4.3.6 The RRC state machine

23.1213GPPArchitectural requirements for Release 1999Release 1999TS

The RRC state machine is a description model of how the UE and the UTRAN co-operate regarding RRC functionality. The RRC state describes the state of the UE in the UTRAN. Here follows a brief description of the RRC state machine, for more information see [UMTS YY.01] and [UMTS YY.03].

NOTE: RRC idle mode and RRC connected mode refer to the UE idle mode and UE connected mode respectively in [UMTS YY.01] and [UMTS YY.03].

The RRC state machine exists as peer entities, one in the UE and one in UTRAN. Apart from transient situations and error cases they are synchronised. The figure below illustrates the main modes/states of the RRC state machine.

Figure 4.11: RRC modes, main RRC states and main mode/state transitions

RRC-Idle_mode:

In the Idle mode there is no connection established between UE and UTRAN. There is no signalling between UTRAN and the UE except for system information that is sent from UTRAN down link on a Broadcast channel to the UE. The UE can also receive paging messages with a CN identity on the PCH. There is no information on the UE stored in UTRAN in this state.

RRC-Connected_mode:

In the Connected mode the main states are Cell Connected state and URA connected state. In this mode there is one RNC that is acting as Serving RNC (SRNC), and an RRC connection is established between the UE and this SRNC.

– When the UE position is known on cell level, the UE is in the cell connected state. When in cell connected state, the RRC connection mobility is handled by handover procedures.

– When the UE position is known on URA level, the UE is in the URA connected state. The URA contains a set of cells. URA updating procedures provides the mobility functionality in this state. In URA connected state no dedicated radio resources are used.