10.3 Pre-established session (on-network)

23.2803GPPCommon functional architecture to support mission critical servicesRelease 18Stage 2TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

10.3.1 General

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 IETF RFC 5245 [22], 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.

10.3.2 Procedures

10.3.2.1 General

The pre-established session can be established after MC service authorization for the user (see 3GPP TS 23.379 [16]).

The pre-established session is a session establishment procedure between the MC service client and the MC service server to exchange necessary media parameters needed for the definition of the media bearers. After the pre-established session is established, the media bearer carrying the floor control messages is always active. Additionally, the MC service client is able to activate the media bearer carrying the voice whenever needed:

– immediately after the pre-established session procedure; or

– using SIP signalling when an MC service call is initiated.

10.3.2.2 Pre-established session establishment

The pre-established session is a session between the MC service client and the MC service server in the MC system, and which may utilise other functional entities (e.g. a media distribution function, as defined in subclause 7.4.2.3.5, for means of obtaining media parameters and gathering ICE candidates). Figure 10.3.2.2-1 represents the pre-established session establishment flow.

Figure 10.3.2.2-1: Pre-established session establishment

1. The MC service client within the MC service UE gathers ICE candidates.

2. The MC service client within the MC service UE sends a request to the MC service server to create a pre-established session.

3. MC service server performs necessary service control, obtains media parameters (e.g. by means of interacting with a media distribution function of the MC service server) and gathers ICE candidates.

4. MC service server sends a create pre-establish session response to the MC service client within the MC service UE.

5. ICE candidate pair checks take place e.g. between the MC service client within the MC service UE and a media distribution function of the MC service server.

6. If necessary the MC service client within the MC service UE sends a modify pre-established session request to the MC service server to update the ICE candidate pair for the pre-established session.

7. The MC service server sends a modify pre-established session response accepting the ICE candidate pair update.

The media sessions consist of at least an active media session carrying the media and media control messages and an inactive media session for the media.

10.3.2.3 Pre-established session modification

Figure 10.3.2.3-1 represents the pre-established session modification flow.

Figure 10.3.2.3-1: Pre-established session modification

1. The MC service client within the MC service UE gathers ICE candidates, if necessary (e.g. depending on the information that needs to be updated).

2. The MC service client within the MC service UE sends a request to the MC service server to modify a pre-established session.

3. MC service server performs necessary service control, obtains any necessary media parameters (e.g. by means of interacting with a media distribution function of the MC service server) and gathers necessary ICE candidates.

4. MC service server sends a modify pre-establish session response to the MC service client within the MC service UE.

5. If necessary, ICE candidate pair checks take place e.g. between the MC service client within the MC service UE and a media distribution function of the MC service server.

7. The MC service server sends a modify pre-established session response accepting the ICE candidate pair update.

NOTE 1: The represented procedure corresponds to a session modification initiated by the MC service client. It can also be initiated by the MC service server.

NOTE 2: The procedure can also be used to switch a media session from the inactive to the active state and the reverse. The modification of the session triggers a corresponding modification of the characteristics (e.g. activity, bandwidth) of the corresponding GBR bearers.

10.3.2.4 Pre-established session release

Figure 10.3.2.4-1 represents the MC service client within the MC service UE initiated pre-established session release flow and figure 10.3.2.4-2 represents the MC service server initiated pre-established session release flow.

Figure 10.3.2.4-1: MC service client within the MC service UE initiated pre-established session release

1. The MC service client within the MC service UE sends a request to the MC service server to release a pre-established session.

2. The MC service server sends a release pre-establish session response to the MC service client within the MC service UE.

3. The MC service server releases all resources for the pre-established session.

Figure 10.3.2.4-2: MC service server initiated pre-established session release

1. The MC service server sends a request to the MC service client within the MC service UE to release a pre-established session.

2. The MC service client within the MC service UE sends a release pre-establish session response to the MC service server.

3. The MC service server releases all resources for the pre-established session.