作用：The purpose of the GUTI is to provide an unambiguous identification of the UE that does not reveal the UE or the user's permanent identity in the Evolved Packet System (EPS).
分配：It also allows the identification of the MME and network. It can be used by the network and the UE to establish the UE's identity during signalling between them in the EPS. See 3GPP TS 23.401 [72].
The GUTI has two main components:
-one that uniquely identifies the MME which allocated the GUTI; and
-one that uniquely identifies the UE within the MME that allocated the GUTI.
Within the MME, the mobile shall be identified by the M-TMSI.
The Globally Unique MME Identifier (GUMMEI) shall be constructed from the MCC, MNC and MME Identifier (MMEI).
The MMEI shall be constructed from an MME Group ID (MMEGI) and an MME Code (MMEC).
The GUTI shall be constructed from the GUMMEI and the M-TMSI.
For paging purposes, the mobile is paged with the S-TMSI. The S-TMSI shall be constructed from the MMEC and the M-TMSI.
The operator shall need to ensure that the MMEC is unique within the MME pool area and, if overlapping pool areas are in use, unique within the area of overlapping MME pools.
The GUTI shall be used to support subscriber identity confidentiality, and, in the shortened S-TMSI form, to enable more efficient radio signalling procedures (e.g. paging and Service Request).
定義：The format and size of the GUTI is therefore the following:
<GUTI> = <GUMMEI><M-TMSI>,
where <GUMMEI> = <MCC><MNC><MME Identifier>
and <MME Identifier> = <MME Group ID><MME Code>
MCC and MNC shall have the same field size as in earlier 3GPP systems.
M-TMSI shall be of 32 bits length.
MME Group ID shall be of 16 bits length.
MME Code shall be of 8 bits length.
好好讀讀這段，你要的信息都有。
attach accept中網(wǎng)絡(luò)側(cè)會維護(hù)GUTI值，GUTI可能會變化。