10.3. RRC Overview

The RRC layer takes care of RRC connection management, radio bearer control, mobility functions, and UE measurement reporting and control. It is also responsible for broadcasting system information and paging. In this section, we discuss the two RRC states in LTE and the functions provided by the RRC protocol.

10.3.1. RRC States

Compared to UMTS, which has four RRC states, LTE has only two states: RRC_IDLE and RRC_CONNECTED, as depicted in Figure 10.13. This simplifies the RRC state machine handling and the radio resource management, which controls the RRC state. A UE is in the RRC_CONNECTED state when an RRC connection has been established; otherwise, the UE is in the RRC_IDLE state.