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Content for  TS 23.289  Word version:  19.0.0

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7.3.3.9  MC service inter-system switching between 5G and LTEp. 83

7.3.3.9.1  Generalp. 83
When working in transport only mode, the MC service server guides the MC service clients throughout the MC media transmission for switching between the LTE and 5G systems. For this purpose, the location management client sends location related information to the location management server, similar to the one defined in TS 23.280, which is triggered due to its location change - in this case due to Radio Access Technology (RAT) change, to inform the server hence the latter provides guidance related to how to receive the MC services after the location update.
The procedures cover both the deployment scenarios with/without MBSF/MBSTF. The procedures specify four inter-system switching related scenarios as follows:
  1. Inter-system switching from 5G MBS session to LTE eMBMS bearer, as in clause 7.3.3.9.2
  2. Inter-system switching from 5G MBS session to LTE unicast bearer, as in clause 7.3.3.9.3
  3. Inter-system switching from LTE eMBMS to 5G MBS session, as in clause 7.3.3.9.4
  4. Inter-system switching from LTE eMBMS to 5G unicast PDU session, as in clause 7.3.3.9.5
In all the inter-system switching related scenario described in clause 7.3.3.9.2, clause 7.3.3.9.3, clause 7.3.3.9.4 and clause 7.3.3.9.5, the functional entity that resides in 5GS may be NEF, or MBSF, or MB-SMF for session creation and together with PCF or PCC related interaction.
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7.3.3.9.2  Inter-system switching from 5G MBS session to LTE eMBMS bearerp. 83
The procedure provided in Figure 7.3.3.9.2-1 describes how the MC service server handles inter-system switching when the MC service UE switches from 5G to LTE network, where the MC service server is able to provide the MC services to the clients over eMBMS bearer(s).
Pre-conditions:
  • MC service clients are attached to the 5GS, registered and affiliated to the same MC service group X.
  • The MC services can be provided via both 5GS and EPS.
  • The MC service client(s) is within the eMBMS service area.
  • It is assumed that the MC service client(s) has not received the eMBMS bearer announcement while camping in 5GS.
Copy of original 3GPP image for 3GPP TS 23.289, Fig. 7.3.3.9.2-1: Inter-system switching from 5G MBS session to LTE eMBMS bearer.
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Step 1.
An MC service group communication takes place, and the MC media is delivered over 5G MBS session (either broadcast or multicast session mode), which is associated to the MC service group X.
Step 2.
The MC service UE performs handover to EPS.
Step 3.
Location information handling can be based on location reports provided by the MC service client, where the MC service UE`s location information is provided via the location management client, triggered by RAT change, to the location management server, where the latter provides the location information to the MC service server.
Also, location information handling can be based on notifications provided from the network to the MC service server related to 5GS supporting EPS interworking, as specified in TS 23.501, TS 23.502, and TS 23.503 and described in clause 7.4.3. For that, the MC service server can subscribe to receive notifications of specific events from the network. For instance, the MC service server can subscribe to PCF related notifications (via N5 or Rx) for specific events, e.g., access network information notification and change of access type. Also, when SCEF+NEF is deployed, the MC service server can subscribe to SCEF+NEF related notifications for specific events, e.g., core network (CN) type change.
Step 4.
The MC service server analyses the location information and decides how to serve the client. If the MC service server decides to serve the client via eMBMS bearer, it may send an eMBMS bearer announcement as described in TS 23.280. This step is optional as the bearer announcement related information could be sent in advance (implementation specific).
Step 5.
If not already available, the MC service client stores the announced TMGI(s), service area, and any relevant information to the eMBMS, which is delivered via the bearer announcement. As a result, the MC service client starts monitoring the bearer.
Step 6.
The MC service client sends an eMBMS listening status report to inform the server of its ability of receiving MC media over the specified bearer.
Step 7.
The MC server sends the necessary information related to receiving the MC media in the form of the MapGroupToBearer.
Step 8.
The MC service group communication takes place over EPS, and the MC media is transmitted over an eMBMS bearer.
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7.3.3.9.3  Inter-system switching from 5G MBS session to LTE unicast bearerp. 85
The procedure provided in Figure 7.3.3.9.3-1 describes how the MC service server handles inter-system switching when the MC service UE switches from 5G to LTE network, where the MC service server is unable to provide the MC services to the client over eMBMS bearer.
Pre-conditions:
  • MC service clients are attached to the 5GS, registered and affiliated to the same MC service group X.
  • The MC services can be provided via both 5GS and EPS.
Copy of original 3GPP image for 3GPP TS 23.289, Fig. 7.3.3.9.3-1: Inter-system switching from 5G MBS session to LTE unicast bearer.
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Step 1.
An MC service group communication takes place, and the MC media is delivered over 5G MBS session (either broadcast or multicast session mode), which is associated to the MC service group X.
Step 2.
The MC service UE performs handover to EPS.
Step 3.
Location information handling can be based on location reports provided by the MC service client, where the MC service UE`s location information is provided via the location management client, triggered by RAT change, to the location management server, where the latter provides the location information to the MC service server.
Also, location information handling can be based on notifications provided from the network to the MC service server related to 5GS supporting EPS interworking, as specified in TS 23.501, TS 23.502, and TS 23.503 and described in clause 7.4.3. For that, the MC service server can subscribe to receive notifications of specific events from the network. For instance, the MC service server can subscribe to PCF related notifications (via N5 or Rx) for specific events, e.g. access network information notification and change of access type. Also, when SCEF+NEF is deployed, the MC service server can subscribe to SCEF+NEF related notifications for specific events, e.g. core network (CN) type change.
