 phase and the maximum TCP window size is large enough to cover the bandwidth-delay product of the network. Let Cavailable denote the designated bandwidth share, which a sender is supposed to utilize in average once its window is large enough. For a given link capacity C, peak rate r peak, and link utilization p, this bandwidth per flow can be determined by Cavailable = peak / fR, where fR is the delay factor of the M/G/R-PS system. With Cavailable given TCP round trip time RTT, the time, after which a sender is able to utilize its fair share, can be calculated. This is the case when the congestion window is large enough to cover the bandwidth-delay product, i.e. when it reaches w* given in equation (6.22). MSS RTT (6.22) 6 Dimensioning for Single ATM-Based lub all necessary RTTs (round trip time) which are waiting for ACKs as a result of slow start transferred with available capacity Figure 6.19: Data transfer in TCP with slow start Due to the TCP slow start, the TCP congestion window size increases exponentially (assuming no packet losses in the slow start) with approximately 21 after i round trip times (i = 0, 1, 2 ...). Thus, the amount of data sent up to the time when the sender can start utilizing its bandwidth share, i.e. the window size reaches or exceeds w*, is denoted as Xslow-start calculated by equation (6.23): Xslow-start =2("-1)MSS with n (6.23) In equation (6.23), n* represents the time step in terms of RTT, at which the sender window is for the first time equal to or larger than w* The approximation of the expected transfer delay E{T(x)} for an object of size x (including overhead) is given in equation (6.24) by [RPBP00]: E{T(x)} = (6.24) n*RTT-osar) X slow-start As seen from (6.24), the computation of the expected time to transfer all data is divided into two parts according to Figure 6.19: the first part gives the sum of all necessary RTTs which are mostly spent waiting for acknowledgements as a consequence of the slow start mechanism; the second term considers the time of transmitting the rest 