Chapter 12 - Procedures

Abstract

This chapter introduces some of the procedures used in an Evolved Packet System (EPS). Attach is the first procedure the End-User Equipment (UE) executes after being switched on. The procedure is performed to make it possible to receive services from the network. An optimization in the SAE system is that the attach procedure also includes the establishment of a default EPS bearer ensuring that always-on IP connectivity for UE/users of the EPS is enabled. The detach procedure is used to remove bearers and clear states in the network when, for example, the UE is turned off. The detach procedure can also be used by the network to remove the bearers and states for a UE that has missed to perform TA update because it is out of coverage. Tracking Area update procedure is one of the mobility management procedures that are used to ensure that the MME knows in which TA, or set of TAs, the UE is currently located in. TA update is performed when the UE moves to a TA outside the list of TAs it was assigned in the previous TA update or attach procedure. TA update is also performed periodically even if the UE remains in the assigned TAs.