The MME does not
perform GUTI Reallocation if the subscriber is marked for offload or if the
subscriber is executing an outbound handover procedure.
reallocation retries for UE's which do not adhere to specifications is limited
by the MME. MME detaches such UEs after "10" consecutive failure attempts of
GUTI Reallocation. This behavior and number of consecutive failures to trigger
detach is not configurable.
configured to trigger authentication/GUTI reallocation requires the new session
setup message (NAS Attach/TAU) to be processed by the Session Manager instance
which has the corresponding MME DB for the subscriber. If the MME DB is not
triggers will not work. For example, if the mobile identifier in the NAS
Attach/TAU message is a foreign GUTI and additional GUTI is not present, the
MME does not trigger authentication/GUTI reallocation for the subscriber based
Reallocated GUTI is
not sent in TAU accept for TAU with type TA Update. In this scenario, once the
frequency criteria for TAU is met, GUTI reallocation is performed on receiving
the next periodic TAU or Service request. This to prevent the case where, TAU
complete for an TAU accept with Reallocated GUTI is not received by MME.
Wherein upon receiving a paging trigger, MME needs to page the UE in both the
TAI lists (before and after TAU) with both the GUTI (previous and reallocated).
In the case of SGSN , paging message is sent to the RNC with acknowledged PTMSI
and unacknowledged (reallocated) PTMSI. However paging is sent only for the
current RAI. Similarly in the case of MME, MME has to send paging message to
the eNodeB's with acknowledged GUTI and unacknowledged GUTI (reallocated). But
paging needs to be sent in both current TAI list and previous TAI list.