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Content for  TS 23.280  Word version:  18.1.0

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11  MC gateway UE |R18|Word‑p. 259

11.1  GeneralWord‑p. 260

An MC gateway UE enables MC service access for a MC service user residing on non-3GPP capable devices and for devices which are unable to host MC service clients. In order to be able to participate in a MC service, the MC gateway UE provides the following necessary functions to enable the MC service access for such MC clients:
  • MC gateway client to MC gateway association: Authorised binding and use of non-3GPP based access with an MC service client. Indicate associated MC gateway clients when the MC gateway UE cannot serve the connected MC service clients (any longer).
  • 3GPP transport resources: Sharing of MC gateway UE 3GPP transport resources among the associated MC service clients.
  • MC client identification: Independent MC service client identification, MC service client authorisation and MC service profile association.
  • Location Management: Providing location management support for the associated MC clients to handle the location information and triggers related to 3GPP access network.
  • MC client communication integrity: Ensure that signalling, media content and traffic attributes, e.g. priority and QoS, of communications between the MC system and MC service client remains unaltered.
The following functions are provided by the MC gateway client:
  • MC gateway association: Allowing an MC gateway client to simultaneously bind to multiple MC gateway UEs.
  • MC service selection: Choose between multiple MC gateway UEs for the required MC service capability.
  • MC service continuation: Enables reselection of the MC gateway UE association while MC service continues.
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11.2  Functional ModelWord‑p. 260

11.2.0  GeneralWord‑p. 260

The MC gateway UE offers access to the MC server for several MC clients as shown in Figure 11.2.0-1). The MC clients can be either located in the MC gateway UE or in non-3GPP devices connected to the MC gateway UE via non-3GPP access.
For non-3GPP devices which can host an MC client, the MC gateway UE enables connectivity to the MC server. For non-3GPP devices which cannot host the MC client, the MC gateway UE hosts the instantiation of the MC client for the non-3GPP device.
Copy of original 3GPP image for 3GPP TS 23.280, Fig. 11.2.0-1: Functional architecture
Figure 11.2.0-1: Functional architecture
(⇒ copy of original 3GPP image)
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The MC gateway UE provides MC service capabilities and 3GPP access capabilities using 3GPP network credentials for authorized access with an MC server.
For non-3GPP devices which cannot host MC clients, the MC gateway UE shall control the access and manage the communication between the non-3GPP devices and the MC server. Upon reception of connection authorization request from a non-3GPP device, the MC gateway UE instantiates an MC client, acting on behalf of the non-3GPP device, to provide the requested services (e.g. emergency call, group calls, short data messages services, etc.). The communication interworking and the definition of associated procedures between the MC client (initiated at the MC gateway UE) and the non-3GPP devices is out of scope of this document.
For MC clients getting MC service access via the MC gateway UE, the MC gateway UE forwards (unmodified) signalling and media from the individual MC clients to the MC server and vice versa.
If the MC service user on the non-3GPP device utilizes multiple MC services simultaneously, the MC service access may also be provided by one or multiple MC gateway UEs as shown in Figure 11.2.0-2 while restricting each MC service to one MC gateway UE (e.g. MCPTT via MC gateway UE1, MCData via MC gateway UE2).
Copy of original 3GPP image for 3GPP TS 23.280, Fig. 11.2.0-2: Simultaneous multiple MC gateway UE use by a single non-3GPP device
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11.2.1  Functional modelWord‑p. 262

For the application-level signalling necessary for the association between the MC client on the non-3GPP device and the MC gateway UE reference point Gateway-local (GW-local) is used. The MC gateway UE uses the Gateway-Core (GW-Core) reference point towards the MC service server to announce the association between MC gateway client and MC gateway UE server. Once the use of the MC gateway UE has been authenticated and authorized by the corresponding MC service server, the MC service user is authorized MC gateway user.
The MC gateway UE sever enables the following functions:
  • Authentication of the MC gateway clients including the MC gateway UE function of the corresponding MC service server
  • Relay of signalling between MC client and MC service server/CSC server
  • Relay of signaling between the signaling user agent residing on the non-3GPP device and the SIP core
  • Relay of signaling between the HTTP client residing on the non-3GPP device and the HTTP proxy
  • Media plane forwarding between the MC servive server and the MC clients
The MC gateway UE function as part of the corresponding MC service server enables the use of an MC gateway UE with a corresponding MC gateway UE function that authorizes the association between the MC gateway client/MC client and the corresponding MC gateway UE to enable forwarding of the media plane to MC clients via the MC gateway UE.
Copy of original 3GPP image for 3GPP TS 23.280, Fig. 11.2.1-1: Functional model of MC gateway UE signalling plane
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11.2.2  Reference pointsWord‑p. 263

11.2.2.1  GeneralWord‑p. 263

The reference points for the use of the MC gateway UE are described in the following subclauses.

11.2.2.2  Reference point GW-local (between the MC gateway client and the MC gateway UE)Word‑p. 263

The GW-local reference point between the MC gateway client and the MC gateway UE is used:
  • To authorise the use of the MC gateway UE,
  • To manage (request/release) forwarding of the signalling, media from the MC gateway UE to the MC gateway client and its associated MC clients for unicast, multicast/broadcast communication using corresponding identifiers, e.g., TMGI.

