What happens when SRVCC fails at the NW side?
How UE is notified about it and the action it should take?
Notification Procedure (ESM Procedure)
The network can use the notification procedure to inform the UE about events which are relevant for the upper layer which is using an EPS bearer context or has requested a procedure transaction.
If the UE has indicated that it supports the notification procedure, the network may initiate the procedure at any time while a PDN connection exists or a procedure transaction is ongoing.
When the UE receives a NOTIFICATION message, the ESM protocol entity in the UE shall provide the notification indicator to the upper layer.
The notification indicator can have the following value:
#1: SRVCC handover cancelled, IMS session re-establishment required.
The following abnormal case can be identified:
a) Lower layer indication of non-delivered NAS PDU due to handover
If the NOTIFICATION message could not be delivered due to an intra MME handover, then upon successful completion of the intra MME handover the MME shall re-transmit the NOTIFICATION message. If a failure of the handover procedure is reported by the lower layer and the S1 signalling connection exists, the MME shall re-transmit the NOTIFICATION message.
How UE is notified about it and the action it should take?
Notification Procedure (ESM Procedure)
The network can use the notification procedure to inform the UE about events which are relevant for the upper layer which is using an EPS bearer context or has requested a procedure transaction.
If the UE has indicated that it supports the notification procedure, the network may initiate the procedure at any time while a PDN connection exists or a procedure transaction is ongoing.
When the UE receives a NOTIFICATION message, the ESM protocol entity in the UE shall provide the notification indicator to the upper layer.
The notification indicator can have the following value:
#1: SRVCC handover cancelled, IMS session re-establishment required.
The following abnormal case can be identified:
a) Lower layer indication of non-delivered NAS PDU due to handover
If the NOTIFICATION message could not be delivered due to an intra MME handover, then upon successful completion of the intra MME handover the MME shall re-transmit the NOTIFICATION message. If a failure of the handover procedure is reported by the lower layer and the S1 signalling connection exists, the MME shall re-transmit the NOTIFICATION message.
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