UE States and State Transitions
The 3GPP standard defines simplified states and state transitions for LTE UE. This simplification is relative to previous standards such as UTRAN and GSM. At any given time, a powered on LTE UE is either IDLE or CONNECTED. LTE-Advanced relies on the same state definitions, and the following descriptions apply for both LTE and LTE-Advanced.
This chapter is organized as follows. Section 11.1 provides an overview of the UE state definitions, and the transitions between the different states. Section 11.2 is dedicated to describing processes performed when a UE is in the IDLE state, including processes for PLMN selection, cell selection and reselection, location registration, and support for manual CSG ID selection. In Section 11.3, the procedures for acquiring system information that are required for cell or network selections are described. Section 11.4 goes over the procedures for establishing and control connections in LTE and LTE-Advanced. These procedures involve the random access mechanisms exercised to gain initial access to the network, in addition to dedicated signaling for connection establishment and re-establishment, connection reconfiguration, in addition to process engaged when a UE leaves the connected state. The final section in the chapter, Section 11.5, describes how the access stratum states described throughout are mapped to the NAS states.