reject ratio of the circuit-switched traffic. These two models have been demonstrated to be appropriate analytical models for dimensioning a single lub transport link in both ATM and IP based UTRAN. In this chapter, they are proposed to be applied for dimensioning the multi- lub RAN as well, but some extensions are required to consider both the last mile link and the backbone link for calculating an end-to-end QoS. For the dimensioning process, two issues are discussed and investigated in this chapter. The first issue is to develop methodologies to properly dimension the last mile links and the backbone link individually in order to fulfill the user QoS requirements on an end-to-end basis. The second one is to perform overbooking on the backbone link, given a number of last mile links each carries a certain amount of traffic. 8.1.1 Dimensioning of Individual Links The objective of this task is firstly to develop correct methods to estimate the end user QoS, taking into account of the impact of both last mile link and the backbone link on the end-to-end quality of service. To analytically estimate the end user QoS, the analytical models which were proposed to estimate the end user QoS in the single lub link scenario can be applied here in a way that the impact of the last mile link and the backbone link are considered. Then in the second step based on the relations of the user QoS with the individual links, appropriate dimensioning approaches need to be suggested to determine the bandwidth for the last mile link and the backbone link separately, which shall result in a minimum overall network cost while fulfilling the desired end-to-end user QoS requirements. 8.1.2 Overbooking of the Iub Backbone Link Overbooking means reserving more resources than are actually available. The nature of network traffic is usually "bursty". It allows active connections to utilize the bandwidth during the idle period of other connections. Hence a statistical multiplexing gain can be achieved in the aggregated traffic, especially for 