Content for  TS 23.280  Word version:  19.0.1

A pre-established session is a session established between an MC service client and the MC service server, on a per MC service basis, to exchange necessary media parameters needed for the definition of media bearers, allowing a faster set-up of MC service calls/sessions. After a pre-established session is established, a media bearer carrying the media and media control messages is always active. The MC service client establishes one or more pre-established sessions to an MC service server after SIP registration, and prior to initiating any MC service related procedures (e.g. calls, sessions) to other MC service users. When establishing a pre-established session, the MC service client negotiates the media parameters, including establishing IP addresses and ports using interactive connectivity establishment (ICE) as specified in RFC 5245, which later can be used in MC service calls/sessions. This avoids the need to negotiate media parameters (including evaluating ICE candidates) and reserving bearer resources during the MC service call/session establishment that results in delayed MC service call/session establishment. The use of pre-established session on the origination side is completely compatible with the use of on demand session on the termination side. The use of pre-established session on the termination side is completely compatible with the use of on demand session on the origination side. The pre-established session may be modified by the MC service client and the MC service server using the SIP procedures for session modification. The pre-established session may be released by the MC service client and the MC service server using the SIP procedures for terminating a SIP session.

A simultaneous session is functionality whereby the MC service client can receive the media from multiple MC service calls/sessions over the same SIP session and media bearer(s) between the MC service client and the MC service server.

The MC service shall support the capability for UE-to-network relay to restrict the relayed group communication on a per group basis. To meet the above requirement, ProSe (as specified in TS 23.303) can be used with an appropriate relay service code as per the following:

• To restrict connection from only the membership of allowed MC service groups, UE-to-network relay UE is provisioned with relay service code(s) associated with allowed MC service group(s). The UE-to-network relay performs the access control as follows:
  1. The UE broadcasts which MC service group(s) is/are authorized to connect to the network over this UE-to-network relay by including the related relay service code(s) in the UE-to-Network Relay Discovery Announcement message (as specified in TS 23.303); or
  2. The UE determines whether to respond to a remote UE's broadcasting message by checking if the relay service code carried in the UE-to-Network Relay Discovery Solicitation message is within the list of allowed relay service codes.
• To find a permitted UE-to-network relay, a remote UE is provisioned with the relay service code(s) associated MC service group(s) which the MC service user belongs to. The remote UE performs the UE-to-network relay selection as follows:
  1. The remote UE determines if it is allowed to connect to a particular UE-to-network relay by checking whether the relay service code(s) associated with its MC service group(s) is/are carried in UE-to-Network Relay Discovery Announcement message (as specified in TS 23.303; or
  2. The remote UE includes the relay service code(s) associated with its MC service group(s) in Network Relay Discovery Solicitation message (as specified in TS 23.303).

The ProSe UE-to-network relay provides a purely layer 3 IP data routing service, when the remote UE loses the coverage of cellular network and the MC service user on the remote UE requires to access the MC service via a ProSe UE-to-network relay. The application layer signalling for the MC service user on a remote UE are identical to the application layer signalling for the MC service user on an on-network UE.