Why MME UE S1AP ID is needed ?

Question

Why cant we use IMSI for the same purpose?

Answer 1

IMSI is one of the confidential information which should not go outside from core network. An eNodeB can be shared by multiple operators so that it is not good to keep such type of information at eNodeB. Just to identify an UE at MME, eNodeb allocates eNodeB allocates enbUeS1apId and MME allocates mmeUeS1apId. These Ids are temporary and gets deleted once the UE detaches from the network or goes to idle mode.

Comments

Well explained ! +1

Answer 2

MME UE S1AP id is used to uniquely identify the UE in MME. It is assign by MME when MME sends first NAS msg to eNB after getting initial UE message.