Network-initiated Service Request Rejection Call Flow
During network-initiated service request, SMF handles the temporary reject for N1N2 response message from AMF as mentioned in 3GPP TS 23.502, section 4.2.3.3.

Step |
Description |
---|---|
1 |
On receiving a trigger for service request in UP IDLE session state, SMF initiates a N1N2 message towards the AMF as part of idle mode exit procedure. |
2 |
If UE registration procedure with new AMF is in progress, then AMF responds with temporary reject for N1N2 message with response code 409 and cause as TEMPORARY_REJECT_REGISTRATION_ONGOING or TEMPORARY_REJECT_HANDOVER_ONGOING SMF. |
3 |
On receiving the response, SMF starts a locally configured guard timer of 2 seconds. |
4 |
While the guard timer is running, SMF expects either a SM Context Update with AMF ID change or SM Context Update for handover. |
5 |
On receiving SM Context Update with AMF ID change, SMF:
|
6 |
On receiving SM Context Update for N2 handover, SMF:
|

Step |
Description |
---|---|
1 |
On receiving a trigger for service request in UP IDLE session state, SMF initiates a N1N2 message towards the AMF as part of idle mode exit procedure. |
2 |
If UE registration procedure with new AMF is in progress, then AMF responds with temporary reject for N1N2 message with response code 409 and cause as TEMPORARY_REJECT_REGISTRATION_ONGOING or TEMPORARY_REJECT_HANDOVER_ONGOING SMF. |
3 |
On receiving the response, SMF starts a locally configured guard timer of 2 seconds. |
4 |
Once the guard timer expires, SMF:
|