When S-TMSI or IMSI included in paging UE identity within paging message?

Question

It may be an easy question but still I have some doubt.
How RRC Connection setup procedure gets impacted with the presence of "S-TMSI" as an UE-Identity within the RRC Connection Request message ?
Note: RRC Connection request message can carry either 5 bytes long (S-TMSI) or 5 bytes long random value.

Answer 1

I was just thinking the scenario and sharing thoughts. Once the UE gets handed over from source enodeb to target enodeb with MME relocation, target MME shall send paging message to UE with IMSI since S-TMSI was allocated by source MME and will be invalid at target MME. S-TMSI is a combination or MMEC+ M-TMSI, reason being, I am thinking this may the scenario when MME sends paging message to UE with IMSI.

It is just my thought, there may be other scenarios as well in which MME prefer IMSI in paging message. Looking for others to respond.

Comments

thank you vikram

Answer 2

In normal scenario S-TMSI is used to page the UE?

when valid S-TMSI is not available due to a network failure then UE can be paged using IMSI.