on is ftp of a 12 kbyte file size. Figure 6.24 compares the average file transfer delays derived from different processor sharing models against the simulations. M/G/R-PS Extended M/G/R-PS Adjusted & Extended M/G/R-PS Simulation (no CAC) Figure 6.24: Average file transfer delay over load: ftp scenario, RAB 128 kbps, no CAC, constant file size of 12 kbyte, lub link = 1 E1 line For a 12 kbyte file size, TCP flows remain mainly in the slow start phase. The offset between the basic M/G/R-PS (equation (6.18)) to the extended M/G/R-PS (equation (6.24)) under the low load is due to the underestimation of the delays caused by the slow start during which the available bandwidth cannot be fully utilized. When the load goes higher the shared bandwidth starts to be fully utilized, thus these two curves converge. The adjusted and extended M/G/R-PS model proposed in section 6.3.7.1 with equation (6.26) and (6.27) considers the impact of the slow start as well as the additional delay for setting up and releasing the TCP connection, and moreover the varying round trip time effect. It can be easily seen that the adjusted M/G/R-PS model proposed in the framework of this thesis matches the simulation results best. 6.3 Dimensioning for Elastic Traffic The following scenarios validate the accuracy of the M/G/R-PS model for different file sizes and file size distributions. Figure 6.25 presents the transfer delay over different load levels for a small file size of 5kbyte (left chart) and a large file size of 100kbyte (right chart). Both figures demonstrate that the adjusted and extended M/G/R-PS approach can predict accurately the average file transfer delay for different file size ranges. But the basic M/G/R- PS approach underestimates the transaction times: firstly it does not consider the extra delay caused by the TCP slow start and this relative offset is much more significant for smaller file sizes; secondly it does not consider the additional delay for connection setup and release. The extended M/G/R-PS approach improves the accu