5.23 Supporting for Asynchronous Type Communication

23.5013GPPRelease 18System architecture for the 5G System (5GS)TS

Asynchronous type communication (ATC) enables 5GC to delay synchronizing UE context with the UE, so as to achieve an efficient signalling overhead and increase system capacity. The support of ATC is optional for the AMF.

5GC supports asynchronous type communication with the following functionality:

– Capability to store the UE context based on the received message, and synchronize the UE context with the involved network functions or UE later;

For network function (e.g. PCF, UDM, etc.) triggered signalling procedure (e.g. network triggered Service Request procedure, network triggered PDU Session Modification procedure, etc.), if the UE CM state in the AMF is CM-IDLE state and the requesting network function indicates to the AMF the ATC is allowed for the signalling, if the AMF supports the ATC feature, the AMF may update and store the UE context based on the received message without paging UE immediately. When the UE CM state in the AMF enters CM-CONNECTED state, the AMF forwards N1 and N2 message to synchronize the UE context with the (R)AN and/or the UE.

If the originating NF does not require immediate delivery, it may indicate that the AMF is allowed to use ATC.

NOTE: Pre-Rel-17 AMF implementation cannot decode the indication that ATC is allowed.