When the UDM stores the associated Access Type (e.g. 3GPP) together with the serving AMF as indicated in step 14a, it will cause the UDM to initiate a Nudm_UECM_DeregistrationNotification (see clause 126.96.36.199.2
) to the old AMF corresponding to the same (e.g. 3GPP) access, if one exists. The old AMF removes the UE context of the UE. If the serving NF removal reason indicated by the UDM is Initial Registration, then, as described in clause 188.8.131.52.2
, the old AMF invokes the Nsmf_PDUSession_ReleaseSMContext (SUPI
, PDU Session ID) service operation towards all the associated SMF(s) of the UE to notify that the UE is deregistered from old AMF. The SMF(s) shall release the PDU Session on getting this notification.