QoS at IP BS Level should be authenticated and authorized by applying appropriate QoS policies via the IP Policy Control element
5. Restricted Resource Access at the IP-Connectivity Access Network (i.e. layer-2) Level
Access to the resources and provisioning of QoS at the IP-Connectivity Access Network Level should be authenticated and authorized by using existing registration/security/QoS policy control mechanisms of the IP‑CAN.
6. Co-ordination between Session Control and QoS Signalling/Resource Allocation
a. In establishing an IMS session, it shall be possible for an application to request that the resources needed for bearer establishment be successfully allocated before the destination user is alerted.
b. In establishing an IMS session, it shall be possible, dependent on the application being offered, to prevent the use of the bearer until the session establishment is completed.
c. In establishing an IMS session, it shall be possible for a terminating application to allow the destination user to participate in determining which bearers shall be established.
d. Successful bearer establishment shall include the completion of any required end-to-end QoS signalling, negotiation and resource allocation.
e. In establishing an IMS session, it shall be possible to use already allocated bearer resources, if these resources fulfil the needs of the session. However, note that QoS policy control mechanisms of the IP‑CAN may not allow to use already allocated bearer resources.
The initiation of any required end-to-end QoS signalling, negotiation and resource allocation processes at different network segments shall take place after the initiation and delivery of a session set-up request.
7. The Efficiency of QoS Signalling and Resource Allocation
The sequence of end-to-end QoS signalling, negotiation and resource allocation processes at different network segments should primarily consider the delay in negotiating end-to-end QoS and reserving resources that contributes to the session set-up delay. Parallel or overlapping QoS negotiation and resource reservation shall be allowed where possible.
8. Dynamic QoS Negotiation and Resource Allocation
Changes (upgrading or downgrading) of QoS provided to an active IMS session shall be supported based on either the request from the IM application or the current network loads or link quality (e.g. radio link quality).
It shall be possible to maintain a resource allocation in excess of the resources needed for current media flows (but within the restrictions imposed by points #4 and #5 above), in order to e.g. switch to different media flow characteristics without risk of admission control failure.
9. Prevention of Theft of Service
The possibility for theft of service in the IM CN subsystem shall be no higher than that for the corresponding packet data and circuit switched services.
10. Prevention of Denial of Service
The system unavailability due to denial of service attacks in the IM CN subsystem shall be no greater than that for the corresponding packet data and circuit switched services.
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4.2.6 QoS Requirements for IM CN subsystem signalling
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Depending on the bearer establishment mode, the UE or the IP‑CAN shall be able to establish a dedicated signalling IP‑CAN bearer for IM Subsystem related signalling or utilize a general-purpose IP‑CAN bearer for IM subsystem signalling traffic.
The use of a dedicated signalling IP‑CAN bearer for IM Subsystem related signalling may provide enhanced QoS for signalling traffic.
If a dedicated signalling IP‑CAN bearer is to be used for IM Subsystem related signalling, rules and restrictions may apply to the bearer according to operator implementation. A set of capabilities shall be standardised to provide user experience consistency and satisfy user expectation. The rules and restrictions on other capabilities beyond the standardised set are configured by the operator in the IP‑CAN.
To enable the described mechanism to work without requiring end-user interaction and under roaming circumstances, it is a requirement for the UE to be made aware of the rules and restrictions applied by the visited network operator. If there is no mechanism available for providing the information about the restrictions back to the UE, the available set of rules and restrictions in this Release is the set of capabilities as defined below.
The dedicated signalling IP‑CAN bearer is subject to restrictions, the capabilities to be applied are defined as follows: all messages from the UE that use a dedicated signalling IP‑CAN bearer shall have their destination restricted to:
- the P‑CSCF assigned for this UE, or to any one of the set of possible P‑CSCFs that may be assigned to this UE.
- and towards DHCP and DNS servers within the IMS operator's domain where the P‑CSCF is located.
The UE is not trusted to implement these restrictions, therefore the restrictions are enforced in the IP‑CAN by the operator.
The IP‑CAN shall be able to apply rules and restrictions for the IM CN subsystem traffic. In particular, the IP‑CAN shall be able to identify IM CN subsystem signalling traffic in order for the operator to decide on what particular rating to apply to the IM CN subsystem signalling traffic. This includes the ability to apply a special rating to at least SIP, DHCP, DNS and HTTP traffic for IMS.
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4.2.7 Support of SIP forking
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4.2.7.1 SIP Forking
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SIP forking is the ability of a SIP proxy server to fork SIP request messages to multiple destinations according to IETF RFC 3261 [12].
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4.2.7.2 Forking within and outside the IM CN Subsystem
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The IM CN subsystem shall have the capability to fork requests to multiple destinations; this capability is subject to rules for forking proxies defined in IETF RFC 3261 [12].
- The S‑CSCF shall support the ability for a Public User Identity to be registered from multiple contact addresses, as defined in IETF RFC 3261 [12]. The S‑CSCF shall support forking so that an incoming SIP request addressed to a Public User Identity is proxied to multiple registered contact addresses. This allows forking across multiple contact addresses of the same Public User Identity.
- When multiple contact addresses have been registered, then the S‑CSCF shall exhibit the following behaviour with regards to forking the incoming SIP request:
1. If the UE has indicated capability information upon IMS registration in terms of SIP User Agent capabilities and characteristics described in IETF RFC 3840 [38], then the S‑CSCF shall use it to generate a target contact set using the matching mechanism described in IETF RFC 3841 [42]. If the UE has not indicated any capabilities for the contact addresses upon registration, then the S‑CSCF may still use the preference information, if indicated for the contact addresses upon registration, as described in the following bullet point below.
2. If the UE has indicated preference information for contact addresses upon registration, then the S‑CSCF shall use it to decide if parallel or sequential forking is used across the contact addresses that have matching callee capabilities, as described in IETF RFC 3261 [12]. If the UE has not indicated any preference for the matching contact addresses upon registration, or if the preferences for the matching contact addresses have equal value, then it is up to the configuration of the S‑CSCF if parallel or sequential forking is to be performed across the contact addresses that have matching callee capabilities.
- Application Servers in the IMS shall not act as a forking proxy towards the S‑CSCF in the sense of IETF RFC 3261 [12].
NOTE 1: The AS may subscribe to the registration event package to retrieve the contact address(es) of the UE. Based on this information the AS may act as a forking proxy in the sense of IETF RFC 3261 [12] towards other nodes than the S‑CSCF.
NOTE 2: The AS may initiate multiple requests towards the registered Public User Identities of a user, however, this is not considered as forking in the sense of IETF RFC 3261 [12].
Additionally, other networks outside the IM CN Subsystem are able to perform SIP forking.
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4.2.7.3 Support for forked requests
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UE and MGCF shall be ready to receive responses generated due to a forked request and behave according to the procedures specified in IETF RFC 3261 [12] and in this clause.
The UE and MGCF may accept or reject early dialogues from different terminations as described in IETF RFC 3261 [12], for example if the UE is only capable of supporting a limited number of simultaneous dialogs.
Upon the reception of a first final 200 OK (for INVITE), the UE or MGCF shall acknowledge the 200 OK. In addition the UE or MGCF may require updating the allocated resources according to the resources needed. If the UE or MGCF receives a subsequent 200 OK, the UE or MGCF shall acknowledge the dialogue and immediately send a BYE to drop the dialog.
NOTE: Upon the reception of a first final 200 OK (for INVITE), the UE or MGCF may terminate the early dialogue, as specified in IETF RFC 3261 [12].
The UE and MGCF may include preferences according to IETF RFC 3841 [42], in INVITE's, indicating that proxies should not fork the INVITE request. The S‑CSCF and AS should follow the preferences, if included in the INVITE request. On the terminating side, UE and MGCF shall be able to receive, as specified in IETF RFC 3261 [12], several requests for the same dialog that were forked by a previous SIP entity.
Application Servers and MRFCs shall be capable to handle forked requests according to the procedures specified in IETF RFC 3261 [12].
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4.3 Naming and addressing concepts
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4.3.1 Address management
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The mechanisms for addressing and routing for access to IM CN subsystem services and issues of general IP address management are discussed in TS 23.221 [7].
When a UE is assigned an IPv6 prefix, it can change the global IPv6 address it is currently using via the mechanism defined in IETF RFC 4941 [16a], or similar means. When a UE is registered in the IM CN Subsystem with an IP address, any change to this IP address that is used to access the IM CN subsystem will result in dropping the active SIP dialogs and shall trigger automatic registration. This automatic registration updates the UE's IP address and security association. To avoid disruption of ongoing IM CN subsystem services, the UE should not change the IP address that it uses to access the IM CN subsystem while engaged in active SIP dialogs (e.g. INVITE or SUBSCRIBE-NOTIFY dialogs).
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4.3.2 Void
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Figure 4.4: Void
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4.3.3 Identification of users
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4.3.3.0 General
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There are various identities that may be associated with a user of IP multimedia services. This clause describes these identities and their use.
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4.3.3.1 Private User Identities
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Every IM CN subsystem user shall have one or more Private User Identities. The private identity is assigned by the home network operator and used, for example, for Registration, Authorization, Administration and Accounting purposes. This identity shall take the form of a Network Access Identifier (NAI) as defined in IETF RFC 4282 [14]. It is possible for a representation of the IMSI to be contained within the NAI for the private identity.
- The Private User Identity is not used for routing of SIP messages.
