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Content for  TS 23.434  Word version:  18.1.0

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6.4  Functional entities descriptionp. 25

6.4.1  Generalp. 25

Each subclause is a description of a functional entity corresponding to SEAL and does not imply a physical entity.

6.4.2  Application planep. 25

6.4.2.1  Generalp. 25

Entities within the application plane of a VAL system provide application control and media specific functions to support one or more VAL services.

6.4.2.2  VAL clientp. 25

The VAL client provides the client side functionalities corresponding to the vertical applications (e.g. V2X client). The VAL client supports interactions with the SEAL client(s).

6.4.2.3  VAL serverp. 25

The VAL server provides the server side functionalities corresponding to the vertical applications (e.g. V2X application servers). The VAL server acts as CAPIF's API invoker as specified in TS 23.222.

6.4.2.4  SEAL clientp. 26

The SEAL client provides the client side functionalities corresponding to the specific SEAL service. The SEAL client(s) supports interactions with the VAL client(s). The SEAL client also supports interactions with the corresponding SEAL client between the two UEs.

6.4.2.5  SEAL serverp. 26

The SEAL server provides the server side functionalities corresponding to the specific SEAL service. The SEAL server supports interactions with the VAL server(s). The SEAL server acts as CAPIF's API exposing function as specified in TS 23.222. The SEAL server also supports interactions with the corresponding SEAL server in distributed SEAL deployments.

6.4.2.6  VAL user databasep. 26

This functional entity contains information of the user profile associated with a VAL service that is served by the VAL service provider at the application plane.
Each VAL service may have a corresponding user database e.g. MCPTT user database as defined in TS 23.379, MCVideo user database as defined in TS 23.281 and MCData user database as defined in TS 23.282.
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6.4.3  Signalling control planep. 26

6.4.3.1  SIP entitiesp. 26

6.4.3.1.1  Signalling user agentp. 26
This functional entity acts as the SIP user agent (both client and server) for all SIP transactions.
6.4.3.1.2  SIP ASp. 26
The SIP AS functional entity supports the following functions on behalf of the VAL service:
  • influencing and impacting the SIP session; and
  • supporting event subscription and event notification.
6.4.3.1.3  SIP corep. 26
6.4.3.1.3.1  Generalp. 26
The SIP core contains a number of sub-entities responsible for registration, service selection and routing in the signalling control plane.
The SIP core shall be either:
  1. compliant with TS 23.228, i.e. the SIP core is a 3GPP IP multimedia core network subsystem; or
  2. a SIP core, which internally need not comply with the architecture of TS 23.228, but with the reference points that are defined in subclause 6.5.3 (if exposed), compliant to the reference points defined in TS 23.002.
The data related to the functions of the SIP core, e.g. for data for application service selection, the identity of the serving registrar or authentication related information may be provided by the PLMN operator responsible for the bearer plane. In this case, the SIP database that is the source of the data may be part of the HSS. Alternatively, this data may be provided by the VAL service provider. In this case, the source of the data may be the VAL service provider's SIP database.
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6.4.3.1.3.2  Local inbound / outbound proxyp. 27
The local inbound / outbound proxy functional entity acts as both an inbound proxy and an outbound proxy for all SIP transactions. This functional entity can provide the following functions:
  • NAT traversal;
  • Resource control;
  • Route/forward requests and responses to the user agents;
  • SIP signalling security; and
  • Depending on the PLMN operator policy, discovery and address resolution, including E.164 numbers.
6.4.3.1.3.3  Registrar finderp. 27
The registrar finder functional entity is responsible for:
  1. Identifying the serving registrar / application service selection functional entity. The serving registrar / application service selection functional entity is identified using information provided either by the PLMN operator's own SIP database or the VAL service provider's SIP database, and optionally using the PLMN operator's internal information e.g. network topology, registrar availability.
    1. Registrar finder and registrar in the VAL service provider domain: registrar finder in the VAL service provider's domain uses the information from the VAL service provider's SIP database to identify the serving registrar in the VAL service provider domain.
    2. Registrar finder and registrar in the PLMN operator domain: registrar finder uses information from PLMN operator's SIP database to identify the serving registrar in the PLMN operator domain.
    3. Registrar finder in PLMN operator domain and registrar in VAL service provider domain: registrar finder uses information from the VAL service provider's SIP database to identify the serving registrar in the VAL service provider domain.
  2. Providing discovery and address resolution, including E.164 numbers.
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6.4.3.1.3.4  Registrar / application service selectionp. 27
The registrar / application service selection functional entity provides the following functions:
  • Registrar function (with integral provision of a location server) and also acts as an inbound proxy (with access to the integral location server), and outbound proxy for all SIP transactions where application service selection is required. It registers the user and maintains the association of the location and identity of the user in a location service. It provides notifications of the registration states.
  • Supports authentication for identities provided within SIP signalling. Both the registrar (with integral location server) and authentication functions are supported by access either to the public network's own SIP database or the VAL service provider's SIP database.
  • Can provide the application service selection for all SIP transactions, possibly based on application service selection information stored by either the public network's own SIP database or the VAL service provider's SIP database.
  • Performs SIP signalling security.
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6.4.3.1.4  Diameter proxyp. 28
This functional entity acts as a proxy agent for Diameter messaging as specified in RFC 6733.
The Diameter proxy, when used on the AAA-2 interface, is collocated with the migration management server.
Other instances of the Diameter proxy may also be present in the SIP core / IMS.

