Table 4.2). Each group of users generates different amounts of traffic and a distribution of subscribers to these user types enables a more accurate estimation to be made of network traffic. While business subscribers may generate higher traffic per subscriber (e.g. 45 mErl/subscriber), nonbusiness category subscribers would usually generate lower traffic (e.g. 18 mErl/subscriber) and even less for pre-paid subscribers (e.g. 10 mErl/subscriber). It would therefore be important to make as detailed a study as possible to estimate the correct traffic amount and their sources. Generally each subscriber group may be considered separately when dimensioning the traffic before adding all the traffic together to get the total traffic in the network. A tool for this purpose may be necessary. If it is not possible to specify the ratio of different subscribers in the different subcategories, then it is sufficient to take an average amount of traffic per subscriber (in mErl) and assume a single sub- scriber category. In expansion projects of an existing network, it is possible to get the number of active subscribers from MSC/VLR measurements of active subscribers in the VLR database during the busy hour (BH). Network Service Deployment A careful study of planned and existing services should be done in order to assess its impact on the network. Some of the basic services are voice telephony, value-added services, Internet, intelligent network (IN) Core Network Planning and Optimisation VMS listen IVR traffic Mobile originating Outgoing To own NW Loop back of incoming Mobile terminating Incoming VMS forwarded Interswitch Figure 4.2 Definitions of interswitch traffic (VMS, voice mail server; IVR, interactive voice response) services, etc. Details of the services to be supported by the network and their usage should be documented. Consider service growth and forecasts for different service types. Service penetration can provide important input on the number of subscribers in the network using the service. This information should 