the pool, p is the utilisation of EDGE channels in the air interface, and n is the number of traffic channels used in the air interface. This dimensioning will result in outputs such as the maximum throughput possible on the air-interface with Abis acting as a bottleneck, and the number of time slots required to allow maximum possible throughput on the air interface to be carried on the Abis. The Impact of Dynamic Abis on Transmission Network Design Assume that there is a base station site having a configuration of 3 + 3 + 3. When oper- ating in the GSM mode, using 16 kbps signalling, the required number of PCM time slots per transceiver is 2.25 (two for traffic and 0.25 for 16 kbps signalling). This means that the total number of time slots required for these nine TRXs is 9 X 2.25 = 20.25; i.e 21 time slots approximately. This would mean that, of 32 time slots, TSO and TS31 along with these 21 are used (23 in total), leaving nine time slots available for possible future upgrades. In an EDGE network, these nine time slots might be used for the DAP, if they are sufficient. Now consider this EDGE network using the MCS-9 coding scheme; i.e. each user logging on the network for PS services requires four Abis channels, or one full additional time slot, apart from the master sub-time slot on the PCM. This means that at a given time only nine EDGE: NETWORK PLANNING AND OPTIMISATION users can use the system at a maximum rate of 59.2 kbps. As soon as a tenth subscriber logs on to the network also requesting the MCS-9 scheme, the system starts sharing its resources. This means that although access will be given to this tenth subscriber, the request will be downgraded to lower coding schemes like MCS-6 or MCS-7. Also, the coding scheme of the existing subscribers logged on may be downgraded to MCS-6 or MCS-7, in order to accommodate this new subscriber. So the throughput on the air-interface goes down because of the limitation on the Abis interface. In this case it would be advisable to have more time slots in the pool, imp