GUTI

在attach accept, TAU accept, Rau accept中帶給UE的。

1. RAT-related TMSI 
a. RAT-related TMSI 是採用ISR後來設置TIN
b. When the UE is camping on an E-UTRAN cell, the RAT-related TMSI is the GUTI; 
c. When it is camping on a GERAN or UTRAN cell, the RAT-related TMSI is the P-TMSI.

2. old GUTI / additional GUTI

The UE indicates also information elements "additional GUTI" or "additional P-TMSI" in the Attach Request, TAU or RAU Request. These information elements permit the new MME/SGSN to find the already existing UE contexts from the old MME or SGSN, when the "old GUTI" or "old P-TMSI" indicate values that are mapped from other identities.

If the UE is unknown in both the old MME/SGSN and new MME, the new MME sends an Identity Request to the UE to request the IMSI. The UE responds with Identity Response (IMSI).


在和新的MME通信過程中，如果手機使用了GUTI來標識自己，新的MME會通過GUTI獲得上次為手機服務的MME/SGSN的地址，並且向其發送Identification Request (old GUTI, complete Attach Request message)來請求IMSI。如果Identification Request被發送到老的MME或SGSN， 則他們分別通過NAS MAC和P-TMSI signature對請求進行驗證，如果通過驗證會返回Identification Response (IMSI, MM Context)。

Reference
http://blog.csdn.net/wangzhiyu1980/article/details/7750048
http://sridharbhaskaran.blogspot.tw/2010/05/additional-guti-and-additional-p-tmsi.html

3.