6.3.7 Transmission control server state transition for basic reception control operations towards the transmission participant

24.5813GPPMission Critical Video (MCVideo) media plane controlProtocol specificationRelease 18TS

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

6.3.7.1 General

The reception control interface towards the MCVideo client in the transmission control server shall behave according to the state diagram and state transitions specified in this clause.

Figure 6.3.7.1-1 shows the states and state transitions for an associated transmission participant in the transmission control server.

Figure 6.3.7.1-1: Transmission control server state transition diagram for basic reception control operation towards the transmission participant

The reception control interface towards the MCVideo client in the transmission control server shall create one instance of the ‘basic reception control operations’ state machine towards the MCVideo client for every transmission participant served by the transmission control server as follows:

1. For pre-arranged group call in case of an originating MCVideo call, the ‘basic reception control operation towards the transmission participant’ state machine shall be created when the MCVideo server sends the SIP 200 (OK) response towards the originating MCVideo client.

2. For pre-arranged group call in case of a terminating MCVideo call, the ‘basic reception control operation towards the transmission participant’ state machine shall be created when the transmission control server receives the SIP 200 (OK) response.

3. For chat group call the ‘basic reception control operation state machine towards the transmission participant’ shall be created when the MCVideo server sends the SIP 200 (OK) response to the received initial SIP INVITE request.

The transmission participant associated to the ‘basic reception control operation towards the transmission participant’ state machine is here referred to as the "associated transmission participant".

The external inputs to the state machine are:

1. directives coming from the reception control arbitration logic;

2. transmission control messages sent by the transmission participants;

3. media; and

4. in certain cases, SIP messages used for call handling.

If transmission control messages or RTP media packets arrives in a state where there is no procedure specified in the following clauses, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall discard the transmission control message;

2. shall request the network media interface in the MCVideo server to discard any received RTP media packet; and

3. shall remain in the current state.

State details are explained in the following clauses.

6.3.7.2 State: ‘Start-stop’

6.3.7.2.1 General

When a new instance of the ‘basic reception control operations towards the transmission participant’ state machine is created, before any reception control related input is applied, the state machine is in the ‘Start-stop’ state. Similarly when the call is released the state machine shall return to the Start-Stop state.

An association between the transmission control server and a transmission participant in the MCVideo client is created, when the state machine is created; and

1. in case of an originating MCVideo call, when the MCVideo server sends the SIP 200 (OK) response to the originating MCVideo client; and

2. in case of a terminating MCVideo call, when the transmission control server receives the SIP 200 (OK) response sent from the terminating MCVideo client.

6.3.7.2.2 SIP Session initiated

When a SIP Session is established and if the session is a normal group call session:

NOTE 1: Temporary group call is not supported in this release. Normal group call contains pre-arranged group call, chat group call, broadcast group call.

1. if an MCVideo client initiate an MCVideo call, and the MCVideo call does not exist yet, the transmission control interface towards the MCVideo client in the transmission control server:

a. shall initialize a general state machine as specified in clause 6.3.6.2.2; and

NOTE 2: In the clause 6.3.6.2.2 the ‘general reception control operation’ state machine will continue with the initialization of the ‘general reception control operation’ state machine.

b. shall enter the state ‘U: not permitted to receive’ as specified in the clause 6.3.7.3.2; and

2. if the associated transmission participant attempts to initiate an already existing MCVideo call or MCVideo client rejoins an ongoing MCVideo call or if the MCVideo client is invited to the MCVideo call

a if no MCVideo client has the permission to send media, the transmission control interface towards the MCVideo client in the transmission control server

i. shall enter the state ‘U: not permitted to receive’ as specified in the clause 6.3.7.3.2; and

b if other MCVideo clients have permission to send a media, the transmission control interface towards the MCVideo client in the transmission control server:

i. shall enter the state ‘U: not permitted to receive’ as specified in the clause 6.3.7.3.2; and

ii. shall send media transmission notification as specified in the clause 6.3.7.3.3.

NOTE 3: The usecases, the MCVideo client initiating new call, joining ongoing call and re-joining ongoing call are applicable towards the originating MCVideo client and for other usecases it is applicable towards the terminating MCVideo client.

