Download

13.4 UTRAN AIR INTERFACE 449Figure 13.4-7. RLC PDU format for unacknowledged mode.13.4.6 Radio Resource Control (RRC) SublayerThe RRC sublayer is present only in the control plane, which is another way ofsaying that it only handles signaling traffic. User traffic does not go through theRLC sublayer (Fig. 13.4-2) [45]. The RRC interfaces with the RLC on the lowerboundary and with higher-layer signaling on the other boundary. The main functionsof RRC are:. Management of signaling radio bearers. Management of connections between RRC entities in MS and BS. Control of QoSRRC connections are bidirectional and a MS may have only one RRC connectionestablished at a time.The RRC sublayer provides local signaling connectivity between peer entitiesin the MS and the BS and manages the radio access portion of the network. Onceestablished, RRC connections allow higher-layer signaling functions to exchangemessages for call management and mobility management, functions that connecta MS directly with the core network (Fig. 13.4-1). Call management and mobilitymanagement messages are transferred transparently between the MS and CN, encapsulatedinto RRC Direct Transfer messages.RRC supports two modes of operation:1. Idle mode2. Connected modeIn idle mode the MS is activated but not involved in a user-to-user connection.The MS is identified by global (non-access-network) identifiers such as IMSI orTMSI (Section 12.7.4).In connected mode the MS is involved in a user-to-user connection. The MS isidentified by a local identifier, called the UMTS radio network temporary identifier(U-RNTI or simply RNTI). The RNTI does not have any significance outside theradio access network.