6.4.3.2  SIP databasep. 28

6.4.3.2.1  Generalp. 28
The SIP database contains information concerning the SIP subscriptions and corresponding identity and authentication information required by the SIP core, and such information as application service selection.
In deployment scenarios where the PLMN operator provides the SIP core, this database is provided by the HSS.
In deployment scenarios where the VAL service provider provides the SIP core, the SIP database may be provided by the VAL service provider.
Access to the data residing in the SIP database is restricted to the SIP core entities that are specifically serving the subscriber/user whose data are stored, i.e. registrars and registrar finders can access SIP databases only when they are part of the same trust domain for the data being provided.
The SIP database is responsible for storing the following user related information:
  • signalling plane user identities: Numbering and addressing information;
  • signalling plane security information: SIP core access control information for authentication and authorization;
  • VAL UE Location information at inter-system level: the SIP database supports the user registration, and stores inter-system location information, etc.; and
  • signalling plane subscription profile (including initial filter criteria).
The SIP database also generates signalling plane security information for mutual authentication, communication integrity check and ciphering.
Based on this information, the SIP database is also responsible to support the call control and session management entities of the SIP core.
The SIP database consists of the following functionalities:
  • support for control functions of the SIP core such as the Registrar and Registrar finder. This is needed to enable subscriber usage of the SIP core services. This functionality is independent of the access network used to access the SIP core; and
  • authentication functionality required by the SIP core to authenticate the VAL UE.
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6.4.3.2.2  SIP database logical functionsp. 29
The SIP database provides the following logical functions:
  1. mobility management;
    • provides the UE mobility through the SIP core.
  2. registrar assignment support;
    • provides to the registrar finder the required capabilities for VAL services based on VAL service provider requirements on a per-user basis, (e.g. whether a particular registrar within the PLMN operator's network (e.g. a registrar reserved for VAL service use or a registrar in a secure location) or a registrar within the VAL service provider network is assigned.
  3. call and/or session establishment support;
    • provides the call and/or session establishment procedures in the SIP core. For terminating traffic, it provides information on which registrar currently hosts the user.
  4. user security information generation;
    • provides generation of user authentication, integrity and ciphering data for the SIP core.
  5. signalling plane security support;
    • provides authentication procedures to access VAL services by storing the generated data for authentication, integrity and ciphering at the signalling plane and by providing these data to the appropriate registrar.
  6. user identification handling;
    • provides the appropriate relations among all the identifiers uniquely determining the signalling plane identities in the SIP core e.g. IMS public identities.
  7. access authorisation; and
    • provides authorisation of the user for mobile access when requested by the registrar e.g. by checking that the user is allowed to roam to that visited network.
  8. service authorisation support.
    • provides basic authorisation for terminating call/session establishment and service invocation. The SIP database may update the registrar with filter criteria to trigger the VAL server(s).
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6.4.3.3  HTTP entitiesp. 29