The maximum reception priority of the transmission participant is permitted to request is negotiated in the "mc_reception_priority" fmtp attribute as specified in clause 14.

6.3.7.3 State: ‘U: not permitted to receive’

6.3.7.3.1 General

The transmission control interface towards the MCVideo client in the transmission control server uses this state when the associated transmission participant is not permitted to receive media.

6.3.7.3.2 Enter state ‘U: not permitted to receive’

When entering this state, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall set the state for the associated transmission participant to ‘U: not permitted to receive’.

2. shall initialise counter C9 (Reception Active) to 0; and

3. shall empty Active SSRC list

6.3.7.3.3 Send Media Transmission Notification message (S: Media Transmission Notification)

When the transmission control server has received RTP media packets from another transmission participant or upon receiving a Media Transmission Notification message from the reception control arbitration logic, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall send the Media Transmission Notification message to the transmission participant;

2. shall include the User ID and the SSRC of user transmitting the media in the Media Transmission Notification message;

3. 3shall include the Functional Alias ID of the transmitting user if received in the Media Transmission Notification;

4. may set the first bit in the subtype of the Media Transmission Notification message to ‘1’ (Acknowledgment is required) as described in clause 9.2.2.1; and

NOTE: It is an implementation option to handle the receipt of the Transmission control Ack message and what action to take if the Transmission control Ack message is not received.

5. if the Reception Mode field is set to ‘0’ indicating automatic reception mode:

a. shall increase C9 (Reception Active) by ‘1’ if it has not reached its upper limit;

b. shall store the SSRC of transmission participant granted the permission to send media in Active SSRC list until the associated transmission is ended towards the participant; and

c. shall enter the state ‘U: permitted to receive’ as specified in clause 6.3.7.4.2; and

6. if the Reception Mode field is set to ‘1’ indicating manual reception mode:

a. shall remain in the ‘U: not permitted to receive’ state as specified in the clause 6.3.7.3.2.

6.3.7.3.4 Reception of Receive Media Request message (R: Receive Media Request)

Upon receiving a Receive Media Request message from the associated transmission participant, the transmission control interface towards the MCVideo client in the transmission control server:

1. if the session is not a broadcast group call, shall forward the Receive Media Request message to the reception control arbitration logic;

2. if the reception control arbitration logic decides that the transmission participant cannot receive media, shall send a Receive Media Response (Rejected) message to the associated transmission participant. The Receive Media Response (Rejected) message:

a. shall include in the Result field the <Result indicator> value result#0 (Rejected)

b. shall include in the Reject Cause field the <Reject Cause> value:

i. cause#0 (Insufficient downlink bandwidth); or

ii. cause#1 (No permission to receive)

c. may include in the Reject Cause field an additional text string explaining the reason for rejecting the Transmission request in the <Reject Phrase> value;

d. may set the first bit in the subtype of the Transmission Response (Rejected) message to ‘1’ (Acknowledgment is required) as described in clause 9.2.2.1; and

NOTE 3: It is an implementation option to handle the receipt of the Transmission control Ack message and what action to take if the Transmission control Ack message is not received.

e. if a group call is a broadcast group call, a system call, an emergency call, an imminent peril call, or a temporary group session, shall include the Transmission Indicator field with appropriate indications; and

3. shall remain in the ‘U: not permitted to receive’ state.

Upon receiving a Receive Media Request messagae from the associated transmission participant including a Reception Priority field, the reception priority shall be the lower of the reception priority included in Receive Media Request message and the negotiated maximum reception priority that the MCVideo client is permitted to request.

6.3.7.3.5 Receive Media Reception End Response message (R: Media Reception End Resonse)

Upon receiving the Media Reception End Response message from the transmission participant, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall release any downlink resources associated with the transmission participant; and

2. shall remain in the ‘U: not permitted to receive’ state.

6.3.7.3.6 Send Receive Media Response (Granted) message (S: Receive Media Response (Granted))

When the reception control arbitration logic in the MCVideo server decides to grant permission to the transmission participant to receive the media, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall send the Receive Media Response (Granted) message to the associated transmission participant;

2. may set the first bit in the subtype of the Receive Media Response (Granted) message to ‘1’ (Acknowledgment is required) as described in clause 9.2.2.1;

NOTE: It is an implementation option to handle the receipt of the Transmission control Ack message and what action to take if the Transmission control Ack message is not received.

