nt. Thus, the distinction of uplink and downlink is necessary. It requires that the analytical model shall also consider the impact of the asymmetric traffic characteristic. (3) At last, the expected sojourn time given by equation (6.24) does not include 6.3 Dimensioning for Elastic Traffic the time spent for TCP connection setup and release phase. For an accurate modeling, the extra delay caused by the TCP connection setup and termination is suggested to be taken into account for the overall application delay or throughput performance. Varying RTT Extension It is assumed in this thesis that the increase of round trip times are mainly subject to the congested lub interface. To capture this impact of link congestion on the resultant RTT, an adjustment is suggested in this thesis to replace the constant RTT with RTT adjust. (RTT is the experienced round trip time during the low link utilization and fR is the delay factor) for equation (6.24). The expression of the average file transfer delay is improved with equation (6.26): x<xxlsw-start (6.26) nRauow x x x s low-start But it should be noted that the calculation of n in equation (6.23) is only dependent on the RTT experienced under the low link utilization SO that n* is a function of fR. That means, when the network is congested (fr > 1), n* becomes low, i.e. the number of time steps when the available shared bandwidth starts to be fully utilized is less. Uplink and Downlink Differentiation Extension In order to differentiate the uplink and downlink transmission, an additional parameter UL_rtt_ratio is introduced into the model, which is defined as the time spent on the uplink as a ratio of the complete round trip time. Thus (1- - UL_rtt_ratio) indicates the percentage of the time spent on the downlink transmission. If UL_rtt_ratio < 0.5, it means that the uplink path experiences smaller latency than the downlink. It is applied in equation (6.27). TCP Connection Setup and Release Extension Figure 6.20 shows the complete TCP procedure of transferring one file. It c