s and sub-multiplexers are used between the BSC and the MSC. Although they are present in the BSS system as shown in Figure 3.1, physically they may be situated at the MSC location. The TCSM is capable of two functions: transcoding of speech signals and sub- multiplexing of PCM signals. The trancoder does the speech coding in the downlink direc- tion, which is decoded in the MS, and it decodes the speech signal in the uplink direction. Sub-multiplexers are located at the same place as the transcoders and are responsible for multiplexing of the PCM links between the BSC and the MSC. As shown in Figure 3.3, three PCM signals (this figure may be different depending upon the equipment manufacturer) coming from the MSC are multiplexed to one PCM signal towards the BSC. Figure 3.3 Transcoder/sub-multiplexer (TCSM) 3.2 TRANSMISSION NETWORK PLANNING PROCESS The transmission network planning process should generate a network plan that provides a high-quality network, with an immense amount of spare capacity at very low cost. In practice, a transmission planning engineer has to use his or her expertise to balance three factors: cost, quality and capacity. The process of transmission network planning includes five main phases before the final plan is generated, as shown in Figure 3.4. Although the process looks simple in theory, in practice it is much more complicated because there could be many iterations at each step before a final plan is ready. The process begins with data collection, including the requirements for capacity and quality that lay the foundation of the whole process. Other essential information relates to what transmission equipment is available (including capacities), quality targets, tools for transmission planning including link budget calculations, topologies that can be used, etc. The pre-planning phase focuses on the dimensioning aspects of the transmission network. The pre-planning starts with the inputs from the radio planning engineers. Once the number Network Requirements Site Survey, LOS Capacit