ane Transport Transport Network ALCAP Network User Plane User Plane Signalling Signalling Bearer Bearer Bearer Physical Layer, Figure 7.3(b) General protocol structure for UTRAN RANAP (radio-access network application protocol) is the signalling protocol defined between the RAN and CN. The main function of RANAP is to control the resources on the I interface, providing both control and dedicated control services. RNSAP (radio network sub-system application protocol) provides the signalling on the Iur interface. As the Iur interface is present between the two RNCs (one is SRNC and the other is DRNC), it is managed by these two RNCs. RNSAP is responsible for management of bearer signalling on the Iur interface apart from the transport and traffic management functions. NBAP (node B application protocol) maintains the control plane signalling on the Iub interface. This protocol is responsible for communications between the node B (WCDMA base station) and UE. ALCAP (access link control application part) is required for setting up of the data bearer and signalling in the transport network control plane. The presence of ALCAP is necessary as the user plane and the control plane can be separated and independent from each other. ALCAP may or may not exist depending upon the type of data bearer. 7.2.3 Channel Configuration in WCDMA radio network As mentioned above, the MAC layer is responsible for mapping the logical channels on to the transport channels. It provides the data transfer services on the logical channels. As usual, logical channels are composed of control and traffic channels. These are again subdivided into common and dedicated channels. These channels along with their functions are noted in Table 7.1. 3G RADIO NETWORK PLANNING AND OPTIMISATION Table 7.1 Logical channels in a WCDMA radio network Channel Abbreviation Function/application Broadcast common control Transmits the system control channel information Common control channel Used (usually by the UE) for (UL/DL) transmitting information related to contr