5.19.7.1 General

NAS level congestion control may be applied in general (i.e. for all NAS messages), per DNN, per S-NSSAI, per DNN and S-NSSAI, or for a specific group of UEs.

NAS level congestion control is achieved by providing the UE a back-off time. To avoid that large amounts of UEs initiate deferred requests (almost) simultaneously, the 5GC should select each back-off time value so that the deferred requests are not synchronized. When the UE receives a back-off time, the UE shall not initiate any NAS signalling with regards to the applied congestion control until the back-off timer expires or the UE receives a mobile terminated request from the network, or the UE initiates signalling for emergency services or high priority access.

AMFs and SMFs may apply NAS level congestion control, but should not apply NAS level congestion control for procedures not subject to congestion control.