11.2.2.3  Reference point GW-Core (between the MC gateway UE and the MC service server)Word‑p. 263

The GW-Core reference point between the MC gateway UE and the MC service server shall be used:
  • To authorise the use of the MC gateway UE by the corresponding MC service server.
  • To manage (request/release) transport resources between the MC gateway UE and the MC service server signalling purposes are associated with the MC clients residing on a non-3GPP device.
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11.2.2.4  Reference points CSC-n, SIP-1 and HTTP-1Word‑p. 264

The reference points CSC-n belonging to the application plane and the reference points SIP-1 and HTTP-1 belonging to the signaling control plane are relayed by the MC gateway UE between MC client on the non-3GPP device towards the MC gateway UE and the corresponding MC service server.
CSC-n, SIP-1 and HTTP-1 reference points are specified in the present specification. The MCX-n reference points are specified in TS 23.379, TS 23.281 and TS 23.282.
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11.2.3  Media plane aspectsWord‑p. 264

The MC gateway UE forms the relay unit for the media plane between MC server and MC client using 3GPP transport resources on one hand and non-3GPP transport resources on the other hand. The media forwarding function relays the media traffic for unicast and multicast/broadcast between the 3GPP connectivity and non-3GPP connectivity following the media forwarding request controlled by the MC gateway UE server. For the use of unicast media and multicast/broadcast media the corresponding reference points of the respective MC service applies. The corresponding media parameter applies between the respective service dependent media function and service dependent media distribution function.
Copy of original 3GPP image for 3GPP TS 23.280, Fig. 11.2.3-1: Function Model of MC gateway UE media plane
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11.3  Using identities behind the MC gateway UEWord‑p. 264

11.3.1  GeneralWord‑p. 264

The MC gateway UE enables access to the MC system for MC service clients either hosted on the MC gateway UE or hosted on non-3GPP devices using non-3GPP connectivity with the MC gateway UE. Simultaneous sharing of an MC gateway UE by multiple MC service clients requires a unique relationship between the MC service identities used by the MC service clients with corresponding media streams passing the MC gateway UE towards the MC system sharing 3GPP connectivity of the MC gateway UE.
A MC service user behind the MC gateway UE has no 3GPP transport access credentials (i.e., no UICC), whereas the MC system relies on private user identity associated with public user identities (i.e., IMPUs/IMPIs) needed for authentication purposes. Moreover, the one-to-one correspondence between MC service ID and IMPUs enables routing of signalling traffic between the MC service server and the MC service client.
The use of the various mission critical user identities is determined by clause 8 of the present document.
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11.3.2  When using separate IMS subscriptionsWord‑p. 265

If the MC service clients are hosted by non-3GPP devices or the MC service clients are hosted by the MC gateway UE, an MC service user corresponding to an MC client uses a dedicated IMS/SIP subscription without any relation to the MC gateway UE subscription.
Figure 11.3.2-1 depicts the use of the IMS Credential (IMC) application in accordance with TS 23.228.
Copy of original 3GPP image for 3GPP TS 23.280, Fig. 11.3.2-1: Using separate IMS subscriptions
Figure 11.3.2-1: Using separate IMS subscriptions
(⇒ copy of original 3GPP image)
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The MC service user profiles are independent of the MC gateway MC service user profile.

11.3.3  When sharing MC gateway UE's IMS subscriptionWord‑p. 265

The MC service clients rely on MC service IDs provided by the MC gateway UE. In this case, the MC service clients behind the MC gateway UE share the credentials from the IMS subscription of the MC gateway UE, as shown in Figure 11.3.3-1. The number of MC service clients behind the MC gateway UE is determined by the number of subscribed MC service IDs that are associated with the IMS subscription of the MC gateway UE.
Copy of original 3GPP image for 3GPP TS 23.280, Fig. 11.3.3-1: Sharing the MC gateway UE's IMS subscription
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11.4  MC gateway UE routing capabilitiesWord‑p. 266

11.4.1  GeneralWord‑p. 266

The use of the MC gateway UE requires the support of an IP network behind the MC gatway UE, that a range of IP addresses are reachable over a single MC gateway UE. That enables the forwarding of signalling information and media plane between no-3GPP devices and MC server by the MC gateway UE.

11.4.2  MC client IP address associationWord‑p. 266

The use of a unique IP address by the MC clients shall be ensured for the period of association of the MC clients via the MC gateway UE with the IMS/SIP core and the MC server. Each MC gateway UE requires a unique local IP address range for their MC client association which is known by the MC service environment and a correlation between the MC client's IP address and the MC gateway UE's IP address exists.
Copy of original 3GPP image for 3GPP TS 23.280, Fig. 11.4.2-1: MC client uses local IP address
Figure 11.4.2-1: MC client uses local IP address
(⇒ copy of original 3GPP image)
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Framed routing in accordance with RFC 2865, RFC 3162, TS 23.501 shall be used to enable the support of an IP network behind the MC gateway UE, such that a range of IP addresses is reachable over a single 3GPP transport session. It allows the routing of packets to IP addresses that do not belong to the PDN/PDU session of the MC gateway UE.
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