TAU
Tracking Area Update
The LTE UE detects a change to a new TA (Tracking Area) by decoding the TAI (Tracking Area Identity) broadcast on the serving cell that it has just selected. This is done by comparing this value with the list of TAI that the UE has registered in the network. The TAU procedure is performed due to a variety of reasons, such as TA updating, combined TA/LA updating, combined TA/LA updating with IMSI attach and periodic updating.