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Content for  TS 23.280  Word version:  19.0.1

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10.7.3  Procedures for MBMS usagep. 136

10.7.3.1  Use of pre-established MBMS bearersp. 136

10.7.3.1.1  Generalp. 136
In this scenario, the MC service server pre-establishes MBMS bearer(s) in certain pre-configured areas before the initiation of the group communication session. When a user originates a request for a group communication session for one of these areas, the pre-established MBMS bearer(s) is used for the DL media transmission.
The following steps needs to be performed prior the start of the MC group communication session over pre-established MBMS bearer:
  • MBMS bearer(s) is Pre-established
  • Announce the pre-established MBMS bearer to the MC service clients
When these preparation steps have been done the MC group communication session using MBMS bearer can start.
Both the media packets as well as the application level control signalling (e.g. floor control messages) to the receiving MC service clients are sent on the MBMS bearer. Optionally a separate MBMS bearer could be used for the application level control messages, due to different bearer characteristic requirements.
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10.7.3.1.2  Procedurep. 136
The procedure Figure 10.7.3.1.2-1 shows only one of the receiving MC service clients using an MBMS bearer. There might also be MC service clients in the same MC group communication session that receive the communication on unicast bearers.
Pre-conditions:
  • The participating users are already affiliated.
Reproduction of 3GPP TS 23.280, Fig. 10.7.3.1.2-1: Use of pre-established MBMS bearers
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Step 1a.
The MC service server determines to activate MBMS bearer. The activation of the MBMS bearer is done on the MB2-C reference point and according to TS 23.468. This bearer will be used for the MC communication media.
Step 1b.
Optionally, the MC service server may also activate an MBMS bearer dedicated for application level control signalling. The activation of the MBMS bearer is done on MB2-C reference point and according to TS 23.468.
Step 2a.
The MC service server passes the MBMS bearer info for the service description associated with the pre-established MBMS bearer to the MC service client. The MC service client obtains the TMGI, identifying the MBMS bearer, from the service description.
Step 2b.
The MC service server may pass the MBMS bearer info for the service description associated with the pre-established floor control MBMS bearer to the MC service client. The MC service client obtains the TMGI, identifying the MBMS bearer, from the service description.
Step 3.
The MC service client stores the information associated with the TMGI(s). The MC service client uses the TMGI and other MBMS bearer related information to activate the monitoring of the MBMS bearer by the MC service UE.
4. The MC service client that enters or is in the service area of at least one announced TMGI indicates to the MC service server that the MC service client is able to receive media over MBMS, whereby the MC service server may decide to use the MBMS bearer instead of unicast bearer for MC communication sessions.
Step 5.
An MC service group communication session is established.
Step 6.
As the MC service server transmits the media over the MBMS bearer, the media packets are detected and delivered to the MC service client.
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10.7.3.2  Use of dynamic MBMS bearer establishmentp. 138

In this scenario depicted in Figure 10.7.3.2-1, the MC service server uses a unicast bearer for communication with the UE on the DL at the start of the group communication session. When the MC service server decides to use an MBMS bearer for the DL media transmission, the MC service server establishes an MBMS bearer using the procedures defined in TS 23.468. The MC service server provides MBMS service description information associated with MBMS bearer(s), obtained from the BM-SC, to the UE. The UE starts using the MBMS bearer(s) to receive DL media and stops using the unicast bearer for the DL media transmission.
Reproduction of 3GPP TS 23.280, Fig. 10.7.3.2-1: Use of dynamic MBMS bearer establishment
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Step 1.
An MC service group communication session is established.
Step 2.
The downlink data is sent by unicast delivery.
Step 3.
The MC service server establishes the MBMS bearer(s) for the group communication session according to the procedures defined in TS 23.468. Service description associated with the MBMS bearer(s) is returned from the BM-SC.
Step 4.
The MC service server provides service description information associated with the MBMS bearer to the UE. The MC service UE obtains the TMGI from the announcement message. This message may be sent on an application level control signalling bearer.
Step 5.
The MC service UE starts monitoring data over MBMS associated with the TMGI, while in the service area associated with the TMGI.
Step 6.
The MC service UE detects that it is able to receive data over MBMS associated with the TMGI.
Step 7.
The MC service client notifies the MC service server the MBMS listening status associated to the monitored TMGI, (e.g. that it is successfully receiving the TMGI). The MC service client may also notify the MBMS reception quality level of the TMGI. MC service server stops sending media data over unicast way to the MC service client.
Step 8.
An MC service group communication session via dynamic MBMS bearer(s) is established.
Step 9.
MC service server sends the downlink media for the group communication session over the MBMS.
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10.7.3.3  Switching from MBMS bearer to unicast bearerp. 139

Figure 10.7.3.3-1 shows the procedure for service continuity when a UE is about to move out of MBMS coverage by switching from MBMS bearer to unicast bearer.
Pre-conditions:
  • It is assumed that the MBMS bearer has been activated by MC service server for downlink delivery.
Reproduction of 3GPP TS 23.280, Fig. 10.7.3.3-1: Switching from MBMS delivery to unicast delivery
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Step 1.
The MC service UE detects that it suffers from bad MBMS bearer condition for the corresponding MBMS service. The method to detect is implementation specific.
Step 2.
The MC service client notifies the MC service server that it suffers from bad MBMS bearer condition for the corresponding MBMS service by sending the MBMS listening status report.
Step 3.
The MC service server sends the downlink data by unicast delivery to the MC service client.
Step 4.
During the switching, the MC service client simultaneously receives downlink data through both unicast bearer and MBMS bearer. If there is no downlink data to the MC service client, this step can be skipped.
Step 5.
The MC service client ceases to receive the downlink data through MBMS bearer but continues receiving data through unicast bearer.
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