7.10 Use of MBMS transmission (on-network)

23.2813GPPFunctional architecture and information flows to support Mission Critical Video (MCVideo)Release 18Stage 2TS

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

7.10.1 Information flows for MBMS Transmission

7.10.1.1 General

Information flows for generic MBMS procedures are defined in 3GPP TS 23.280 [6].

7.10.1.2 MapGroupToBearer

Table 7.10.1.2-1 describes the information flow to associate a MCVideo group call to a MBMS bearer. It is sent from the MCVideo server to the MCVideo client.

Table 7.10.1.2-1: MapGroupToBearer

Information element	Status	Description
MCVideo group ID	M	This element identifies the MCVideo group, in which the call is started.
Media stream identifier (video)	M	This element identifies the media stream of the SDP used for the Video group call (e.g. MBMS subchannel).
Media stream identifier (audio)	O	This element identifies the audio media stream of the SDP used for the Video group call (e.g. MBMS subchannel). This is used if separate codecs are used for video and audio.
TMGI (see NOTE)	O	The MBMS bearer identifier if the media of the MCVideo group call is not sent on the same MBMS bearer as this MapGroupToBearer message.
Call acknowledgement indicator	O	Indication that the MCVideo group call requires acknowledgement from receiving MCVideo clients.
NOTE: TMGI shall be present if this message is sent over a different MBMS bearer than the media of the group call; TMGI may be present if this message is sent over the same MBMS bearer as the media of the group call.

7.10.1.3 UnmapGroupFromBearer

Table 7.10.1.3-1 describes the information flow to disconnect a MCVideo group call from a MBMS bearer. It is sent from the MCVideo server to the MCVideo client.

Table 7.10.1.3-1: UnmapGroupFromBearer

Information element	Status	Description
MCVideo group ID	M	This element identifies the MCVideo group which will no longer use the MBMS bearer.

7.10.2 Use of pre-established MBMS bearers

The MCVideo service shall support the procedure for using pre-established MBMS bearers as specified 3GPP TS 23.280 [6] with the following clarifications:

– The MC service client is the MCVideo client;

– The MC service server is the MCVideo server; and

– The MC service ID is the MCVideo ID.

The MCVideo service shall use the MCVideo-1, MCVideo‑8 and MCVideo-9 reference points for this procedure.

MCVideo may use pre-established MBMS bearer for the different types of MCVideo group calls. Both pre-arranged group calls and chat group calls can use the pre-established MBMS bearer for distributing the media. The MBMS bearer can be used by any group. Depending on the capacity of the MBMS bearer, the bearer can be used to broadcast one or more group calls in parallel.

Both the media packets as well as the transmission control messages to the receiving MCVideo clients are sent on the MBMS bearer. Optionally a separate MBMS bearer could be used for the transmission control messages, due to different bearer characteristic requirements.

When using the pre-established MBMS bearer for MCVideo, the MCVideo server perform the procedure of call connect and disconnect over MBMS as defined in subclause 7.10.4 at the group communication session establishment step.

7.10.3 Use of dynamic MBMS bearer establishment

The MCVideo service shall support the procedure for using dynamic MBMS bearers as specified 3GPP TS 23.280 [6] with the following clarifications:

– The MC service client is the MCVideo client;

– The MC service server is the MCVideo server; and

– The MC service ID is the MCVideo ID.

The MCVideo service shall use the MCVideo-1, MCVideo-4, MCVideo-7, MCVideo-8 and MCVideo-9 reference points for this procedure.

MCVideo may use dynamic MBMS bearer establishment for the different types of MCVideo group calls. Both pre-arranged group calls and chat group calls can use the dynamic MBMS bearer for distributing the media.

Both the media packets as well as the transmission control messages to the receiving MCVideo clients are sent on the MBMS bearer.

When using the procedures for dynamic MBMS bearer establishment for MCVideo, the MCVideo server perform the procedure of mapping group communication to MBMS bearer as defined in subclause 7.10.4 at the group communication session establishment step.

7.10.4 Video call connect and disconnect over MBMS

7.10.4.1 General

MBMS bearer can be used for MCVideo group calls. One MBMS bearer is not permanently associated to one specific group or group call. Before sending media packets of a group call over MBMS bearer, the MCVideo server shall send the association information between group call and the MBMS bearer. The group call setup procedure indicates the media stream or media streams within one MBMS bearer that is used for the specific MCVideo group call. When the group call over the MBMS bearer is finished, this temporary association information of an MCVideo group call to specific resources on a MBMS bearer is undone. The procedure in figure 7.10.4.2.1-1 requires that the group session is setup before the call start. This eliminates the need for the receiving clients to continuously use a unicast bearer. Prior to this the MBMS bearer is activated and announced to the MCVideo clients.

