The Globally Unique Temporary UE Identity (GUTI) provides an unambiguous identification of the UE that does not reveal the UE or the user's permanent identity in the EPS.
The GUTI also allows the identification of the MME and the network. It can be used by the network and the UE to establish the UE's identity during signalling between them in the EPS. The GUTI has two main components as explained below:
- one that uniquely identifies the MME which allocated the GUTI (GUMMEI)
- one that uniquely identifies the UE within the MME that allocated the GUTI (M-TMSI)
The MME allocates GUTI by initiating GUTI reallocation procedure or it can also be implicitly reallocated during attach or tracking area updating procedures. Normally, the GUTI reallocation will take place in conjunction with another mobility management procedure, e.g. as part of tracking area update.
Section 5.4.1 of 3gpp TS 24.301 (NAS Protocol) has defined in each details.