Collision Case

AMF informs SMF about HO procedure by rejecting the N1N2 Transfer Request with temporary reject cause. Also any other procedure can pre-empt the UE synchronization procedure while it is awaiting N1 update from the UE.

Collision Case
Collision Case

Step

Description

1

If N1N2 Transfer Failure with cause as Temporary Reject Handover Ongoing is received, SMF awaits HO procedure to pre-empt PDU UE Sync Procedure.

2

While awaiting N1 Update or handover from UE, if any procedure (including handover) is triggered then:

  • If suspended by the handover procedure, it starts the N1N2 retry timer.

  • If aborted by PDU release or PDU setup procedure, it cleans up all the timers and aborts the N1N2 retry.

3

In case UE sync procedure is suspended by handover then on expiry of N1N2 Retry Timer, UE sync resumes after handover is processed.

4

On resuming if the UE sync procedure finds that the RAT has changed then it aborts the procedure and stop any timers.

5

On resuming the procedure in the same RAT the UE sync procedure reinitiates N11N1N2Transfer request message.