7.10.4.2 Procedure

7.10.4.2.1 Call connect over MBMS

In figure 7.10.4.2.1-1 the MCVideo client 1 is the client that initiate an MCVideo chat group call and also the transmitting client. MCVideo client 1 may, but does not have to be in an MBMS service area. The MCVideo client 2 and MCVideo client 3 represents MCVideo clients receiving the MCVideo call over an MBMS bearer. There may be other receiving clients both over unicast bearers and over this or other MBMS bearer(s), however they are not illustrated in this figure.

The same procedure as for chat group call can also be applied for pre-arranged calls.

Pre-conditions:

– All users participating in the MCVideo group call are already affiliated to the group.

– All participating users have joined the group session.

Figure 7.10.4.2.1-1: Chat group call connect on MBMS bearer

1. Activation and announcement of MBMS bearer availability.

NOTE 1: The procedure does not include the steps for MCVideo client location reporting, or for MBMS capability information exchange.

2. MCVideo client 1 initiate the MCVideo group call by sending an initial transmit media request over a unicast bearer to the MCVideo server (reference point MCVideo-4).

3. The MCVideo server will send a MapGroupToBearer message over a previously activated MBMS bearer to all users that will receive the call over an MBMS bearer. The MapGroupToBearer message includes association information between the group call and MBMS bearer. The MapGroupToBearer message includes MCVideo group ID and information about the media stream identifier or media stream identifiers of the activated MBMS bearer and may include the identifier (i.e. the TMGI) of the MBMS bearer broadcasting the call. The message is sent over reference point MCVideo-9.

NOTE 2: Step 3 can be deferred until step 5 and the MapGroupToBearer message can then be included in the transmission arbitration taken message.

4. The MCVideo server grants the right to transmit for MCVideo client 1 and by that sends a transmit media granted message to the MCVideo client 1. This message is sent over a unicast bearer (reference point MCVideo-4).

5. A media transmission notification message is sent from the MCVideo server to all receiving users. This message includes the MCVideo ID of the transmitting MCVideo client as well as the MCVideo group ID. The message is sent over a MBMS bearer to all users that have previously been setup to receive calls over the MBMS bearer. The message is sent over reference point MCVideo-9.

6. The users of MCVideo clients are informed about the details of video tranmission and the video transmitter.

7. The MCVideo clients may send a receive media request to the MCVideo server, to indicate the reception of media over the MBMS bearer.

8. MCVideo server accepts the media receive request and sends a receive media response message to MCVideo clients over a MBMS bearer by using reference point MCVideo-9.

NOTE 3: The receive media response can also be sent by unicast to the MCVideo clients that request to receive media over the MBMS bearer.

NOTE 4: Step 7 and 8 may be omitted when auto-receive (i.e. forced reception mode) transmission mode is used based on configurations (e.g. for emergency group calls, imminent peril calls etc) as described in Annex A.

9. The media is sent from MCVideo client 1 to the MCVideo server over unicast bearer and from the MCVideo server to the MCVideo client 2 and MCVideo client 3 over MBMS bearer.

NOTE 5: Additional transmission request messages in the same call will not trigger the MapGroupToBearer message to be sent.

7.10.4.2.2 Call disconnect over MBMS

Figure 7.10.4.2.2-1 shows the high level procedure where an UnmapGroupFromBearer message is sent by the MCVideo server to the MCVideo clients to indicate that the MCVideo group call is being dissociated from the MBMS bearer.

Figure 7.10.4.2.2-1: Chat group call disconnect on MBMS bearer

1. An MCVideo group call is ongoing; the media is broadcasted over MBMS bearer to MCVideo client 2 and MCVideo client 3.

2. MCVideo server has determined to disconnect the call over the MBMS bearer for the MCVideo clients

3. An UnmapGroupFromBearer message is sent by the MCVideo server to MCVideo client 2, MCVideo client 3 and possibly to MCVideo client 1 (if in MBMS coverage area) on MBMS bearer(s).

NOTE 1: The UnmapGroupFromBearer message can be sent as part of other messages.

NOTE 2: The UnmapGroupFromBearer message and the MapGroupToBearer message can be combined, to facilitate switching bearers in one signalling step, as necessary.

7.10.5 Switching from MBMS bearer to unicast bearer

The MCVideo service shall support the procedure for switching from MBMS bearer to unicast bearer as specified 3GPP TS 23.280 [6] with the following clarifications:

– The MC service client is the MCVideo client;

– The MC service server is the MCVideo server; and

– The MC service ID is the MCVideo ID.

The MCVideo service shall use the MCVideo-1, MCVideo-4, MCVideo‑7, MCVideo-8 and MCVideo‑9 reference points for this procedure.