- The Private User Identity shall be contained in all Registration requests, (including Re-registration and De-registration requests) passed from the UE to the home network.
- An ISIM application shall securely store one Private User Identity. For UEs supporting only non-3GPP accesses or UEs accessing IMS via SNPN, if neither ISIM nor USIM is present, but IMC is present, the Private User Identity shall be stored in IMC. It shall not be possible for the UE to modify the Private User Identity information stored on the ISIM application or IMC.
- The Private User Identity is a unique global identity defined by the Home Network Operator, which may be used within the home network to identify the user's subscription (e.g. IM service capability) from a network perspective. The Private User Identity identifies the subscription, not the user.
- The Private User Identity shall be permanently allocated to a user's subscription (it is not a dynamic identity) and is valid for the duration of the user's subscription with the home network.
- The Private User Identity is used to identify the user's information (for example authentication information) stored within the HSS (for use for example during Registration).
- The Private User Identity may be present in charging records based on operator policies.
- The Private User Identity is authenticated only during registration of the user, (including re-registration and de-registration).
- The HSS needs to store the Private User Identity.
- The S‑CSCF needs to obtain and store the Private User Identity upon registration and unregistered termination.
- If mobile terminated short message service without MSISDN as defined in TS 23.204 [56] is required then the Private User Identity shall be based on the IMSI according to TS 23.003 [24], clause 13.3.
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4.3.3.2 Public User Identities
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Every IM CN subsystem user shall have one or more Public User Identities (see TS 22.228 [8]), including at least one taking the form of a SIP URI (see IETF RFC 3261 [12]). The Public User Identity is used by any user for requesting communications to other users. For example, this might be included on a business card.
- Both telecom numbering and Internet naming schemes can be used to address users depending on the Public User identities that the users have.
- The Public User Identity shall take the form as defined in TS 23.003 [24].
- An ISIM application shall securely store at least one Public User Identity. For UEs supporting only non-3GPP accesses or UEs accessing IMS via SNPN, if neither ISIM nor USIM is present, but IMC is present, the Public User Identity shall be stored in IMC. It shall not be possible for the UE to modify the Public User Identity, but it is not required that all additional Public User Identities be stored on the ISIM application or IMC.
- A Public User Identity shall be registered either explicitly or implicitly before originating IMS sessions and originating IMS session unrelated procedures can be established by a UE using the Public User Identity. Subscriber-specific services for unregistered users may nevertheless be executed as described in clause 5.6.5. Each implicit registration set shall contain at least one Public User Identity taking the form of a SIP URI.
NOTE: An implicit registration set can contain Public User Identities of more than one service profile. When sending a third party registration request (for details see clause 5.4.1.7 in TS 24.229 [10a]) to an AS based on an initial filter criteria in a service profile, the third party registration request will include a Public User Identity taking the form of a SIP URI from that service profile within the implicit registration set.
- It shall be possible to identify Alias Public User Identities. For such a group of Public User Identities, operations that enable changes to the service profile and the service data configured shall apply to all the Public User Identities within the group. This grouping information shall be stored in the HSS. It shall be possible to make this grouping information available to the AS via the Sh interface and Sh operations are applicable to all of the Public User Identities within the same Alias Public User Identity group. It shall be possible to make this information available to the S‑CSCF via the Cx interface. It shall be possible to make this information available to the UE via the Gm interface.
- A Public User Identity shall be registered either explicitly or implicitly before terminating IMS sessions and terminating IMS session unrelated procedures can be delivered to the UE of the user that the Public User Identity belongs to. Subscriber-specific services for unregistered users may nevertheless be executed as described in clause 5.12.
- It shall be possible to register globally (i.e. through one single UE request) a user that has more than one public identity via a mechanism within the IP multimedia CN subsystem (e.g. by using an Implicit Registration Set). This shall not preclude the user from registering individually some of his/her public identities if needed.
- Public User Identities are not authenticated by the network during registration.
- Public User Identities may be used to identify the user's information within the HSS (for example during mobile terminated session set-up).
4.3.3.2a Globally Routable User Agent URI (GRUU)
A Globally Routable User Agent URI (GRUU) is an identity that identifies a unique combination of Public User Identity and UE instance that allows a UE to address a SIP request to a specific Public User Identity UE combination instance, as opposed to a Public User Identity, in order to ensure that the SIP request is not forked to another registered UE of the same Public User Identity. There are two types of GRUUs; Public GRUUs (P‑GRUUs) and Temporary GRUUs (T‑GRUUs). P‑GRUUs are GRUUs that reveal the Public User Identity of the user and are very long lived. T‑GRUUs are GRUUs that contain a URI that do not reveal the Public User Identity of the user and are valid until the contact is explicitly de-registered or the current registration expires. The IM CN subsystem shall support the capability for IMS UEs to obtain both T‑GRUUs and P‑GRUUs when performing IMS registration, exchange GRUUs using SIP requests and responses and use GRUUs to address SIP requests to specific UEs according to RFC 5627 [49].
4.3.3.2a.1 Architecture Requirements
The following architectural requirements shall apply to support of GRUU in the IMS:
0. If a UE could become engaged in a service (e.g. telephony supplementary service) that potentially requires the ability to identify and interact with a specific UE even when multiple UEs share the same single Public User Identity then the UE should support GRUU.
1. A GRUU shall be registered in the IMS network with a unique combination of specific Public User Identity and UE.
2. If a UE supports GRUU, it shall indicate support for a GRUU that is associated with a specific Public User Identity at the time of registration of the Public User Identity. The UE shall use the same instance ID for all registration requests regardless of the access network used for registration. A function that registers on behalf of a UE shall use the same Instance ID as if that UE had performed the registration itself.
NOTE 1: If the UICC is replaced the UE is still considered to be same UE instance and so the UE instance ID is not changed by using a different UICC.
3. The IMS network shall be able to receive an indication of support for GRUU for a specific Public User Identity at a specific UE instance and be able to generate both P‑GRUU's and T‑GRUU's and return them back to the UE that indicated support for GRUU.
NOTE 2: The UE may have a registration request that indicates GRUU support, but the GRUU will not be returned if IMS network does not support generation of GRUUs.
4. When the IMS network receives indication of GRUU support for a specific Public User Identity from the UE during a registration request, the IMS network shall also generate P‑GRUU's and T‑GRUU's for all implicitly registered Public User Identities belonging to the same implicit registration set. The IMS network shall communicate all these other GRUUs to the UE.
5. Registrations of all GRUUs associated with a specific Public User Identity shall also be directed to the same S‑CSCF.
6. The IMS network will be able to generate GRUU's for any UE registered with a valid SIP URI.
7. The IMS network shall generate the same P‑GRUU for a given Public User Identity and Instance Identifier combination.
8. The IMS network shall generate a different T‑GRUU for a given Public User Identity and Instance Identifier combination for each registration and re-registration.
9. The IMS network shall be able to derive the Public User Identity directly from the P‑GRUU. The Public User Identity derived from the P‑GRUU used to identify the contact address of the sender shall be same as the Public User Identity used to identify the initiator or an associated Public User Identity. If the URI in the SIP Contact header of the sender carries a parameter indicating that it is a GRUU but does not comply with the stated requirement or if there is no registration corresponding to the GRUU, then the IMS network should reject the request.
10. The IMS network shall be able to route requests destined to a GRUU to the UE instance registered with that GRUU.
11. The IMS network shall not fork SIP requests addressed to a GRUU to separate UEs.
12. A UE that is capable of supporting GRUUs shall be able to differentiate between a GRUU and a Public User Identity.
13. The IMS network shall support establishment of session or non-session related communication using a GRUU.
14. A UE supporting GRUUs shall be able to inter-work with an IMS network not supporting GRUUs.
15. A UE supporting GRUUs shall be able to inter-work with a UE not supporting GRUUs per RFC 5627 [49].
16. A UE or network that supports GRUUs shall not negatively affect networks or UEs that do not support GRUUs.
17. It shall be possible to define iFCs that match the Public User Identity part of a GRUU.
18. It shall be possible for iFCs to determine whether the Request URI of a message contains a GRUU and then trigger to Application Servers that are only applicable for GRUUs.
19. It shall be possible to provide terminating services to a GRUU associated with a currently unregistered subscriber.
NOTE 3: The network may not be able to validate the unregistered GRUU of a currently unregistered or registered subscriber, such that operator policy might restrict the services available to the GRUU under these conditions.
20. It shall be possible to apply same level of privacy irrespective whether GRUU is used or not.
4.3.3.2b Wildcarded Public User Identity
It shall be possible to support a wildcarded Public User Identity. A wildcarded Public User Identity expresses a set of Public User Identities grouped together. It shall be possible to include and express the wildcarded Public User Identity in the implicit registration set according to clause 5.2.1a.
Only distinct Public User Identities shall be used for explicit registration. The implicit registration of a wildcarded Public User Identity shall be handled in the same manner as the implicit registration of a distinct Public User Identity from a network perspective, with only one service profile associated to the wildcarded Public User Identity.
It shall be possible for a user to have a distinct Public User Identity even if it matches a wildcarded Public User Identity. Such a distinct Public User Identity may have a different service profile than the wildcarded Public User Identity.
Editor's note: It is to TBD if a distinct Public User Identity shall be included in the same implicit registration or not. If stage 3 protocol solution found for this issue, then they can be in separate implicit registration set.
