d by the clock through the caesium PRC or the GPS. However, some networks may also supply the clock to the MSC through the PSTN networks. The BSC receives the clock from the MSC. The MSC transfers the clock to the SDH and through the retiming function the clock is transported to the BSC. The BTS receives the clock from the BSC in a manner similar to the clock transfer from the MSC to the BSC. There are a few things that transmission planning engineers should know when planning synchroni- sation in a cellular network: The clock always flows from the MSC to the BSC and the BSC to the BTS. The MSC gets the clock from the PRC. The maximum number of equipments in a chain should be limited; e.g. the number of SSUs should not be more than 10. Jitter and wander become accumulated when the synchronisation chains are long. Thus, long chains should be avoided. When planning synchronisation in a loop, there should not be any synchronisation loops. For this purpose, the master control bit (MCB) and the loop control bit (LCB) are used in TS planning. To maintain the quality of a synchronisation network, a highly accurate clock should be used as the PRC and there should always be more than one clock source available at all times for the equipment/element needing synchronisation. An example of a typical synchronisation network is shown in Figure 3.71. Transmission Network Planning and Optimisation N X SECs N X SECs K-1'th N X SECs K ('th N X SECs Figure 3.70 Synchronisation chain Re-Timing PRC (Caesium) 2 Mbit/s 2 Mbit/s SDH RING Rubidium 2 Mbit/s 2 MHz synch. interface Figure 3.71 Typical synchronization network Transmission Management 3.12 Transmission Management Management of the cellular network from one central location is very important for the operator, given the area size of the cellular network, where the sites may not only be located far away but also at not SO easily accessible locations. Thus, a centrally located network management system as handy for the operators. An advanced management system gives the operator to