3. shall increase C9 (Reception Active) by 1 if it has not reached its upper limit;

4. shall store the SSRC of transmission participant granted the permission to send media in Active SSRC list until the associated transmission is ended towards participant; and

5. shall enter the state ‘U: permitted to receive’ as specified in clause 6.3.7.4.2.

6.3.7.3.7 Send Transmission End Notify message (S: Transmission End Notify)

When transmission control server has stopped receiving RTP media packets from another transmission participant on uplink or upon receiving a Transmission End Notify message from the reception control arbitration logic, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall send the Transmission End Notify message to the transmission participant;

2. shall include the SSRC of the user transmitting the media in the Transmission End Notify message; and

3. shall remain in the ‘U: not permitted to receive’ state.

6.3.7.4 State: ‘U: permitted to receive’

6.3.7.4.1 General

The transmission control interface towards the MCVideo client in the transmission control server uses this state when the associated transmission participant has been given permission to receive media.

6.3.7.4.2 Enter state ‘U: permitted to receive’

When entering this state the transmission control interface towards the MCVideo client in the transmission control server:

1. shall set the state for the associated transmission participant to ‘U: permitted to receive’.

6.3.7.4.3 Send RTP media packets (S: RTP media)

Upon the decision of the reception control arbitration logic to permit the transmission participant to receive a media in transmission, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall request the network media interface in the MCVideo server to forward RTP media packets to the media distributor in the MCVideo server if received packet SSRC is present in the Active SSRC list;

2. shall discard the RTP media packets if received packet SSRC is not in the Active SSRC list; and

3. shall remain in the ‘U: permitted to receive’ state.

6.3.7.4.4 Receive Media Reception End Request message (R: Media Reception End Request)

Upon receiving a Media Reception End Request message from the associated transmission participant, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall forward the Media Reception End Request message to the general transmission control operation state machine of the transmission control arbitration logic in the MCVideo server; and

2. shall remain in the ‘U: permitted to receive’ state.

6.3.7.4.5 Send Media Transmission Notification message (S: Media Transmission Notification)

When transmission control server has received RTP media packets from another transmission participant on uplink or upon receiving a Media Transmission Notification message from the reception control arbitration logic, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall send the Media Transmission Notification message to the transmission participant;

2. shall include the User ID and the SSRC of user transmitting the media in the Media Transmission Notification;

3. may set the first bit in the subtype of the Media Transmission Notification message to ‘1’ (Acknowledgment is required) as described in clause 9.2.2.1;

NOTE: It is an implementation option to handle the receipt of the Transmission control Ack message and what action to take if the Transmission control Ack message is not received.

4. if the Reception Mode field is set to ‘0’ indicating automatic reception mode:

a. shall increase C9 (Reception Active) by ‘1’ if it has not reached its upper limit; and

b. shall store the SSRC of transmission participant granted the permission to send media in Active SSRC list until the associated transmission is ended towards participant;

5. shall include the Functional Alias ID of the transmitting user if it is included in the received Media Transmission Notification message; and

6. shall remain in the ‘U: permitted to receive’ state.

6.3.7.4.6 Send Media Reception Override Notify message (S: Media Reception Override Notify)

When transmission control server has received RTP media packets from another transmission participant on uplink and the transmission control server decides that it cannot send the RTP media packet on downstream even if the user if permitted to receive, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall send the Media Reception Override Notify message to the transmission participant;

2. shall include the SSRC of the user transmitting the media in the Media Reception Override Notify message; and

3. shall remain in the ‘U: permitted to receive’ state.

6.3.7.4.7 Send Transmission End Notify message (S: Transmission End Notify)

1. shall send the Transmission End Notify message to the transmission participant;

2. shall include the SSRC of the user transmitting the media in the Transmission End Notify message;

3. if SSRC of the user transmitting the media present in Active SSRC list then shall decrease C9 (Reception Active) by 1 if it has not reach its lower limit;

4. shall remove SSRC of the user transmitting the media from Active SSRC list; and

5. if C9 has not reached it lower limit, shall remain in the ‘U: permitted to receive’ state; or

6. if C9 has reached it lower limit, shall enter the ‘U: not permitted to receive’ state as specified in clause 6.3.7.3.2.