The matching of a distinct Public User Identity shall take precedence over matching of wildcarded Public User Identity. When the value of a Public User Identity matches what is expressed as an implicitly registered wildcarded Public User Identity and there is no better match, then the procedures are the same as in the case that the identifier matches an implicitly registered distinct Public User Identity.
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4.3.3.3 Routing of SIP signalling within the IP multimedia subsystem
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Routing of SIP signalling within the IMS shall use SIP URIs or other (non SIP) AbsoluteURIs. AbsoluteURIs are defined in IETF RFC 3986 [13]. Routing of SIP signalling within the IMS using AbsoluteURI (non SIP) shall only be supported for IMS signalling from IMS user to external networks. E.164 [2] format Public User Identities shall not be used for routing within the IMS and session requests based upon E.164 format Public User Identities will require conversion into SIP URI format for internal IMS usage.
4.3.3.3a Handling of dialled number formats
When using a phone number as the dialled address, the UE can provide this number in the form of a SIP URI or a TEL URI. This phone number can be in the form of E.164 format (prefixed with a '+' sign), or a local format using local dialling plan and prefix. The IMS will interpret the phone number with a leading '+' to be a fully defined international number.
4.3.3.3b Termination of session with the TEL URI format Public User Identity
If a terminating session with a TEL URI is used, the HSS and the SLF (in the case that more than one independently addressable HSS is utilized by a network operator) shall support the TEL URI format Public User Identity.
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4.3.3.4 Relationship of Private and Public User Identities
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The home network operator is responsible for the assignment of the Private User Identities and Public User Identities; other identities that are not defined by the operator may also exist.
Figure 4.5: Relationship of the Private User Identity and Public User Identities
The IMS Service Profile is a collection of service and user related data as defined in TS 29.228 [30]. The Service Profile is independent from the Implicit Registration Set, e.g. Public User Identities with different Service Profiles may belong to the same Implicit Registration Set. Initial filter criteria in the service profile provide a simple service logic comprising of user / operator preferences that are of static nature i.e. they do not get changed on a frequent basis. It shall be possible to identify Alias Public User Identities. See clause 4.3.3.2 for more details.
Application servers will provide more complex and dynamic service logic that can potentially make use of additional information not available directly via SIP messages (e.g. location, time, day etc.).
The IMS service profile is defined and maintained in the HSS and its scope is limited to IM CN Subsystem. A Public User Identity shall be registered at a single S‑CSCF at one time. All Public User Identities of an IMS subscription shall be registered at the same S‑CSCF. The service profile is downloaded from the HSS to the S‑CSCF. Only one service profile shall be associated with a Public User Identity at the S‑CSCF at a given time. Multiple service profiles may be defined in the HSS for a subscription. Each Public User Identity is associated with one and only one service profile. Each service profile is associated with one or more Public User Identities.
An ISIM application shall securely store the home domain name of the subscriber. For UEs supporting only non-3GPP accesses or UEs accessing IMS via SNPN, if neither ISIM nor USIM is present, but IMC is present, the home domain name shall be stored in IMC. It shall not be possible for the UE to modify the information from which the home domain name is derived.
It is not a requirement for a user to be able to register on behalf of another user which is third party registration specified in IETF RFC 3261 [12] or for a device to be able to register on behalf of another device or for combinations of the above for the IM CN subsystem for this release.
Public User Identities may be shared across multiple Private User Identities within the same IMS subscription. Hence, a particular Public User Identity may be simultaneously registered from multiple UEs that use different Private User Identities and different contact addresses. If a Public User Identity is shared among the Private User Identities of a subscription, then it is assumed that all Private User Identities in the IMS subscription share the Public User Identity.
The relationship for a shared Public User Identity with Private User Identities and the resulting relationship with service profiles and IMS subscription, is depicted in Figure 4.6.
An IMS subscription may support multiple IMS users.
NOTE 1: The Public User Identity sharing mechanism described above is not intended to support sharing of identities across large numbers of Private User Identities, since this would result in all these users being forced to be associated with the same IMS subscription and hence the same S‑CSCF.
NOTE 2: Subscription data is assumed to indicate which Public User Identities within a subscription are shared and which are not.
Figure 4.6: The relation of a shared Public User Identity (Public-ID-2) and Private User Identities
All Service Profiles of a user shall be stored in the same HSS, even if the user has one or more shared Public User Identities.
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4.3.3.5 Relationship of Public User Identities, GRUUs and UEs
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Each Public User Identity may have one or more Globally Routable User Agent URIs (GRUUs). There are two types of GRUU, P‑GRUUs and T‑GRUUs which are associated with Public User Identities and are generated and assigned to the UE together during registrations and re-registration in a pair of one P‑GRUU and one T‑GRUU. Each pair of a P‑GRUU and a T‑GRUU is associated with one Public User Identity and one UE. During subsequent re-registrations the same P‑GRUU will be assigned to the UE but a new and different T‑GRUU will be generated and assigned. After a re-registration all the previous T‑GRUUs generated during the period of this registration are all still valid. A UE may retain some or all of the previous T‑GRUUs obtained during the initial registration or previous re-registrations along with the new T‑GRUU or the UE may replace some or all of the previous T‑GRUUs with the new T‑GRUU. The current set of the P‑GRUU and all T‑GRUUs which are currently valid during this registration period is referred to here as the GRUU set. This relationship is depicted in figure 4.6a. If a UE registers (explicitly or implicitly) with multiple Public User Identities, a separate GRUU set is associated with each. If different UEs register with the same Public User Identity, a different GRUU set is associated with each.
NOTE: If the UICC is replaced the UE is still considered to be same UE instance and if that UE instance with a different UICC registers the same Public User Identity as was registered with the previous UICC the same P-GRUU will be assigned for that Public User Identity UE instance combination.
Figure 4.6a: The relationship of Public User Identities, GRUUs and UEs
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4.3.4 Identification of network nodes
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The CSCF, BGCF and MGCF nodes shall be identifiable using a valid SIP URI (Host Domain Name or Network Address) on those interfaces supporting the SIP protocol, (e.g. Gm, Mw, Mm and Mg). These SIP URIs would be used when identifying these nodes in header fields of SIP messages. However this does not require that these URIs will be globally published in DNS.
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4.3.5 E.164 address to SIP URI resolution in an IM CN subsystem
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4.3.5.1 ENUM/DNS translation mechanism
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The ENUM/DNS translation mechanism as specified in IETF RFC 3761 [16] can be used by all IMS nodes that require E.164 address to SIP URI resolution. The actual ENUM/DNS database(s) used to perform address translations are outside the scope of 3GPP and are therefore a matter for the network operator. There is no requirement that the universal ENUM service on the Internet be used. As such, it is possible that the ENUM/DNS mechanism uses a different top level domain to that of "e164.arpa." (as mandated in IETF RFC 3761 [16], clause 1.2), therefore, the top level domain to be used for ENUM domain names shall be a network operator configurable option in all IMS nodes that can perform ENUM/DNS resolution.
In some scenarios, owners of ENUM servers may require information on who is the querying IMS operator, to determine an appropriate response (including whether to respond at all). This capability is required on the egress of the IMS network, particularly in the presence of shared network elements and intermediary IMS network(s) between the originating IMS operator and target ENUM/DNS server(s).
ENUM databases may contain Number Portability information. Number Portability is further described in clause 4.18.1.
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4.3.5.2 Handling of Tel URIs
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The S‑CSCF shall support the ability to translate the E.164 address contained in a Request-URI in the Tel: URI format (as specified in IETF RFC 3966 [15]) to a SIP routable SIP URI using the ENUM/DNS translation mechanism as specified in clause 4.3.5.1. If this translation succeeds, then the session shall be routed according to the returned SIP URI. If this translation fails, then the session may be forwarded to a BGCF for further routing (e.g. to the PSTN) as described in clause 5.19 or appropriate notification shall be sent to the originating session endpoint, depending on network operator configuration.
When clause 4.15a (Roaming Architecture for Voice over IMS with Local Breakout) is in use and the Home Network decides to loop-back the call to the visited network, the Home network can choose not to translate the E.164 address in the Request URI to a globally routable SIP URI and leave it to the visited network.
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4.3.5.3 Handling of SIP URIs representing a telephone number
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Per network operator policy, the network may attempt to resolve and route a SIP URI representing a telephone number and a domain that does not own the target user using the ENUM/DNS translation mechanism specified in clause 4.3.5.1. The need for address resolution may be triggered by the S‑CSCF and the I‑CSCF or transit function, as determined by network operator configuration. Procedures applied to the S‑CSCF, I‑CSCF and transit functions are outlined below.
When an originating S‑CSCF receives an originating request with a Request-URI containing the SIP representation of an E.164 number, network operator policy shall dictate whether the procedure shall be carried out for all the domains of the SIP URI where those domains belong to the home network, or not at all. If operator policy indicates that the procedure is to be performed, then the S‑CSCF shall reuse the procedure specified in clause 4.3.5.for handling of Tel URIs.
If the operator policy at the originating S‑CSCF dictates that the procedure shall not be performed or the SIP URI containing the representation of an E.164 number contains a domain that does not belong to the home network, then the S‑CSCF shall handle and route the request in the same manner as a SIP URI.
Prior to an HSS Location Query, the I‑CSCF shall translate a SIP URI representing a telephone number contained in a Request‑URI into the Tel: URI format specified in IETF RFC 3966 [15]. The resultant Tel URI shall then be used for performing the HSS Location Query.
