ing the slow associated control channels (SAACH), or by using the main channel itself wherein the signalling channel is sent instead of sending the data - this is known as fast associated control channel (FAACH) signalling. SAACH signalling is 'slow' and hence carries non-urgent messages, such as information containing handover measurement data. FAACH signalling carries information that is more urgent, such as decisions leading to handover of the mobile. Signalling is also required at the air-interface for sending information about the mobile itself even when it is not on a call. Thus, signalling can be in the dedicated phase (i.e. when TCHs have been allocated to the mobile) and in the non-dedicated or idle mode when the mobile is not on a call but is camped on the network. RADIO NETWORK PLANNING AND OPTIMISATION When the mobile firsts tries to get connected to the network, it requires the help of two channels: the frequency correction channel (FCCH) and the synchronisation channel (SCH). These channels help the mobile to get synchronised and connected to the network. Each mobile, once connected, keeps on receiving information from the base station, and this is done through the broadcast channel (BCCH). Once a call is initiated, the paging channel (PCH) helps in transfer of information indicating that a dedicated channel will be allocated to the mobile. This allocation information comes via the allocation grant channel (AGH). If the mobile needs to send information to the base station, the request is made through the random access channel (RACH). All these channels except RACH are downlink channels. The above-mentioned channels are logical channels. There are three kinds of physical channel also: the traffic channels for full-rate, half-rate and one-eighth rate (also known as TCH/F, TCH/H and TCH/8 respectively). TCH/F transmits the speech code at 13 kbps; TCH/H transmits speech code at 7 kbps. Although TCH/8 is a traffic channel, its rate is very low at almost one-eighth that of the TCH/F; thus its usage has be