What are all the possible reasons for which UE does not send Uplink PDN Connectivity Request?

RAN
1

Hi All.

What are all the possible reasons for which UE does not send Uplink PDN Connectivity Request?

For IMS I mean. So network will configure the DRB for QCI5 default bearer.

The UE comes back from 3G to 4G but does not establish QCI% bearer hence no VoLTE , all calls are CSFB.

QCI5.

2
  1. UE becoming Voice centric with CS voice preferred.
  2. Check TAU Accept if IMS vops not available.
  3. Previous IMS Reg request Rejected with some timeout.