A.5 Pre-established session signalling flows

24.3803GPPMission Critical Push To Talk (MCPTT) media plane controlProtocol specificationRelease 18TS

A.5.1 General

In the following clauses signalling flows are presented for sample procedures related to the call setup and the call release when pre-established session is used.

The behaviour of an originating and terminating client is specified in clause 9.2. The behaviour of the participating MCPTT function is specified in clause 9.3

The behaviour of the controlling MCPTT function is specified in 3GPP TS 24.379 [2]

Only the names of the messages are indicated on the signal flow arrows. The information elements of each message can be found in clause 9.2 and clause 9.3 for media plane control messages and in 3GPP TS 24.379 [2] for SIP messages.

The signalling flow diagrams also indicate the state of the MCPTT client and the participating MCPTT function in the state machines specified in clause 9.2 and clause 9.3 respectively.

When the call initialization is accepted additional floor control dialogue is also indicated in the signalling flow.

The following signalling flows are provided:

1. call initialization at the originating side when the initialization is accepted (clause A.5.2.1);

2. call initialization at the originating side when the initialization is rejected (clause A.5.2.2);

3. call initialization at the termination side when call is accepted (clause A.5.2.3); and

4. call release (clause A.5.3).

A.5.2 Call Initialization

A.5.2.1 Originating Side when initialization accepted

Figure A.5.2.1-1 illustrates the flow of MCPT and MCPC messages when the call initiation request sent by an originating MCPTT client is accepted by the controlling MCPTT function. In this diagram it is assumed that the call initiation request includes implicit floor request.

Figure A.5.2.1-1: Call initialization accepted; originating side

One of the users with a pre-established session initiates a call and the call is accepted by the controlling MCPTT function. Steps 1 to 5 are conducted using SIP messages (see 3GPP TS 24.379 [2]).

1. A pre-established session is created between the origination MCPTT user and the participating MCPTT server. The MCPTT client is in ‘U: Pre-established session not in use" state and the participating MCPTT function is in ‘G: Pre-established session not in use’ state.

2. The origination MCPTT client initiates a call as described in 3GPP TS 24 379 [2] by sending a SIP REFER message. The participating MCPTT function enters into ‘G: Pre-established session in use’ state.

3. The participating MCPTT function sends SIP 200 (OK) to the originating MCPTT client and then the originating MCPTT client enters into ‘U:Pre-established session in use’ state.

4-5.The participating MCPTT function sends a SIP INVITE message to the controlling MCPTT function and receives the SIP 200 (OK) response from the controlling MCPTT function.

6. The participating MCPTT server sends a ‘Connect’ message to the Originating MCPTT client.

7. The originating MCPTT client responds with an Acknowledge (accepted) message.

8. The controlling MCPTT server grants the floor to the originating MCPTT client by sending a Floor Granted message

9. The participating MCPTT server forwards the Floor Granted message to the originating MCPTT client

10. The originating MCPTT clients starts sending the media packets.

11. The participating MCPTT server forwards the media packets to the controlling MCPTT server.

A.5.2.2 Originating Side when initialization rejected

Figure A.5.2.2-1 illustrates the flow of MCPC messages when the call initiation request by an originating MCPTT client is rejected.

Figure A.5.2.2-1: Call initialization rejected

One of the users with a pre-established session initiates a call and the call is rejected by the controlling MCPTT function. Steps 1- 5 are conducted using SIP messages (see 3GPP TS 24.379 [2]).

1. A pre-established session is created between the origination MCPTT client and the participating MCPTT server. The MCPTT client is in ‘U:Pre-established session not in use" state and the participating MCPTT function is in ‘G: Pre-established session not in use’ state.

2. The origination MCPTT client initiates a call as described in 3GPP TS 24.379 [2] by sending a SIP REFER message.The participating MCPTT function enters into ‘G:Pre-established session in use’ state.

3. The participating MCPTT function sends SIP 200 (OK) to the originating MCPTT client and then the originating MCPTT client enters into ‘U:Pre-established session in use’ state.

4-5.The participating MCPTT function sends a SIP INVITE message to the controlling MCPTT function and receives SIP 4xx response from the controlling MCPTT function. The participating MCPTT function enters into ‘G: Call Releasing’ state.

6. The participating MCPTT server sends a Disconnect message to the originating MCPTT client. The originating MCPTT client enters into ‘U: Pre-established session not in use’ state.

7. The originating MCPTT client responds with an Acknowledge message. After receiving the Acknowledge message the participating MCPTT function enters into ‘G:Pre-established session not in use’ state.

A.5.2.3 Termination Side when call initialization accepted

Figure A.5.2.3-1 illustrates the flow of MCPC and MCPT messages when the call initiation is informed to the terminating MCPTT client. In this figure it is assumed that the call initiation request includes implicit floor request. Although the figure shows only one terminating MCPTT client, the messaging takes place with each one of the terminating MCPTT clients with a pre-established session.

Figure A.5.2.3-1: Call initialization accepted; terminating side

When a call initiation is accepted by the controlling MCPTT function, the terminating MCPTT client(s) with pre-established session is (are) informed. Steps 1 to 3 are conducted using SIP messages (see 3GPP TS 24.379 [2]).

1. A pre-established session is created between the terminating MCPTT user and the participating MCPTT server. The MCPTT client is in ‘U: Pre-established session not in use" state and the participating MCPTT function is in ‘G: Pre-established session not in use’ state.

2. The controlling MCPTT server informs the participating MCPTT server the call initiation by sending an SIP INVITE message. The participating MCPTT function enters into ‘G: pre-established session in use’ state.

3. The participating MCPTT function sends SIP 200 (OK) to the controlling MCPTT function.

4. The participating MCPTT function sends a Connect message to the terminating MCPTT client.

5. The terminating MCPTT client responds with an Acknowledge message. The terminating MCPTT client enters into ‘U:Pre-established session in use’ state.

6. The controlling MCPTT server informs that the floor is granted to another MCPTT client by sending a Floor Taken message

7. The participating MCPTT server forwards the Floor Taken message to the originating MCPTT client

8. The controlling MCPTT server starts distributing the media packets sent by the talking MCPTT client.

9. The participating MCPTT server forwards the media packets to the terminating MCPTT client.

A.5.3 Call release

Figure A.5.3-1 illustrates the flow of MCPC messages when the call is released but the pre-established session used by this call is preserved.

Figure A.5.3-1: Call release for a call with pre-established session

A call with a pre-established session is released by preserving the pre-established session used by this call. Steps 2 and 3 are conducted using SIP messages (see 3GPP TS 24.379 [2]).

1. A call using a pre-established session is being conducted. The MCPTT client is in ‘U:Pre-established session in use’ state and the participating MCPTT function is in ‘G: Pre-established session in use’ state.

2. The call release decision is taken by the controlling MCPTT function and informed to the participating MCPTT function as described in 3GPP TS 24.379 [2] by sending a SIP BYE message.

3. The participating MCPTT function sends an SIP ACK message to the controlling MCPTT function and enters into ‘G: Call Releasing’ state.

4. The participating MCPTT server sends a Disconnect message to the MCPTT client of this pre-established session.

5. The MCPTT client sends an Acknowledge message to the participating MCPTT server. The MCPTT client enters to ‘U: Pre-established session not in use’ state and the participating MCPTT function is in ‘G: Pre-established session not in use’ state.

6. The pre-established session between the MCPTT client and the participating MCPTT server is preserved.