Content for  TS 23.434  Word version:  19.3.0

The VAL server delivers the VAL data to the VAL UE(s) without being aware of the mobility of the VAL UE with the assistance and guidance of the NRM server. When working in transport only mode, the NRM server guides the NRM clients throughout the VAL data transmission for switching between the LTE and 5G systems. For this purpose, the location management client may send location related information to the location management server, similar to the one defined in clause 9, which is triggered due to its location change - in this case due to Radio Access Technology (RAT) change, to inform the NRM server hence the latter provides guidance related to how to receive the VAL data 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 14.3.4A.10.2
2. Inter-system switching from 5G MBS session to LTE unicast bearer, as in clause 14.3.4A.10.3
3. Inter-system switching from LTE eMBMS to 5G MBS session, as in clause 14.3.4A.10.4
4. Inter-system switching from LTE eMBMS to 5G unicast PDU session, as in clause 14.3.4A.10.5

In all the inter-system switching related scenario described in clause 14.3.4A.10.2, clause 14.3.4A.10.3, clause 14.3.4A.10.4 and clause 14.3.4A.10.5, 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.

The procedure provided in Figure 14.3.4A.10.2-1 describes how the NRM server handles inter-system switching when the VAL UE switches from 5G to LTE network, where the NRM server is able to provide the VAL data to the clients over eMBMS bearer(s). Pre-conditions:

• NRM clients are attached to the 5GS, registered.
• The VAL service can be provided via both 5GS and EPS.
• The NRM client(s) is within the eMBMS service area.
• It is assumed that the NRM client(s) has not received the eMBMS bearer announcement while camping in 5GS.

The procedure provided in Figure 14.3.4A.10.3-1 describes how the NRM server handles inter-system switching when the VAL UE switches from 5G to LTE network, where the VAL server is unable to provide the VAL services to the VAL UE over eMBMS bearer. Pre-conditions:

• NRM clients are attached to the 5GS, registered and affiliated to the same VAL group X.
• The VAL services can be provided via both 5GS and EPS.

The procedure provided in Figure 14.3.4A.10.4-1 describes how the NRM server handles inter-system switching when the VAL UE switches from LTE network to 5G, where the NRM server is able to provide the VAL services to the client over 5G MBS sessions (either broadcast or multicast). Pre-conditions:

• NRM clients are attached to the EPC.
• The VAL services can be provided via both 5GS and EPS.
• The NRM 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 NRM client(s) has not received the 5G MBS session announcement while camping in EPS.

The procedure provided in Figure 14.3.4A.10.5-1 describes how the NRM server handles inter-system switching when the VAL UE switches from LTE network to 5G, where the NRM server is able to provide the VAL services to the client over 5G MBS sessions (either broadcast or multicast). Pre-conditions:

• NRM clients are attached to the EPC and affiliated to the same VAL group X.
• The VAL services can be provided via both 5GS and EPS.