Step 4.
The MC service server may interact with the EPC for providing the required media resources over the unicast bearer, if not already allocated.
Step 5.
The MC service group communication takes place over EPS, and the MC media is transmitted over a unicast bearer.
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7.3.3.9.4  Inter-system switching from LTE eMBMS to 5G MBS sessionp. 87
The procedure provided in Figure 7.3.3.9.4-1 describes how the MC service server handles inter-system switching when the MC service UE switches from LTE network to 5G, where the MC service server is able to provide the MC services to the client over 5G MBS sessions (either broadcast or multicast).
Pre-conditions:
  • MC service clients are attached to the EPC and affiliated to the same MC service group X.
  • The MC services can be provided via both 5GS and EPS.
  • The MC service client(s) is within the service area (if the session is limited to an area), where the MBS session is configured.
  • It is assumed that the MC service client(s) has not received the 5G MBS session announcement while camping in EPS.
Copy of original 3GPP image for 3GPP TS 23.289, Fig. 7.3.3.9.4-1: Inter-system switching from LTE eMBMS bearer to 5G MBS sessions (either broadcast or multicast).
Up
Step 1.
An MC service group communication takes place, and the MC media is delivered over eMBMS bearer, which is associated to the MC service group X.
Step 2.
The MC service UE performs handover to 5GS.
Step 3.
Location information handling can be based on location reports provided by the MC service client, where the MC service UE`s location information is provided via the location management client, triggered by RAT change, to the location management server, where the latter provides the location information to the MC service server.
Also, location information handling can be based on notifications provided from the network to the MC service server related to 5GS supporting EPS interworking, as specified in TS 23.501, TS 23.502, and TS 23.503 and described in clause 7.4.3. For that, the MC service server can subscribe to receive notifications of specific events from the network. For instance, the MC service server can subscribe to PCF related notifications (via N5 or Rx) for specific events, e.g., access network information notification and change of access type. Also, when SCEF+NEF is deployed, the MC service server can subscribe to SCEF+NEF related notifications for specific events, e.g., core network (CN) type change.
Step 4.
The MC service server analyses the location information and decides how to serve the client. If the MC service server decides to serve the client via 5G MBS session, it may send an MBS session announcement indicating information among others the session mode to serve the MC service client and the corresponding MBS session ID. This step is optional as the session announcement related information could be sent in advance (implementation specific).
Step 5.
The MC service UE acts according to the MBS session mode provided to receive the DL media.
Step 5a.
In case of multicast MBS sessions, the MC service UE performs a UE session join towards the 5GC indicating the MBS session ID to join. It may as well send a UE session join acknowledgement to the MC service server.
Step 5b.
In case of broadcast MBS sessions, the MC service UE starts monitoring the broadcast MBS session.
Step 6.
The MC service client sends an MBS listening status report to the server indicating its ability to receive media over the indicated MBS session.
Step 7.
The MC service server sends a MapGroupToSessionStream over the MBS session providing the required stream information to receive the media related to the group communication.
Step 8.
The MC service client processes the received information related to the MC media over the MBS session.
Step 9.
The MC service group communication takes place over 5GS, and the MC media is delivered over the broadcast or multicast MBS session.
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7.3.3.9.5  Inter-system switching from LTE eMBMS to 5G unicast PDU sessionp. 88
The procedure provided in Figure 7.3.3.9.5-1 describes how the MC service server handles inter-system switching when the MC service UE switches from LTE network to 5G, where the MC service server is able to provide the MC services to the client over 5G MBS sessions (either broadcast or multicast).
Pre-conditions:
  • MC service clients are attached to the EPC and affiliated to the same MC service group X.
  • The MC services can be provided via both 5GS and EPS.
Copy of original 3GPP image for 3GPP TS 23.289, Fig. 7.3.3.9.5-1: Inter-system switching from LTE eMBMS bearer to 5G unicast PDU session.
Up
Step 1.
An MC service group communication takes place, and the MC media is delivered over eMBMS bearer, which is associated to the MC service group X.
Step 2.
The MC service UE performs handover to 5GS.
Step 3.
Location information handling can be based on location reports provided by the MC service client, where the MC service UE`s location information is provided via the location management client, triggered by RAT change, to the location management server, where the latter provides the location information to the MC service server.
Also, location information handling can be based on notifications provided from the network to the MC service server related to 5GS supporting EPS interworking, as specified in TS 23.501, TS 23.502, and TS 23.503 and described in clause 7.4.3. For that, the MC service server can subscribe to receive notifications of specific events from the network. For instance, the MC service server can subscribe to PCF related notifications (via N5 or Rx) for specific events, e.g. access network information notification and change of access type. Also, when SCEF+NEF is deployed, the MC service server can subscribe to SCEF+NEF related notifications for specific events, e.g. core network (CN) type change.
Step 4.
The MC service server may interact with the 5GC to request media resources (if not already allocated) with specific requirements over unicast PDU session, as it is able to serve the MC service client via unicast PDU session, as described in clause 7.2.
Step 5.
The MC service group communication takes place over 5GS, and the MC media is delivered over unicast PDU session.
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