If the HSS Location Query response indicates that the user does not exist and if configured by operator policy, the I‑CSCF shall invoke the portion of transit functionality that translates the E.164 address contained in the Tel URI in the Request‑URI into a routable SIP URI, reusing the procedure specified in 4.3.5.2 for handling of Tel URIs.
NOTE: The entire transit functionality is not required for this purpose.
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4.3.6 Public Service Identities
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With the introduction of standardized presence, messaging, conferencing and group service capabilities in IM CN subsystem, there is a need for Public Service Identities (PSIs). These identities are different from the Public User Identities in the respect that they identify services, which are hosted by Application Servers. In particular, Public Service Identities are used to identify groups, see clause 4.10. For example a chat-type service may use a Public Service Identity (e.g. sip:[email protected]) to which the users establish a session to be able to send and receive messages from other session participants. As another example, local service may be identified by a globally routable Public Service Identity.
Public Service Identities shall take the form as defined in TS 23.003 [24].
The IM CN subsystem shall provide the capability for users to create, manage and use Public Service Identities under control of AS. It shall be possible to create statically and dynamically a Public Service Identity.
Each Public Service Identity is hosted by an Application Server, which executes the service specific logic as identified by the Public Service Identity.
The IM CN Subsystem shall provide capability of routing IMS messages using Public Service Identity.
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4.4 Signalling concepts
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A Single session control between the UE and CSCF:
- For Multi-Media type services delivered via the IP‑CAN within this architecture, a single session control protocol shall be used between the user equipment UE and the CSCF (over the Gm reference point).
Protocols over the Gm reference point :
- The single protocol applied between the UE and CSCF (over the Gm reference point) within this architecture will be based on SIP (as defined by IETF RFC 3261 [12], other relevant IETF RFC's and additional enhancements required to support 3GPP's needs).
A Single session control on the Mw, Mm, Mg, Mi, Mj, Mk, Mx:
- A single session control protocol shall be used on the session control interfaces between:
- MGCF and CSCF (Mg),
- between CSCFs (Mw),
- between a CSCF/IMS ALG and external IP networks (Mm),
- between CSCF and BGCF (Mi),
- between BGCF and MGCF (Mj),
- between BGCF/IMS ALG and BGCF (Mk) and
- between BGCF/CSCF and IBCF (Mx).
Protocols for the Mw, Mm, Mg, Mi, Mj, Mk, Mx:
- The single session control protocol applied to these interfaces will be based on SIP (as defined by IETF RFC 3261 [12], other relevant IETF RFC's and additional enhancements required to support 3GPP´s needs).
UNI vs. NNI session control :
- The SIP based signalling interactions between CN elements may be different than SIP based signalling between the UE and the CSCF.
Based on operator preference, border control functions may be applied between two IM CN subsystem networks or between an IM CN subsystem network and other SIP based multimedia network, see clause 4.14 and Annex I for details.
Restrict access from external networks :
- The signalling solution shall allow the operator to restrict access from external networks (application level).
Access to HSS :
- A network operator can control access to the HSS.
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4.5 Mobility related concepts
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The following procedures are supported by an UE when accessing IMS:
- Connect to the IP‑CAN and acquire the necessary IP address, which includes, or is followed by, the P‑CSCF discovery procedure. The mobility related procedures and IP address management principles for the IP‑CAN are described in the relevant IP‑CAN specifications;
- Register to the IM subsystem as defined by the IMS registration procedures;
- If an UE explicitly deactivates the IP‑CAN bearer that is being used for IMS signalling, it shall first de-register from the IMS (while there is no IMS session in progress);
- If an UE explicitly deactivates the IP‑CAN bearer that is being used for IMS signalling while an IMS session is in progress, the UE must first release the session and de-register from the IMS and then deactivate the IP‑CAN bearers;
- If an UE changes its IP address according to IP‑CAN procedures (e.g. TS 23.221 [7]), the UE shall re- register in the IMS by executing the IMS registration;
- If an UE acquires an additional IP address due to establishing an additional IP‑CAN bearer through a different access network, the UE may perform an IMS registration using this IP address as the contact address. If IMS registration is performed, this IMS registration may co-exist with the previous IMS registration from this UE and the UE shall be notified that this IMS registration results in multiple simultaneous registrations.
- In order to be able to deliver an incoming IMS session, the IP‑CAN bearer that is being used for IMS signalling need to remain active as long as the UE is registered in the IM CN subsystem;
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4.6 Roles of Session Control Functions
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4.6.0 General
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The CSCF may take on various roles as used in the IP multimedia subsystem. The following clauses describe these various roles.
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4.6.1 Proxy‑CSCF
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The Proxy‑CSCF (P‑CSCF) is the first contact point within the IM CN subsystem. Its address is discovered by UEs using the mechanism described in the clause "Procedures related to Local CSCF Discovery". The P‑CSCF behaves like a Proxy (as defined in IETF RFC 3261 [12] or subsequent versions), i.e. it accepts requests and services them internally or forwards them on. The P‑CSCF shall not modify the Request URI in the SIP INVITE message. The P‑CSCF may behave as a User Agent (as defined in the IETF RFC 3261 [12] or subsequent versions), i.e. in abnormal conditions it may terminate and independently generate SIP transactions.
NOTE 1: When requests are sent towards another domain they may, if required, be routed via a local network exit point (IBCF), which will then forward the request to the entry point of the other domain. More details on this can be found in clause 4.14 and Annex I.
The P-CSCF in the role of an AF may interact with the Policy and Charging Architecture; the P-CSCF may interact over the Rx interface (see TS 29.214 [11]) with the Policy and Charging Architecture defined in TS 23.203 [54]; the P-CSCF may interact over the Rx interface (see TS 29.214 [11]) or over the N5 interface (using the Npcf_PolicyAutorization service, see TS 29.514 [96]) with the Policy and Charging Architecture defined in TS 23.503 [95].
The functions performed by the P‑CSCF are:
- Forward the SIP register request received from the UE to an entry point determined using the home domain name, as provided by the UE.
- Forward SIP messages received from the UE to the SIP server (e.g. S‑CSCF) whose name the P‑CSCF has received as a result of the registration procedure.
- Ensure that the SIP messages received from the UE to the SIP server (e.g. S‑CSCF) contain the correct or up to date information about the access network type currently used by the UE, when the information is available from the access network. Depending on operator policies, the P‑CSCF may insert in any SIP message (request or response) the access network type currently used by the UE, when the information is available from the access network.
NOTE 2: For the 3GPP access network, the P‑CSCF can derive information about the access network type currently used by the UE using PCC mechanisms as specified in TS 23.203 [54] and in TS 29.214 [11], or in TS 23.503 [95] and in TS 29.514 [96].
NOTE 3: IMS entities other than P‑CSCF will not be informed by this mechanism of the change in the access network unless SIP messages are exchanged.
- Based on operator policies and the availability of the user location information and/or UE Time Zone from the access network, ensure that relevant SIP messages contain the correct or up to date information about the user location information and/or UE Time Zone provided by the access network currently used by the UE.
NOTE 4: For the 3GPP access networks and for TWAN access (as defined in clause 16 of TS 23.402 [82]), the P‑CSCF can retrieve user location information and/or UE Time Zone related to the access network currently used by the UE using PCC mechanisms, as specified in TS 23.203 [54] and in TS 29.214 [11], or in TS 23.503 [95] and in TS 29.514 [96].
- Forward the SIP request or response to the UE.
Detect and handle an emergency session establishment request.
- Generation of CDRs.
- Maintain a Security Association between itself and each UE, as defined in TS 33.203 [19].
- Should perform SIP message compression/decompression.
- Authorization of bearer resources and QoS management. For details see TS 23.203 [54] and TS 23.503 [95].
- Handling of Resource-Priority information.
- Detection and handling of:
- an originating or terminating IMS MPS session establishment or session modification request;
- MPS for Messaging;
(see also clause 5.21).
- May support the Paging Policy Differentiation for IMS conversational voice as described in clause E.9 and clause Y.9.
- May subscribe to notification of changes in the type of access network using PCC mechanisms as specified in TS 23.203 [54] and in TS 29.214 [11] or in TS 23.503 [95] and in TS 29.514 [96].
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4.6.2 Interrogating‑CSCF
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4.6.2.0 General
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Interrogating‑CSCF (I‑CSCF) is the contact point within an operator's network for all connections destined to a user of that network operator, or a roaming user currently located within that network operator's service area.
NOTE- 1: If border control concepts are applied, the contact point within an operator's network may be different, see clause 4.14 and Annex I for details.
NOTE 2: When requests are sent towards another domain they may, if required, be routed via a local network exit point (IBCF), which will then forward the request to the entry point of the other domain. More details on this can be found in clause 4.14 and Annex I.
There may be multiple I‑CSCFs within an operator's network. The functions performed by the I‑CSCF are:
Registration
- Assigning a S‑CSCF to a user performing SIP registration (see the clause on Procedures related to Serving‑CSCF assignment)
Session-related and session-unrelated flows
- Route a SIP request received from another network towards the S‑CSCF.
- Translate the E.164 address contained in all Request‑URIs having the SIP URI with user=phone parameter format into the Tel: URI format of IETF RFC 3966 [15] before performing the HSS Location Query. In the event the user does not exist and if configured by operator policy, the I‑CSCF may invoke the portion of the transit functionality that translates the E.164 address contained in the Request‑URI of the Tel: URI format to a routable SIP URI.
- Obtain from HSS the Address of the S‑CSCF.