6.3.7.4.8 Send Media Reception End Request message (S: Media Reception End Request)

When the transmission control server determines to end sending the RTP media packets on downlink to the transmission participant, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall stop sending the RTP media packets to the transmission participant;

2. shall send the Media Reception End Request message to the transmission participant;

3. shall include the SSRC of the user transmitting the media in the Media Reception End Request message; and

4. shall enter the ‘U: not permitted to receive’ state.

6.3.7.4.9 Send Media Reception End Response message (S: Media Reception End Response)

1. shall stop sending the RTP media packets to the transmission participant;

2. shall send the Media Reception End Response message to the transmission participant, may set the first bit in the subtype of the Media Reception End Response message to ‘1’ (Acknowledgment is required) as described in clause 9.2.2.1;

NOTE 3: It is an implementation option to handle the receipt of the Transmission control Ack message and what action to take if the Transmission control Ack message is not received.

3. if SSRC of the user transmitting the media present in Active SSRC list then shall decrease C9 (Reception Active) by 1 if it has not reach its lower limit;

4. shall remove SSRC of the user transmitting the media from Active SSRC list; and

5. if C9 has not reached it lower limit, shall remain in the ‘U: permitted to receive’; or

6. if C9 has reached it lower limit, shall enter the ‘U: not permitted to receive’ state as specified in clause 6.3.7.3.2.

6.3.7.4.10 Reception of Receive Media Request message (R: Receive Media Request)

Upon receiving a Receive Media Request message from the associated transmission participant, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall reject the request if following condition is fulfilled and shall skip the forwarding of Receive Media Request message to the reception control server aribitration logic:

a. if the counter C9 (Reception Active) has reached its upper limit;

2. if the session is not a broadcast group call, shall forward the Receive Media Request message to the reception control server arbitration logic;

3. if the reception control server arbitration logic decides that the transmission participant cannot receive media, shall send a Receive Media Response (Rejected) message to the associated transmission participant. The Receive Media Response (Rejected) message:

a. shall include in the Result field the <Result indicator> value result#0 (Rejected)

b. shall include in the Reject Cause field the <Reject Cause> value:

i. cause#0 (Insufficient downlink bandwidth); or

ii. cause#1 (No permission to receive) ; or

iii. cause#7 (Max no of simultaneous stream to receive is reached); and

c. may include in the Reject Cause field an additional text string explaining the reason for rejecting the Transmission request in the <Reject Phrase> value;

d. may set the first bit in the subtype of the Transmission Response (Rejected) message to ‘1’ (Acknowledgment is required) as described in clause 9.2.2.1; and

NOTE 3: It is an implementation option to handle the receipt of the Transmission control Ack message and what action to take if the Transmission control Ack message is not received.

4. shall remain in the ‘U: permitted to receive’ state.

Upon receiving a Receive Media Request message from the associated transmission participant including a Reception Priority field, the reception priority shall be the lower of the reception priority included in Receive Media Request message and the negotiated maximum reception priority that the MCVideo client is permitted to request.

6.3.7.4.11 Send Receive Media Response (Granted) message (S: Receive Media Response (Granted))

When the reception control server arbitration logic in the MCVideo server decides to grant permission to the transmission participant to receive the media, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall send the Receive Media Response (Granted) message to the associated transmission participant;

2. may set the first bit in the subtype of the Receive Media Response (Granted) message to ‘1’ (Acknowledgment is required) as described in clause 9.2.2.1; and

NOTE: It is an implementation option to handle the receipt of the Transmission control Ack message and what action to take if the Transmission control Ack message is not received.

3. shall increase C9 (Reception Active) by 1 if it has not reach its upper limit;

4. shall store the SSRC of transmission participant granted the permission to send media in Active SSRC list until the associated transmission is ended towards participant; and

5. shall remain in the ‘U: permitted to receive’ state.

6.3.7.4.12 Receive Media Reception End Response message (R: Media Reception End Response)

Upon receiving the Media Reception End Response message from the transmission participant, the transmission control interface towards the MCVideo client in the transmission control server:

1. shall release any downlink resources associated to requested media reception to be ended for the transmission participant; and

2. shall remain in the ‘U: permitted to receive’ state.