As you know, network uses S-TMSI (MMEC+M-TMSI) as UE identity in paging.
Considering the fact that M-TMSI is unique within an MME, why can’t the paging identity be M-TMSI? What benefit are we adding by including the MMEC too to the M-TMSI here?
to ensure that the MMEC is unique within the MME pool area and, if overlapping pool areas are in use, unique within the area of overlapping MME pools.
The S-TMSI is used to protect the subscribers IMSI during NAS interaction as well as identifying the MME (Mobility Management Entity) or MME pool that is responsible for the UE. The S-TMSI is constructed from the MMEC (MME Code) and the M-TMSI.