- Forward the SIP request or response to the S‑CSCF determined by the step above
Based on local configuration, the I‑CSCF may perform transit routing functions (see clause 5.19). If the I‑CSCF determines, based on an HSS query, that the destination of the session is not within the IMS, it may forward the request or it may return with a failure response toward the originating endpoint.
Charging and resource utilisation:
- Generation of CDRs.
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4.6.2.1 Void
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4.6.3 Serving‑CSCF
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The Serving‑CSCF (S‑CSCF) performs the session control services for the UE. It maintains a session state as needed by the network operator for support of the services. Within an operator's network, different S‑CSCFs may have different functionalities. The functions performed by the S‑CSCF during a session are:
For Registration:
- May behave as a Registrar as defined in IETF RFC 3261 [12] or subsequent versions, i.e. it accepts registration requests and makes its information available through the location server (e.g. HSS).
- When a registration request includes an Instance ID with the contact being registered and indicates support for GRUU, the S‑CSCF shall assign a unique P‑GRUU and a new and unique T‑GRUU to the combination of Public User Identity and Instance ID.
- If a registration request indicates support for GRUU, the S‑CSCF shall return the GRUU set assigned to each currently registered Instance ID.
- The S‑CSCF shall notify subscribers about registration changes, including the GRUU sets assigned to registered instances.
- During registration process, the S-CSCF shall provide policy information, if available, for a Public User Identity from the HSS to the P-CSCF and/or UE.
NOTE 1: For example, the policy information includes MPS IMS Subscription status and policy applicable to enterprise network subscribers.
For Session-related and session-unrelated flows:
- Session control for the registered endpoint's sessions. It shall reject IMS communication to/from Public User Identity(s) that are barred for IMS communications after completion of registration, as described in clause 5.2.1.
- May behave as a Proxy Server as defined in IETF RFC 3261 [12] or subsequent versions, i.e. it accepts requests and services them internally or forwards them on, possibly after translation.
- May behave as a User Agent as defined in IETF RFC 3261 [12] or subsequent versions, i.e. it may terminate and independently generate SIP transactions.
- Based on the determined served user, handle interaction with Services Platforms for the support of Services
- Provide endpoints with service event related information (e.g. notification of tones/announcement together with location of additional media resources, billing notification)
- For an originating endpoint (i.e. the originating user/UE, or originating AS)
- Obtain from a database the Address of the entry point for the network operator serving the destination user from the destination name (e.g. dialled phone number or SIP URI), when the destination user is a customer of a different network operator and forward the SIP request or response to that entry point.
If a GRUU is received as the contact, ensures that the Public User Identity of the served user in the request and the Public User Identity encapsulated in the P‑GRUU or associated with the T‑GRUU belongs to the same service profile.
- When the destination name of the destination user (e.g. dialled phone number or SIP URI) and the originating user is a customer of the same network operator, forward the SIP request or response to an I‑CSCF within the operator's network.
- Depending on operator policy, forward the SIP request or response to another SIP server located within an ISP domain outside of the IM CN subsystem.
- Forward the SIP request or response to a BGCF for call routing to the PSTN or CS Domain.
- Ensure the originating end point is subscribed to the determined IMS communication service.
- Ensure that the content of the SIP request or response (e.g. value included in Content-Type SIP header, media lines included in SDP) sent or received by the originating endpoint matches the determined IMS communication service definition, based on originating user's subscription.
- When the INVITE message includes an MPS code or an MPS input string, forward the INVITE, including the Service User's priority level if available.
- When an MPS user is authorized by an AS for priority service, include the Service User's priority level received from the AS in the INVITE and forward the INVITE.
NOTE 2: The mechanism to provide authorisation by an AS for priority service is out of scope of this specification.
- Attestation of the identity of the originating subscriber if configured through operator policies. Optionally the S-CSCF may invoke an AS for attestation of the identity of originating subscriber, if configured through operator policies.
- Optionally the S-CSCF may invoke an AS for attestation of the RCD information or RCD URL of originating subscriber, if configured through operator policies as per Annex AF.
NOTE 3: Only one network element performs attestation for an originating subscriber in the originating network.
- Assertion of authorization for the Resource-Priority information for an IMS priority session if configured through operator policies. Optionally, the S-CSCF can invoke an AS for assertion and signing of the authorization for the Resource-Priority information for the IMS priority session, if configured through operator policies.
- If the request is an originating request from an Application Server:
- Verify that the request coming from the AS is an originating request, determine the served user and apply procedures accordingly (e.g. invoke interaction with Service Platforms for originating services, etc.).
- Process and proceed with the request even if the served user on whose behalf the AS had generated the request is unregistered. If the served user is unregistered, the S‑CSCF shall execute any unregistered origination service logic on behalf of the served user before forwarding requests from an AS.
- Process and proceed with other requests to and from the served user on whose behalf the AS had generated the request.
- Reflect in the charging information that an AS has initiated the session on behalf of a served user.
- For a destination endpoint (i.e. the terminating user/UE)
- Forward the SIP request or response to a P‑CSCF.
- Modify the SIP request for routing an incoming session to CS domain according to HSS and service control interactions, if the user is to receive the incoming session via the CS domain.
- Forward the SIP request or response to a BGCF for call routing to the PSTN or the CS domain.
- Ensure the terminating end point is subscribed to the determined IMS communication service.
- Ensure that the content of SIP request or response (e.g. value included in Content-Type SIP header, media lines included in SDP) sent or received by the destination end point matches the determined IMS communication service definition, based on terminating user's subscription.
- If the SIP request contains preferences for characteristics of the destination endpoint, perform preference and capability matching as specified in IETF RFC 3312 [41].
- In addition and if configured through operator policies, the S-CSCF may perform signature verification of the RCD information or RCD URL of the originating subscriber for terminating requests, if a signature is included as per Annex AF.
- Optionally for a redirected session, if configured through operator policies, performs attestation of the identity of the diverting subscriber initiating the diversion.
- Proxies a terminating request to an AS associated with the terminating user for signature verification if signature verification is required.
NOTE 4: The S-CSCF would normally proxy any terminating request to an AS via ISC for additional processing.
- For an originating request with a Request URI containing the SIP representation of an E.164 number and configured per operator policy:
- the S‑CSCF attempts translation of the E.164 address in the SIP URI to a globally routable SIP URI using the procedures specified in clause 4.3.5. As stated in clause 4.3.5, if the E.164 address translation fails, the request may be forwarded to a BGCF to allow routing to the PSTN and if the translation succeeds, the Request URI is updated and the request is routed based on the SIP URI that was obtained.
NOTE 5: When requests are sent towards another domain they may, if required, be routed via a local network exit point (IBCF), which will then forward the request to the entry point of the other domain. More details on this can be found in clause 4.14 and Annex I.
Based on local configuration, the S‑CSCF may be provisioned as the contact point within an operator's network for transit IMS scenarios and may perform transit routing functions (see clause 5.19).
Charging and resource utilisation:
- Generation of CDRs
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4.6.4 Breakout Gateway Control Function
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Based on local configuration, the Breakout Gateway Control Function (BGCF) may be provisioned as the contact point within an operator's network for transit IMS scenarios as described in clause 5.19. Otherwise the BGCF processes requests for routing from an S‑CSCF for the case were the S‑CSCF has determined that the session cannot be routed using DNS or ENUM/DNS (see clauses 5.4.3, 5.19 and 4.3.5 for more information).
The BGCF determines the next hop for routing the SIP message. This determination may be based on information received in the protocol, administrative information and/or database access. For PSTN terminations, the BGCF determines the network in which PSTN/CS Domain breakout is to occur. If the routing determination is such that the breakout is to occur in the same network in which the BGCF is located, then the BGCF shall select a MGCF that will be responsible for the interworking with the PSTN/CS Domain. If the routing determination results in break out in another network, the BGCF will forward this session signalling to another BGCF in the selected network. If the routing determination results in the session being destined for another IMS network, the BGCF forwards the message to an I‑CSCF in this IMS network. If the BGCF determines that there is another IP destination for the next hop, it forwards the message to that contact point.
There may be multiple BGCFs within an operator's network. The functions performed by the BGCF are:
- Determines the next hop for SIP routing.
- For PSTN terminations, select the network in which the interworking with the PSTN/CS Domain is to occur. If the interworking is in another network, then the BGCF will forward the SIP signalling to the BGCF of that network.
- For PSTN terminations, select the MGCF in the network in which the interworking with PSTN/CS Domain is to occur and forward the SIP signalling to that MGCF. This may not apply if the interworking is a different network.
- Generation of CDRs
NOTE: When requests are sent towards another domain they may, if required, be routed via a local network exit point (IBCF), which will then forward the request to the entry point of the other domain. More details on this can be found in clause 4.14 and Annex I.
The BGCF may make use of information received from other protocols, or may make use of administrative information, when making the choice of which network the interworking shall occur.
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4.6.5 Void
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4.7 Multimedia Resource Function
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The architecture concerning the Multimedia Resource Function is presented in Figure 4.7 below.
Figure 4.7: Architecture of MRF
The MRF is split into Multimedia Resource Function Controller (MRFC) and Multimedia Resource Function Processor (MRFP).
Tasks of the MRFC are the following:
- Control the media stream resources in the MRFP.
- Interpret information coming from an AS and S‑CSCF (e.g. session identifier) and control MRFP accordingly.
- Generate of CDRs.
Tasks of the MRFP include the following:
- Control of the bearer on the Mb reference point.
