Tracking Area is used to manage a LTE network in a large geographical region. A large geographical region can be divided into multiple tracking areas and each tracking area may have hundred of cells. Size of a tracking area depends on network deployment. Tracking area is one of parameter which indicates UE location along with cell global identity. When an UE goes to RRC-IDLE or ECM-IDLE mode, MME does paging for UE if any downlink data receives. In this situation, UE location is identified at tracking area level and MME sends paging message to all eNodeB's within the tracking area.
UE can perform tracking area update either periodic or a-periodic. Periodic tracking area update procedure is controlled in UE by timer T3412. When timer T3412 expires, the periodic tracking area update procedure is started. Another one is known as a-periodic, I mean to say when an UE enters into a tracking area that is not in the list of tracking areas that the UE previously registered in the MME, It starts tracking area update procedure. Tracing area update procedure is also done in case of MME load balancing.