LTE, LTE-Advanced and WiMAX: Towards IMT-Advanced Networks

Connection Establishment and Control

Prior to describing RRC procedures for connection establishment and, in general, control, a description of Signaling Radio Bearers (SRB) is required. SRBs are RBs that are used solely for the transmission of RRC and NAS messages. SRB0 is used for RRC messaging using the CCCH logical channel, which is the channel used for UEs having no RRC connection with the network. On the other hand, SRB1 utilizes DCCH and is used for RRC messages (including piggybacked NAS messages), as well as NAS messages transmitted prior to establishing SRB2. Note that the establishment of an RRC connection involves the establishment of an SRB1. SRB2 also utilizes DCCH and is used for NAS messages. SRB2 has a lower priority than SRB1, and is always configured after security activation.

Random Access Procedure

Connection establishment begins with a procedure for random access through which the user is scheduled a transmission to initiate connection setup. There are other instances where the random access procedure may be required. These include RRC connection re-establishing, handover, upon data arrival in the uplink or downlink while the UE is not synchronized or allocated resources, and for positioning while in the CONNECTED state.

There are two types of random access procedure: contention based, and non-contention based. The non-contention based procedure is utilized when it is the network that is trying to establish the connection. The contention based procedure is ...