- Provide resources to be controlled by the MRFC.
- Mixing of incoming media streams (e.g. for multiple parties).
- Media stream source (for multimedia announcements).
- Media stream processing (e.g. audio transcoding, media analysis).
- Floor Control (i.e. manage access rights to shared resources in a conferencing environment).
Tasks of an Application Server with regards to MRF are e.g. the following:
- Conference booking and management of booking information (e.g. start time, duration, list of participants)
The protocol used for the Mr and Mr′ reference points is SIP (as defined by IETF RFC 3261 [12], other relevant IETF RFCs and additional enhancements introduced to support 3GPP´s needs).
The Cr reference point allows interaction between an Application Server and an MRFC for media control. Further information on the Cr reference point is provided in TS 23.218 [71].
The Mp reference point allows an MRFC to control media stream resources provided by an MRFP.
The Mp reference point has the following properties:
- Full compliance with the H.248 standard.
- Open architecture where extensions (packages) definition work on the interface may be carried out.
The protocol for the Mp reference point is described in TS 29.333 [59].
4.7a Media Resource Broker
The MRB supports the sharing of a pool of heterogeneous MRF resources by multiple heterogeneous applications. The MRB assigns (and later releases) specific suitable MRF resources to calls as requested by the consuming applications, based on MRF attributes specified by the applications as well as other criteria. For more information see TS 23.218 [71].
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4.8 Security Concepts
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IM CN Subsystem functional elements provide security, as needed, by security methods defined in TS 33.203 [19] and TS 33.210 [20]. If interacting with external Networks, Security Associations are provided in accordance with operator policy.
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4.9 Charging Concepts
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IM CN subsystem functional elements provide support for offline and online charging. This includes support for charging correlation, e.g. between IM CN subsystem and PS domain. The charging architecture, charging principles and charging data for IM CN subsystem are described in TS 32.240 [25] and TS 32.260 [26]. The charging correlation information between IM CN subsystem and PS domain are also described in TS 24.229 [10a] and TS 29.207 [11a].
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4.10 IMS group management concepts
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4.10.0 General
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This clause describes architectural concepts to fulfil the requirements for IMS Group Management described in TS 22.250 [32].
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4.10.1 IMS group administration
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The capabilities required for IMS group management are defined in clause 5.4 of TS 22.250 [32]. The Ut reference point is used to manage groups from the UE. This does not preclude the use of other mechanisms for group management, e.g. using OSA or OA&M mechanisms; the details of these other mechanisms are out of scope of this document.
The Ut reference point shall support a scenario where one single Application Server is used to create groups that can be utilized for different services, possibly hosted by different ASs.
NOTE: Such an Application Server is sometimes referred to as a Group and List Management Server (GLMS).
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4.10.2 Group identifiers
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Each group shall be addressable by a globally unique group identifier. The group identifier shall take the form of a Public Service Identifier.
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4.11 Relationship to 3GPP Generic User Profile (GUP)
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It shall be possible to apply the mechanisms and format of the 3GPP Generic User Profile (GUP) to IM CN Subsystem user related data. The 3GPP Generic User Profile (GUP) is described in TS 23.240 [31].
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4.12 Network Address Translation traversal in access network
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It shall be possible to support the scenario where a NAT(-PT)/NAPT(-PT) residing between the IMS functionality in the UE and the P‑CSCF has to be traversed for IMS communication. This shall include at least the types of NATs that implement address and port dependent mapping together with address and port dependent filtering, RFC 4787 [51].
NOTE: The UE may be one piece of equipment, or it may be a network of elements located on a end-user's physical premises.
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4.13 Identification of IMS communication Services
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4.13.1 General
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This clause describes the architectural requirements for the identification of IMS communication services.
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4.13.2 Identification of IMS communication Services
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An IMS Communication Service Identifier (ICSI) provides a framework for the identification of IMS communication services utilising the IMS enablers. An IMS communication service is provided via the use of the IMS enablers. At terminals, the use of a communication service identifier is similar to the use of the port concept in TCP/IP, in that it allows applications in a terminal and the network that use SIP for communication purposes to be identified. In the terminal this means dispatching a SIP message to the correct application and in the network it means selection of the correct application server over ISC. Examples of IMS based applications and communication services are OMA messaging and OMA PoC.
An IMS communication service defines restrictions to which SIP procedures are possible within a single SIP session or standalone transaction and how those SIP procedures are used. The IMS communication service contains an aggregation of zero, one, or several media components and the service logic managing the aggregation, represented in the protocols used. Its behaviour and characteristics may be standardized as done for the two examples above, or proprietary and specific for e.g. an operator or an enterprise.
A service description specifies this behaviour and states e.g. the allowed media combinations and state transitions as a consequence of signalling and use of IMS enablers in the network and terminals.
NOTE 1: The application server(s) required to support the IMS communication service are required to be included in the path of the standalone transaction or SIP session at the establishment of the SIP dialogue and therefore can not be linked in after the initial SIP request, i.e. once a SIP session has been established, it is not possible to change the IMS communication service for that session. A UE can establish a new SIP session with another IMS communication service identifier if it is required to add a media that is not supported by the existing IMS communication service.
The need of applying a service identifier is to be taken within the specification of each individual service.
The communication service identifier identifies IMS communication services and shall be included in the relevant SIP methods.
The IMS communication service identifier shall fulfil the following requirements:
1. It shall be possible for the UE and an Application Server (AS) to set the IMS communication service identifier in a SIP request, e.g. in the REGISTER and INVITE request.
2. Based on operator policy the S‑CSCF or an AS shall be able to validate an IMS communication service identifier in a SIP request. This includes e.g. to check the syntactical correctness of a service identifier and policing the usage of a communication service identifier. It shall also be possible for the S‑CSCF and an AS to indicate that the value of the IMS communication service is validated. An asserted IMS communication service identifier shall be able to be indicated by the service in SIP responses to the SIP request along with information that the IMS communication service identifier is asserted.
NOTE 2: If the asserted IMS communication service provided in the SIP response differs from the requested IMS communication service, the UE can make a local decision on whether it wish to continue the session. The UE will ignore any IMS communication service it does not support. User interaction is not needed.
NOTE 3: If the asserted IMS communication service provided in the SIP response differs from the requested IMS communication service, the VPLMN can make a local decision on whether it wish to continue the session. If continuing, the asserted IMS communication service is used in VPLMN for the remainder of the session (e.g. to provide service aware charging).
3. It shall be possible, e.g. for the UE, S‑CSCF and AS, to identify an IMS service uniquely by the IMS communication service identifier.
4. It shall be possible for the S‑CSCF to invoke appropriate service logic based on the IMS communication service identifier contained in a SIP request, e.g. route a SIP request containing a service identifier based on initial filter criteria to the correct AS.
5. It shall be possible for the UE to invoke appropriate application based on the IMS communication service identifier contained in a received SIP request.
6. It shall be possible for the UE to indicate its service capabilities to the network, e.g. during registration, using the IMS communication service identifier.
NOTE 4: The UE does not need to indicate all the service capabilities it supports to the network.
7. It shall be possible for the network to inform the UE about service capabilities, represented by ICSIs, of the network.
8. The structure of the IMS communication service identifier shall be as simple as possible, i.e. the IMS communication service identifier shall be limited to identify a service.
9. Based on operator policy S‑CSCF and AS shall consider the IMS communication service identifier for online and offline charging, e.g. put appropriate data into call detailed records.
10. The communication service identifier shall be capable of being an input into the policy control and charging rules.
11. It shall be possible to use the IMS communication service identifier as a means to authorize whether a subscriber is allowed to initiate or receive request for a communication service.
12. The communication service identifier shall be taken into account when selecting the correct UE(s), if multiple UEs are registered for the same Public User Identity(s).
13. The usage of communication service identifiers shall not adversely affect interoperability between IMS networks and interoperability with external SIP networks and CS networks. The behaviour of a network receiving the IMS requests without an IMS communication service identifier is a matter of operator policy. Usage of communication service identifiers shall not decrease the level of interoperability with networks and UEs that are unaware of the communication service identifier.
14. It shall be possible for the IMS network and UE to support communications that do not use a communication service identifier. In the case that an IMS communication service identifier is not present then the network may assume a particular IMS communication service.
15. The usage of communication service identifiers shall not restrict the inherent capabilities of SIP.
16. The usage of communication service identifiers shall not require additional user interaction, i.e. the communication service identifier is assumed to be "added" by the UE that initiates the communication.
17. Where a communication service needs to be identified, one requested IMS communication service identifier shall be included by the originator of the session in the SIP method that initiates a SIP dialogue or standalone transaction. In addition to the requested IMS communication service, the supported IMS communication services may be included.
18. This version of the specification does not require the capability to use multiple requested IMS communication service identifiers in the SIP method that initiates a SIP dialogue or standalone transaction. However, the protocol implementation shall nonetheless be prepared to transport more than one requested IMS communication service identifier and the network shall be prepared to handle the situation if multiple IMS communication service identifiers are received but the network is only required to take action on one of the values. The same applies for the UE.
19. To facilitate service aware charging for roaming, it shall be possible to provide an asserted IMS communication identifier service to the VPLMN.
The network and the terminal shall be able to continue operation as defined in 3GPP Release 5 and 3GPP Release 6.
The communication service identifier shall be available at least in the following interfaces:
- ISC, Gm, Ma, Mi, Mj, Mk, Mw, Mg, Mr, Mr′;
- Cx; Dx (e.g. as part of the iFC);
- Rx, N5;
- Rf, Ro.
