n the case of GPRS/EGPRS networks) Calculation of the TRX and BTS is simple (just add up all those connected to one BSC). The number of PCMs that are connected to the BSC can decrease using the concepts of grooming, topology planning, etc., ensuring that the PCMs connected to the BSC are fully utilised. However, as the number of BSCs increases, the cost goes up astronomically. In smaller networks where just one BSC may be sufficient, the operators may prefer using two BSCs for protection purposes. In many cases, the number of SS7 Transmission Network Planning and Optimisation (signalling system 7) channels and LAPD channels that can be supported by the BSC are also taken into account. PCU Planning In EGPRS networks, the packet control unit (PCU) becomes an important part of the equipment planning exercise. The PCU is a plug-in unit that controls the EGPRS radio resources. It receives and transmits the transcoding and rate adaptation unit (TRAU) frames to the BTS and frame relay (FR) packets to the SGSN. Important aspects to remember when doing PCU equipment planning are: Number of Abis channels supported by the PCU Number of radio timeslots supported by the PCU Processing capacity of the PCU Number of TRXs and BTSs supported by the PCU Based on these factors, the number of PCU cards required can be calculated. 3.10 Timeslot Planning Timeslot allocation planning along with the 2 Mbps planning form a part of detail transmission network planning. Understanding the following features will help in making the strategy for TS allocation on the Abis. A good TS allocation plan is one that takes into account the next releases of software and hardware, BTS configurations, topologies, upgrades (due to traffic and signalling) in the near and far future, etc. 3.10.1 Linear TS Allocation In this model, the next TS is utilised automatically. Assume that the configuration of a BTS is 1 + 0 + 0. In this configuration, TS 1 and TS 2 are used. However, when the configuration becomes 1 + 1 + 0, TS 3 and TS 4 are used for the next cel