ut nowadays more "bandwidth greedy" applications like Internet traffic start to play a more important role in the UMTS network. The variation of the traffic mix, e.g. large percentage of Internet traffic, leads to the change of traffic properties, which results in different bandwidth demands for the dimensioning. Thus it is important to continuously observe the varying traffic pattern throughout the network dimensioning cycle. Finally, for dimensioning the overall network, the geographic distribution of traffic for each traffic class has to be taken into account. This is usually related to economic and demographic data, technological trends, user behavior, or relevant growth rates [KO02, SKO 02]. Traffic Characterization Traffic characteristics are service-specific. They depend on the applications on the user flow level. For example, for web traffic small requests sent in one direction are followed by large data transfers in the opposite direction. It results in an asymmetric traffic property while the communication-oriented services like telephony and video conferencing typically establish bi- directional sessions and as a consequence the resulting traffic flows between the end systems are usually symmetric. Moreover, the web traffic usually has a much higher bursty nature than the voice or video traffic. On the network level, it is not only relevant to the applications, but also associated with the means of aggregation of various user flows. The traffic characteristics on both user and network level need to be considered carefully for network dimensioning. By taking into consideration a correct traffic property, the required capacities can be dimensioned more appropriately. 4.2 Important Issues for UMTS Network Dimensioning 4.2.2 Network Topology Network topology refers to the layout of the network. The topology of the UTRAN depends on the coverage of the access network, the location of Node Bs and RNCs, as well as the structure for interconnecting Node Bs and RNCs, and core network nodes. Figure 4.2 shows four