NOTE 5: The communication service identifier does not replace the public service identity (PSI). The communication service identifier would be used to indicate the communication service used to access the service addressed via a PSI and is required to identify the communication service even when SIP requests are sent towards another entity without using a PSI.
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4.13.3 Identification of IMS applications
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An IMS application is an application that uses an IMS communication service(s) in order to provide a specific service to the end-user. The IMS application uses specific IMS Communication Service(s) and provides the end user service through the reuse of the SIP communication part of service. The IMS application does not extend the definition of the IMS communication service. The IMS application reference identifies the application utilising the IMS communication service.
Figure 4.13-1: IMS applications on top of an IMS communication service
The IMS application reference is used to identify the IMS applications other than the default for the IMS communication service. The IMS application reference has significance at the UE and the SIP AS behaving as SIP endpoints. The means to transport the IMS application reference is defined within the IMS communication services. When used, it shall be possible to transport the IMS application reference on at least on the following interfaces:
- ISC, Gm, Ma; Mi, Mj, Mk, Mw, Mg, Mr, Mr′, Rx, N5, Rf, Ro.
It shall be possible to register the IMS application reference. The IMS application reference can be taken into account when selecting the correct UE(s), if multiple UEs are registered for the same Public User Identity(s).
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4.14 Border Control concepts
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Based on operator preference, border control functions may be applied between two IM CN subsystem networks or between an IM CN subsystem network and other SIP based multimedia network. These functions are provided by the IBCF and include:
- Controlling transport plane functions;
- Supporting functions to allow establishing communication between disparate address realms' SIP applications;
- Supporting functions to allow establishing communication between IM CN subsystems using different media codecs based on the interworking agreement and session information;
- Providing network configuration hiding to restrict the following information from being passed outside of an operator's network: exact number of S‑CSCFs, capabilities of S‑CSCFs, or capacity of the network, etc;
NOTE 1: Network configuration hiding was not intended to be invoked in IMS roaming scenarios when the P‑CSCF and IBCF are both located in the visited network as information available in certain SIP headers may be used by the home network for further processing of signalling messages.
- Screening SIP signalling information based on source/destination and operator policy (e.g. remove information that is of local significance to an operator) and optionally, for an IBCF located in the home network, policing the IMS Communication Service ID;
- Generation of CDRs;
- Invoking an IWF when interworking between different SIP profiles or different protocols (e.g. SIP and H.323) is necessary; in this case the IWF acts as an entry point for the IMS network;
NOTE 2: IWF and IBCF may be co-located. The IWF is not specified within this release of the specification.
- Selecting the appropriate signalling interconnect.
- Indicating whether an incoming SIP request is to be handled as an originating request by subsequent nodes in the IMS network.
- For an originating session leaving an IBCF, the IBCF of the originating network, if configured through operator policies, invokes an AS for the signing of attestation and identity information, if available in the incoming request. The IBCF includes the signed information in the outgoing request.
- For an originating session leaving an IBCF, the IBCF of the originating network, if configured through operator policies, invokes an AS for the signing of RCD information or RCD URL, if available in the incoming request. The IBCF includes the signed information in the outgoing request as per Annex AF.
- For an originating session leaving an IBCF, the IBCF of the originating network, if configured through operator policies, invokes an AS for the signing of Resource-Priority related information, if available in the incoming request. The IBCF includes the signed Resource-Priority related information in the outgoing request.
- For a terminating session entering the IBCF without identity attestation information, the IBCF adds, if configured through policies, gateway attestation information based on the network from which the request was received.
- For a terminating session entering the IBCF with signed identity attestation information, the IBCF, if configured through policies, invokes an AS for signature verification.
- For a terminating session entering the IBCF with signed RCD information or signed RCD URL, the IBCF, if configured through policies, invokes an AS for signature verification as per Annex AF.
- For a terminating session entering the IBCF with signed Resource-Priority information, the IBCF, if configured through policies, invokes an AS for signature verification.
If border control concepts are to be applied in an IMS network, the IBCF acts as an entry point for this network (instead of the I‑CSCF) and also acts as an exit point for this network.
NOTE 3: In this case the IBCF and I‑CSCF may be co-located as a single physical node.
Based on local configuration, the IBCF may perform transit routing functions (see clause 5.19).
More detailed description of these functions is provided in Annex I.
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4.15 IMS in transit network scenarios
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4.15.1 General concepts
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IMS generally provides services to end user customers of a network operator by directly supporting multimedia communications services to or from that operator's customers. However IMS may also be used in a number of other configurations where the capabilities of IMS are used to support CS domain customers of an IMS operator or in various other kinds of business arrangements where the capabilities may be used to support interconnection of other networks.
Clause 4.15.2 describes several types of configurations in which IMS might be used to support such network interconnection. These are not intended to represent all possible applications of IMS, but rather provide some basis for the mechanisms by which IMS provides these transit functionalities. Further description of IMS transit network procedures are found in Clauses 5.4a.2 and 5.19.
Clause 4.15.3 describes the cases in which IMS application services can be provided in relation to the IMS transit traffic.
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4.15.2 IMS transit network configurations
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There are at least three general cases in which IMS may be used for transit network support. These could be classified as in the following:
a) IMS operator providing transit functionality for its own, non-IMS (CS domain), customers:
In this case the operator is serving its own customers, some of which have been migrated to IMS while others are still CS Domain subscribers. In this case SIP traffic arrives at a configured entry point and PSTN traffic arrives at the operator's MGCF. This is similar to the normal Mobile Terminating cases for IMS, but in this case the CS domain subscribers do not have an IMS subscription. For the case where the destination user is not an IMS subscriber, the operator needs to route the session to the CS domain.
b) IMS operator providing transit functionality to enterprise networks:
In this case the operator is serving as a transit network for an enterprise IP network and provides connectivity to both PSTN and IP endpoints. Traffic from the enterprise network arrives at a provisioned routing entity and needs to be routed to either an IP network or to the PSTN depending on the terminating endpoint.
c) IMS operator providing transit functionality to other network operators:
In this case the operator is serving as an IMS session based routing backbone for a PSTN operator or another IP network and provides connectivity to both PSTN and IP endpoints (PSTN <‑> PSTN, IP <‑> IP, PSTN <‑> IP). Traffic from the PSTN operator arrives at configured MGCFs for translation to SIP. IMS traffic arrives at a configured entry point. In either case the operator needs to route the traffic to either an IP network or to the PSTN depending on the terminating endpoint.
An IMS operator can provide transit functionality as above in addition to (originating or terminating) IMS services. In these situations analysis of an incoming SIP request is required before it can be determined whether transit or terminating services need to be provided for this request.
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4.15.3 Providing IMS application services in transit network scenarios
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When IMS provides transit functionality to other network operators or enterprise networks, the IMS may also provide IMS applications services to the network operator or enterprise network.
Figure 4.15.3-1: IMS application services reference point for transit network scenarios
The Transit service invocation shall be performed based on local configured Transit invocation criteria that are provided for the specific transit scenario.
The Transit invocation criteria for invocation shall have the possibility to take into account,
- (served) preceding network,
- (served) succeeding network and
- other additional session information.
NOTE: The Transit invocation criteria are intended to be per served interconnected network basis and not per subscriber basis.
Similar to the initial filter criteria for a user profile, the Transit invocation criteria may have service point triggers based on different information in the request, such as source/destination, SIP method, session case, SIP header and SIP body. The service invocation procedure shall support suppression/avoidance of conflicting services, multiple invocations of the same service and loopback scenarios.
The IMS application services provided can be classified as:
a) Originating IMS application services:
In this case the IMS operator provides IMS application services for SIP traffic being received from the served network operator or enterprise network. The application services, appropriate for the received SIP traffic, will be invoked when received from the served network, after which the traffic is routed towards the destination endpoint.
b) Terminating IMS application services:
In this case the IMS operator provides IMS application services for SIP traffic destined to a served network operator or enterprise network. The application services, appropriate for the received SIP traffic, will be invoked when the served network has been identified as the next network, or when the traffic has been identified as destined to the served network.
4.15a Roaming Architecture for Voice over IMS with Local Breakout
The Transit and Roaming Function is the combined functionalities of the transit network functions as defined in clause 4.15 and the roaming specific functions defined in this clause.
The following architectural requirements apply:
- The P-CSCF, S-CSCF, the Transit and Roaming Function and other nodes performing routing procedures in different networks may control the application of OMR procedures by indicating in the signalling whether an IBCF/TrGW should not apply OMR.
- In order to allow scenarios where the media is not routed through the originating HPLMN, IBCFs handling incoming requests to the network should support OMR and allow bypass of TrGWs. Anchoring of media may be controlled via outgoing IBCFs.
- The HPLMN shall decide whether to perform the loopback procedure based on local policy and on knowledge of the support of the procedure in the VPLMN.
- The VPLMN shall be provided by the HPLMN with enough information to determine whether home routing has been applied (or has not been applied):
- The HPLMN shall send an indication to the VPLMN that this session set-up is a loopback to allow differentiation from any other incoming call. By this means the VPLMN is able to apply the correct treatment for this looped incoming leg incl. charging and routing decisions.
- If local policy requires access to BGCF routing data to make the loopback decision for a particular originating INVITE request, then the loopback decision should be performed in the BGCF. Else it should be performed in the S‑CSCF.