6.4.3.3.1  HTTP clientp. 29
This functional entity acts as the client for all hypertext transactions.
6.4.3.3.2  HTTP proxyp. 29
This functional entity acts as a proxy for hypertext transactions between the HTTP client and one or more HTTP servers. The HTTP proxy terminates a TLS session on HTTP-1 with the HTTP client of the VAL UE allowing the HTTP client to establish a single TLS session for hypertext transactions with multiple HTTP servers that are reachable by the HTTP proxy.
The HTTP proxy terminates the HTTP-3 reference point that lies between different HTTP proxies. It may provide a topology hiding function from HTTP entities outside the trust domain of the VAL system.
The HTTP proxy shall be in the same trust domain as the HTTP clients and HTTP servers that are located within a VAL service provider's network. There can be multiple instances of an HTTP proxy e.g. one per trust domain.
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6.4.3.3.3  HTTP serverp. 30
This functional entity acts as the HTTP server for all hypertext transactions.

6.4.3.4  LWP entities |R17|p. 30

6.4.3.4.1  LWP clientp. 30
This functional entity acts as the light-weight protocol client for all transactions of the SEAL client executing in a constrained UE. A SEAL client executing in an unconstrained UE may choose to use the LWP client if it is available.
6.4.3.4.2  LWP proxyp. 30
This functional entity acts as a proxy for transactions between the LWP client and one or more LWP servers. The LWP proxy typically terminates a secure transport protocol (e.g. DTLS, TLS or secure WebSocket) session on LWP-1 reference point with the LWP client of the VAL UE allowing the LWP client to establish a single secure session for transactions with multiple LWP servers that are reachable by the LWP proxy.
The LWP proxy can act as a cross-protocol LWP-HTTP proxy to enable LWP clients to access resources on HTTP servers via the LWP-HTTP-2 reference point.
The LWP proxy terminates LWP-3 reference point that lies between different LWP proxies. It may provide a topology hiding function from LWP entities outside the trust domain of the VAL system.
The LWP proxy can also terminate LWP-HTTP-3 reference point for interworking with another HTTP proxy. In this role it provides cross-protocol mapping and may provide a topology hiding function from HTTP entities outside the trust domain of the VAL system.
The LWP proxy shall be in the same trust domain as the LWP clients and LWP servers that are located within a VAL service provider's network. There can be multiple instances of a LWP proxy e.g. one per trust domain.
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6.4.3.4.3  LWP serverp. 30
This functional entity acts as the LWP server for all LWP transactions of the SEAL server.

6.4.3.5  LWP usage |R17|p. 30

LWP is a generic representation of a light-weight protocol for use in constrained environments. Realizations of the light-weight protocol (LWP) functional entities and reference points to a particular protocol are defined in the annexes of this specification.
LWP is a representation of a protocol to be used by the SEAL service enablers on their respective SEAL-UU reference points when the SEAL client is executing in a constrained UE. In this case the SEAL client should use the LWP-1 reference point with the LWP proxy and should use either the LWP-2 or the LWP-HTTP-2 reference point for transport and routing of the related signalling with the SEAL server.
A SEAL client executing in a non-constrained UE may choose to use the LWP-1 reference point with the LWP proxy and may use either the LWP-2 or the LWP-HTTP-2 reference point for transport and routing of the related signalling with the SEAL server.
LWP may be used for interactions between SEAL servers on their respective SEAL-E reference points. For this usage the SEAL-E reference point shall use the LWP-1 and either the LWP-2 or the LWP-3 reference point depending on the trust relationship between the interacting SEAL servers.
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