5G: What is the reason AMF and UE both maintain some context even been int RM-DEREGISTERED State ?

Question

I was comparing UE Context Release Cmd (defined in 36.413) with the NG-AP (38.413) UE Context Release Cmd. I couldn't realize the scenario in which only the AMF allocated UE NG-AP ID will be included in UE Cntxt Release Cmd. In LTE, both the S1-AP IDs were mandatory to send in UE Ctxt Rel Cmd from MME to eNodeB.
It would be helpful if someone can provide the reason.
Thanks in advance.

Answer 1

Even after execution of de-registration procedure, UE and AMF stores some part of context so that authentication procedure can be avoided for the subsequent registration.