- The Transit and Roaming Function shall perform call routing towards the terminating network by selecting appropriate egress point (e.g. MGCF for CS/PSTN, IBCF to other IMS networks, or I-CSCF for termination in own network). The Transit and Roaming Function may use information such as originating UE location information to select a nearby egress point for media anchoring.
- The VPLMN may provide the HPLMN with a reference to the preferred Transit and Roaming Function to steer the selection of the Transit and Roaming Function. If the VPLMN does not provide the Transit and Roaming Function address then the HPLMN shall use the default derived address for the VPLMN.
- When the HPLMN operator does not use loopback to the Transit and Roaming Function in VPLMN, the HPLMN shall be able to anchor the media. This ensures that the signalling and media are routed together.
An overview of the principles and flows of the Roaming Architecture for Voice over IMS with Local Breakout are depicted in Annex M, clause M.3.
4.15b Roaming Architecture for Voice over IMS with home routed traffic
In this scenario, the anchor point for the IP address for both the IMS signalling and media traffic is in the home network for a roaming UE, i.e. for 3GPP systems, the GGSN, PGW or UPF for a roaming UE is in the HPLMN of the UE.
The following architecture requirements apply:
- The P-CSCF is located in the HPLMN
Additional architecture requirements and functions that are needed to support IMS services with home routed traffic are depicted in Annex W for EPS and in Annex Y for 5GS.
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4adbe58b357307ea5b45584ce0f667fa
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23.228
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4.16 Support of multimedia telephony
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4adbe58b357307ea5b45584ce0f667fa
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23.228
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4.16.1 Telephony Application Server
|
The Telephony Application Server is a SIP AS providing the network support for the multimedia telephony service, TS 22.173 [53]. If specific procedures and message flows include or require media interaction, the TAS and MRFC may be collocated.
NOTE: The support of multimedia telephony services may be allocated to one or more Application Servers.
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4adbe58b357307ea5b45584ce0f667fa
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23.228
|
4.16.2 Identification of multimedia telephony
|
The multimedia telephony communication service shall be associated with a communication service identifier to allow easy identification of the service.
When multimedia telephony is supported in a network, Voice/video calls originating from the PSTN/CS domain shall be marked with the communication service identifier associated with multimedia telephony communication service.
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4adbe58b357307ea5b45584ce0f667fa
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23.228
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4.16.3 Session setup principles
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When establishment of UE initiated IP‑CAN bearer(s) for the media is required it is recommended to reserve IP‑CAN bearer(s) at the reception of the SDP answer. If the UE has been made aware of the operator policies with regards to allowed media for the multimedia telephony service, then the UE may reserve IP‑CAN bearer(s) at the sending of the SIP INVITE request. For multimedia telephony, the UE should only mark resource reservation as required for voice and video.
When there are no requirements for resource reservation or when required resources are available on the originating side, the P‑CSCF on the terminating side may send available session information to the PCRF/PCF at the reception of the SDP offer, as in such cases the UE can attempt resource reservation before sending the SDP answer.
If configured through policies, the telephony AS, or any other AS, may perform for originating requests attestation of the identity of the originating subscriber.
If configured through policies, the telephony AS, or any other AS, may perform for originating requests attestation of the RCD information or RCD URL of the originating subscriber as per Annex AF.
If configured through policies, the telephony AS, or any other AS, may perform for originating IMS priority sessions, assertion of authorization for the Resource-Priority information.
If configured through operator policies, the telephony AS may perform for diverted sessions attestation of the identity of the diverting subscriber initiating the diversion,
In addition and if configured through policies, the telephony AS, or any other AS, may perform for terminating requests signature verifications, if one or more signatures is included.
In addition and if configured through policies, the telephony AS, or any other AS, may perform signature verification of the RCD information or RCD URL of the originating subscriber for terminating requests, if a signature is included as per Annex AF.
NOTE: Only one network element performs attestation for an originating subscriber in the originating network.
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4adbe58b357307ea5b45584ce0f667fa
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23.228
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4.17 Support of short message service
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4adbe58b357307ea5b45584ce0f667fa
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23.228
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4.17.1 IP Short Message Gateway (IP-SM‑GW)
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The IP‑SM‑GW acts as an SIP-AS in the IMS domain to provide the protocol interworking for the delivery of the short message between the UE and the Service Centre. All functionalities and interfaces of IP‑SM‑GW are defined in TS 23.204 [56].
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4adbe58b357307ea5b45584ce0f667fa
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23.228
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4.18 Support of Number portability
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4adbe58b357307ea5b45584ce0f667fa
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23.228
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4.18.1 Number portability
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Number portability (NP) allows a user to retain their E.164 number when changing subscriptions from one network operator to another. As such, NP applies to TEL URIs and SIP URIs representing E.164 addresses. NP is subject to regional requirements and is accomplished through the retrieval of ported data from those databases. The specification of these databases is out of the scope of this document, but the NP data may be accessed through ENUM/DNS or accessed via existing (PSTN‑ and CS‑domain) NP databases using the legacy PSTN/CS-domain protocols, such as TCAP.
Support of NP within a network and the exact means to make the number portability data available to IMS, is subject to and configured per operator policy. NP is not mandated by this specification on any network operator.
As configured per operator policy, IMS ENUM interfaces can be updated to support handling of the PSTN ENUM service per IETF RFC 4769 [57], which provides a URI containing an E.164 number with NP routing information and NP dip indicators. The IMS entity receiving NP information as a result of an ENUM/DNS query (e.g. S‑CSCF), needs to support NP protocol parameters retrieved as part of ENUM/DNS procedures contained in clause 4.3.5. This IMS entity and any subsequent IMS entities/network elements used to process the call to the PSTN shall not remove the NP protocol parameters inserted in SIP messaging as part of the NP data retrieval procedure.
NP data can also be made available by means of direct access to PSTN/CS‑domain NP Databases using the legacy PSTN/CS-Domain interfaces and protocols. To support this existing interface within the network, the requesting and subsequent network elements need to support, or not remove, NP protocol parameters within SIP messages that result from the NP data retrieval procedures. The procedures to retrieve the NP data using the legacy PSTN/CS‑domain interfaces are out of scope of this specification.
Alternatively, per operator policy, the BGCF can retrieve NP data as part of the procedures to select an MGCF for PSTN connection. The interface used at the BGCF to retrieve the NP data is out of scope of this specification.
When clause 4.15a (Roaming Architecture for Voice over IMS with Local Breakout) is in use and the Home Network decides to loop-back the call to the visited network, the Home network can choose not to retrieve NP data and leave it to the visited network.
Alternatively, per operator policy, the MGCF may support legacy interfaces to retrieve number portability data.
NOTE: Although legacy protocols are used to access the number portability database, this does not imply that the IMS nodes (CSCFs, BGCFs) need to implement such protocols.
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4adbe58b357307ea5b45584ce0f667fa
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23.228
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4.19 Support of Preferred Circuit Carrier Access and Per Call Circuit Carrier Selection
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4adbe58b357307ea5b45584ce0f667fa
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23.228
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4.19.1 Preferred Circuit Carrier Access and Per Call Circuit Carrier Selection
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Preferred Circuit Carrier Access allows the network operator to configure a preferred long distance circuit carrier for a subscriber, set of subscribers or all subscribers on the network. All long distance calls from a subscriber are routed to the long distance circuit carrier when preferred circuit carrier access applies. A SIP message parameter indicates the preferred circuit carrier selected. This parameter can be delivered to the PSTN. An application server can be used to insert preferred circuit carrier parameters. The BGCF needs to consider and can insert, the preferred circuit carrier parameters when routing calls towards an MGCF.
Preferred Circuit Carrier Selection per call, also known as Dial-around, allows the subscriber to request a long distance carrier for a specific call. A dial-around request is dialled by the subscriber along with the called party number at call origination. As configured per operator policy, the dial-around circuit carrier selection can take precedence over other preferred circuit carrier selection that can be configured in the network. Therefore, based on operator policy, the preferred circuit carrier parameter is not to be replaced if already present in a SIP message with a dial-around indicator. A SIP message parameter indicates the preferred circuit carrier selected with a dial-around indicator. This parameter is delivered to the PSTN.
Support of preferred circuit carrier access and dial-around is optional within a network and is subject to and configured per, operator policy.
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4adbe58b357307ea5b45584ce0f667fa
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23.228
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4.20 Support of IMS Service Centralization and Continuity
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IMS Service Centralization, defined in TS 23.292 [66] provides communication services such that all services and service control, are based on IMS mechanisms and enablers. It enables IMS services when using CS access as bearer for the media.
IMS Service Continuity, defined in TS 23.237 [67] provides Session Transfer mechanisms to maintain service continuity in the event of access transfer for the case when such events are not hidden from the IMS session layer and thus service continuity could not otherwise be maintained.
All functionalities and reference points are defined in TS 23.292 [66] and TS 23.237 [67].
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4adbe58b357307ea5b45584ce0f667fa
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23.228
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4.21 Support of Overlap Signalling
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The support of overlap signalling consists of the functionality for conversion between overlap and en-bloc, as well as the functionality for digit collection.
The above mentioned functionalities may be implemented in different network nodes depending on the operator's deployment strategy (e.g. AS, IBCF, MGCF).
NOTE 1: Support for overlap signalling in the IMS is an option limited to the interworking function located within the PSTN/ISDN networks that use overlap signalling.
NOTE 2: Digit collection limits the number of messages with incomplete number and to find another node that support overlap signalling.
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