When M-TMSI is generated and allocated to the UE by MME during TAU procedure?

Question

I would like to know when M-TMSI is generated and allocated to the UE by MME during TAU procedure, and which message is concerned.

Answer 1

As per my knowledge, when MME would not be able to find UE context based on GUTI or M-TMSI provided by UE, it will generate new GUTI or M-TMSI for the UE and send it back to UE using EMM message.

Sometimes, when TAU is received by MME which is different from the serving one. In that case, new MME fetches UE's information from old MME and will proceed with TAU procedure.

Comments

Hi, thank you for your answer.
I would like to confirm the follows:
1. what the EMM message can send back GUTI or M-TMSI to UE?
    TAU accept, GUTI reallocation command, or anything else?
2. in case of TAU, new MME can receive a UE Context by using Context Request / Response.  Is the message what you indicate Context Response?

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Please find answers for your queries as follows:
1. TAU accept carries new GUTI and TMSI which is allocated by new MME.
     new MME can't use old GUTI or M-TMSI since these IEs consist of MMEC as well and each MME has unique code with the MME group.

2. Yes, S10 interface messages Identification Request/Response messages shall be used to fetch necessary information like IMSI, MM Context etc. For details please go through 3GPP 29.274 specification.