ality and costs. 3.3 PRE-PLANNING IN TRANSMISSION NETWORK As we saw in Chapter 2, based on the capacity, coverage and quality targets, radio network planners arrive at the number of base stations required in a given region. The task of a transmission planning engineer will be to connect these sites, which will require knowledge of the existing network infrastructure and spare capacity. The locations of the BTS, BSC and MSC sites should be known as well, along with the present and future capacity requirements for each base station. Armed with that knowledge, the transmission planner needs to find out the required capacity of each link. This process is dependent upon the traffic generated by each base station, the ability to cross-connect and groom each site so as to make complete use of the PCM links. Also, the transmission media, future capacity and topology have their own individual impacts on the number of PCM links required to interconnect the base stations, and subsequently the base stations to the mobile. 3.3.1 One PCM Connection One PCM line consists of 32 time slots, as shown in Figure 3.5. Time slot 0 (TSO) is used for link management, while TS1 to TS31 are used for traffic and signalling. The bit rate of each TS is 64 kbps, and depending on the type of signalling, the TCH can be 16, 32 or 64 kbps. The PCM shown in Figure 3.5 is the PCM on the Abis interface. It contains the TCHs that carry the traffic from the transceiver (TRX), as well as the signalling associated with it. PRE-PLANNING IN TRANSMISSION NETWORK LINK MANAGEMENT TCH.1 TCH.2 TCH.3 TCH.4 TCH.5 TCH.6 TCH.7 TCH.8 TCH.1 TCH.2 TCH.3 TCH.4 TCH.5 TCH.6 TCH.7 TCH.8 TCH.1 TCH.2 TCH.3 TCH.4 TCH.5 TCH.6 TCH.7 TCH.8 TCH.1 TCH.2 TCH.3 TCH.4 TCH.5 TCH.6 TCH.7 TCH.8 TCH.1 TCH.2 TCH.3 TCH.4 TCH.5 TCH.6 TCH.7 TCH.8 TCH.1 TCH.2 TCH.3 TCH.4 TCH.5 TCH.6 TCH.7 TCH.8 TCH.1 TCH.2 TCH.3 TCH.4 TCH.5 TCH.6 TCH.7 TCH.8 TCH.1 TCH.2 TCH.3 TCH.4 TCH.5 TCH.6 TCH.7 TCH.8 TCH.1 TCH.2 TCH.3 TCH.4 TCH.5 TCH.6 TCH.7 TCH.8 TCH.1 TCH.2 TCH.3 TCH.4 TCH.5 TCH.6 TCH.7 TCH.8 TCH.1 T