der submulti- pleyer)/MSC needs to be planned. The following steps are performed for dimensioning the Ater interface: Total traffic (in Erlang) is offered through the Abis interface of a BSC. Define the blocking probability on the Ater interface. Apply the Erlang-B formula. Calculate the number of traffic channels, Y. Find the number of traffic channels that are carried by Ater, e.g. 120. Capacity required (in E1) = Y/120. Actual capacity planned = capacity required + spare capacity. For interface planning in EDGE networks, Abis interface planning is similar to that of GSM networks. However, if the feature of Dynamic Abis * is used then Abis interface planning in EDGE transmission networks is much more complicated than in GSM transmission networks. 3.6.2 Dynamic Abis Under this scheme, some of the timeslots on the Abis are reserved specifically for the packet data users. The planning is based on the coding schemes that are used in the EGPRS. In EGPRS, there are nine coding schemes used, each having its own data rate, as shown the Table 3.14. Based on the bit rates, the number of TCH required on the Abis to carry the traffic is calculated. These traffic channels are basically of two kinds: master and slave. First the TCH is the master and the rest are slaves, e.g. in the case of MCS-1, as there is only one TCH, it is a master; however, for MCS-7, first the TCH is master while the remaining three are slaves. In GSM Abis, almost 96 TCHs (i.e. subscribers) can be 'talking' at the same time. Due to the packet data requirements, the numbers of simultaneous users decreases in the EGPRS system and the Abis capacity becomes a bottleneck. Assume that there is one site that is EDGE capable. The capacity of the site is 4 + 4 + 4. In the case of the GSM network, the Abis will be able to carry 96 users. However, if the users need to access data services and have a requirement of the highest data rate that is possible. This means that there are 24 TSs present for traffic (with the assumption that TSO and TS31 are used for manag