Content for  TS 23.281  Word version:  20.0.0

The procedure is for providing transmission control to MCVideo UE in an off-network case. Transmission control is performed by using transmission control information flows between the transmission control participant and the transmission control arbitrator. The transmission control arbitrator is a member MCVideo UE of the MCVideo group where the transmission rules are applied. Off-network transmission control is based on ProSe capabilities as described in clause 7.18. Transmission control in off-network can be performed in two ways:

• Single arbitrator: transmission participants rely on a single participant designated as transmission arbitrator for the arbitraton of transmission requests.
• Self arbitration: each transmsission participant arbitrates its own transmission based on its view of the topology.

Both of the approaches, as appropriate for the deployment model, can be adopted for MCVideo group using a configurable parameter (as defined in Annex A.4). In the single arbitrator approach, one MCVideo client assumes the responsibility for arbitration of transmission requests for all group members within range. All requests for transmission are directed to the arbitrator, and the arbitrator checks the configured limits on the simultaneous transmissions, and grants or denies the request. If an MCVideo client is out of range of the current arbitrator, the MCVideo client is allowed to transmit and also become a transmission arbitrator. If there is insufficient capacity to carry an extra transmission i.e. the configured limit for simultaneous transmissions is reached, the MCVideo client may request that an existing transmitting MCVideo client is pre-empted; the pre-emption request is sent to the transmission arbitrator. In the self arbitration approach, each MCVideo client decides for itself whether there is sufficient capacity to carry the transmission. If it determines that there is insufficient capacity i.e. the configured limit for simultaneous transmissions is reached, and from its perspective another transmitting MCVideo client has a lower priority, the requesting MCVideo client may send an override request directly to this other transmitting MCVideo client, which will either accept the override request and give way, or deny the override request. In both the single arbitrator approach and the self arbitration approach, if there is insufficient capacity to carry the communication i.e. the configured limit on the simultaneous transmissions is reached, the MCVideo client may report this to the MCVideo user. The MCVideo user may decide to transmit anyway, and instruct the MCVideo client to proceed with the transmission. Further subclauses apply to one or both of the single arbitrator approach and the self arbitration approach. Applicability is explicitly indicated in each of the relevant subclauses.

This subclause is applicable only in single arbitrator approach. Figure 7.7.2.3-1 describes procedures for transmission participants when an MCVideo client initializes transmission control. The MCVideo client sends a transmission request to detect presence of a transmission arbitrator. If the MCVideo client does not receive a response to the transmission request, it sends a transmission arbitration taken message and becomes the transmission arbitrator. The MCVideo client may now transmit a video. This procedure applies when either there have been no recent MCVideo transmissions within the MCVideo group and therefore no arbitrator has been selected, or where there have been recent MCVideo transmissions which may still be ongoing, but the arbitrator cannot be reached, e.g. where MCVideo client that wants to transmit video has gone out of range of the arbitrator. Pre-conditions:

1. An off-network group communication has been established.
2. MCVideo client 1 wishes to transmit video, and has determined that the pre-configured limit on the number of transmissions within the MCVideo group has not been reached.

This subclause is applicable only in self arbitration approach. Figure 7.7.2.3a-1 describes procedures for transmission participants when an MCVideo client initializes transmission control. Pre-conditions:

1. An off-network group communication has been established.
2. MCVideo client 1 wishes to transmit video.

This subclause is applicable only in single arbitrator approach. Figure 7.7.2.4-1 describes procedures for transmission participants when an MCVideo client requests for transmission permission. The MCVideo client has detected presence of a transmission arbitrator e.g., by receiving responses to transmission arbitration control message. The MCVideo client sends a transmission request and waits for a response. The MCVideo client upon receiving a transmission granted message may transmit a video. Pre-conditions:

1. An off-network group communication has been established.
2. At least one participant is currently transmitting video.

This subclause is applicable only in single arbitrator approach. Figure 7.7.2.5-1 describes procedures for transmission participants when an MCVideo client requests for transmission permission. The MCVideo client has detected presence of a transmission arbitrator e.g., by receiving responses to transmission arbitration control message. The MCVideo client sends a transmission request and waits for a response. Pre-conditions:

1. An off-network group communication has been established.
2. At least one participant is currently transmitting video.

This subclause is applicable in both the single arbitrator and self arbitration approaches. Figure 7.7.2.6-1 describes procedures for transmission participants when an MCVideo client releases transmission permission. The MCVideo client has detected presence of a transmission arbitrator e.g., by receiving responses to transmission arbitration control message. The MCVideo client stops the video transmission and sends a transmission release request. Pre-conditions:

1. An off-network group communication has been established.
2. MCVideo client has requested transmission permission and may have received transmission permission.

This subclause is applicable in the single arbitrator in the approach. Figure 7.7.2.7-1 describes procedures for transmission participants when an MCVideo client authorized to override, requests for transmission permission. The MCVideo client has detected presence of a transmission arbitrator e.g., by receiving responses to transmission arbitration control message. The MCVideo client sends a transmission request and waits for a response. Pre-conditions:

1. An off-network group communication has been established.
2. Maximum simultaneous transmissions limit has been reached.

This subclause is applicable in the single arbitrator approach. Figure 7.7.2.8-1 describes procedures for transmission participants when an MCVideo client authorized to override, requests for transmission permission. The MCVideo client has detected presence of a transmission arbitrator e.g., by receiving responses to transmission arbitration control message. The MCVideo client sends a transmission request and waits for a response. Pre-conditions:

1. An off-network group communication has been established.
2. Maximum simultaneous transmissions limit has been reached.

This subclause is applicable in both the single arbitrator and self arbitration approaches. Figure 7.7.2.10-1 describes procedures for transmission participants when simultaneous transmission requests are generated when more than one MCVideo client initializes transmission control. Figure 7.7.2.10-1 shows the expected behaviour if simultaneous transmission requests are generated in the following scenarios:

• a single arbitrator approach is used but there is currently no arbitrator; or
• self arbitration is used.

Pre-conditions:

1. An off-network group communication has been established.
2. MCVideo client 1 has higher transmission priority than MCVideo client 2.