lying CAC At first, a simple scenario is considered where a single RAB type is provided by the UMTS network to all UEs. That means all user connections have the same peak rate repeak to transfer data. Moreover in this scenario it is assumed that elastic traffic is not subject to the Connection Admission Control (CAC) function (see section 3.3.4.3). Thus, all elastic traffic supported by the UMTS radio interface is accepted into the UTRAN transport network, and therefore, the maximum number of simultaneous connections to be transported on the lub link is not restricted. Thus the lub link with capacity C can be modeled as an M/G/R-PS model with R = C/rpeak, as explained in section 6.3.4. By applying the M/G/R-PS model, the average user application QoS in terms of mean transfer delay or mean application throughput can be estimated, which is derived from the expected sojourn time of the M/G/R-PS model. The extended M/G/R-PS model in section 6.3.6 has considered the impact of the TCP slow start and round trip times on the expected transfer delay, however there are still a few improvements that are required and made in the framework of this thesis to be suitable for the UMTS network: (1) It is found that RTT in equation (6.24) is assumed to be a constant value, but often it is a varying value as a function of link congestion. Given a limited lub link capacity, the experienced RTT can go up quickly in the case of high link utilization and thus it has significant impact on the achieved end-to-end delay QoS. Therefore, the increases of RTT in case of high link utilizations need to be considered. (2) Secondly most of the IP traffic (e.g. Internet) is asymmetric, i.e. the traffic amount on the downlink is dominant. This leads to that the experienced congestion on the downlink is usually more than on the uplink. Moreover, according to the asymmetric traffic property, the UMTS sets up different RAB rates on the uplink and downlink separately and therefore the transfer delay spent on the uplink and downlink can be also differe