N1N2 Message Transfer Request Call Flow
This section describes the N1N2 Message Transfer Request call flow.

Step |
Description |
---|---|
1 |
The peer node sends an N1N2MessageTransfer Request Call Flow message to the AMF. |
2 |
AMF checks if the message is acceptable. If there’s an exception, the AMF rejects the message with an appropriate cause code. |
3 |
If the UE is in ECM_CONNECTED state, AMF forwards the message to the UE or gNB. The N2 message received from the peer node determines the N2 message type. If there’s a N1 message, it’s sent as a payload to the N2 message. AMF then responds with a 200 OK to the peer node. |
4 |
If the UE is in ECM_IDLE state and the Asynchronous Transfer flag is set, AMF stores the message in a known location in CDL. AMF adds the location header to the response and a 202 response is sent with WAITING_FOR_ASYNCHRONOUS_TRANSFER as a diagnostic. The saved message is sent to the UE as the UE transitions to ECM_CONNECTED. The AMF doesn’t page the UE in this case. |
5 |
If the UE is in ECM_IDLE state and the SkipInd flag is set in the received N1N2TransferReq message, AMF skips sending the N1 message to UE. AMF sends a 200 OK response with N1_MSG_NOT_TRANSFERRED as a diagnostic. The message isn’t sent to the UE as the UE transitions to ECM_CONNECTED and paging isn’t done in this scenario. |
6 |
If the UE is in ECM_IDLE and the Asynchronous Transfer flag isn’t set, AMF stores the message in a known location. AMF adds the location header to the response and a 202 response is sent with ATTEMPTING_TO_REACH_UE as a diagnostic. The saved message is sent to the UE as the UE transitions to ECM_CONNECTED. If paging fails, AMF sends a Failure Notification to the peer node. |