Total Identifiers used by MME for a UE?

Question

MME has ownership of how many identifiers and which identifier is most important and used mostly in the real network?

Answer 1

As per my knowledge these are the following UE Indentifiers which MME may use:
IMSI, MME-UE-S1AP-ID, S-TMSI, GUTI, P-TMSI.

Comments

Could you please tell me about MME-UE-S1AP-ID in which procedure do we use this?

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Once the MME allocates mme-Ue-S1AP-Id to an UE, it uses MME-Ue-S1ap-Id to identify an UE for futher signalling messages until UE gets detached or UE enters into ECM-IDLE state.

I would like to described to little bit here. When an UE wants to move from RRC-IDLE to RRC-CONNECTED state, UE starts RRC Connection Setup Procedure. RRC Connection Setup Complete is the last message of RRC Connection Setup Procedure. RRC Connection Setup Complete carries "nas pdu" , which is sent to MME. eNodeB sends this "nas pdu" along with some other information to MME using a S1-AP message i.e.  Initial UE message. Initial UE message has only enb-Ue-S1ap-id to identify an UE at eNodeB but when MME receives Initial UE  message, it allocates mme-Ue-S1ap-Id to identify an UE uniquely.
If you see "Initial Context Setup Request" message then you would see both the identifiers (eNodeB-UE-S1ap-Id and mme-UE-S1ap-Id).

Hope I answered your query. Feel free to ask any further query if you have.