- GUTI Reallocation procedure is used to allocate GUTI and optionally new TAI list to the UE.
- This procedure is always initiated by MME in EMM-REGISTERED state
- This procedure is performed in chipered mode, normally takes place in conjunction with other mobility management procedure.
- If UE lower layers indicate transmission failure of GUTI REALLOCATION COMPLETE message with TAI change and is not part of new TAI list UE should abort current procedure and starts TAU.
- IF lower layer failure detected at NW before T3450 timer expiry,NW should consider both old and new GUTI and old and new TAI list as valid.
- For paging first UE should try with S-TMSI from old GUTI and try in old and new TAI list, if response received from UE network should restart the GUTI reallocation procedure again
- In no response received network should use S-TMSI from new GUTI and page in new TAI list.
- If UE sends attach, detach or tracking area update request while on going GUTI procedure network should abort current GUTI procedure and proceed with specific EMM procedure.
Figure : GUTI Reallocation Procedure:
GUTI:
- GUTI size is 80 bits and is composed of Globally Unique MME Identity (GUMMEI) which is of 48 bits long and M-TMSI (Temporary Mobile Subscriber Identity)which of 32 bits long.
- GUMMEI : used to identify the MME which allocated this GUTI. Composed of PLMN (MMC MNC) code, MME Group Id and MME code