latively small receiver window size, the sender may not fully utilize the bandwidth of the network, as the capacity of the receiver buffer limits the rate of the sender to transmit packets. If it is assumed that the receiver has sufficient buffer size to cover the respective bandwidth-delay product of the network, then the resultant throughput will be only dependent on the accessible network bandwidth and the flow control functions at the sender. For an accurate dimensioning, the proposed dimensioning model should be able to capture the effect of the window mechanism. Slow Start Mechanism The slow start mechanism is a way to avoid network congestion after a new connection is established and the sender starts transmitting data. As the available network bandwidth unknown to the senders at the beginning, instead of injecting a large amount of data into the network at once, the sender starts transmitting data slowly to explore the network to determine the available capacity. As shown in Figure 6.14, at first the sender starts with only one segment, i.e. the TCP congestion window (cwnd) is initialized to one segment. For each received acknowledgement the congestion window is increased by one segment. This leads to an exponential increase of cwnd until the receiver window size (rwnd) is reached. duplicate ACKs window size packet rate timeout duplicate ACKs congestion congestion avoidance avoidance slow start time in seconds Figure 6.14: TCP slow start and congestion avoidance [Rie04] 6.3 Dimensioning for Elastic Traffic During the slow start phase, the available bandwidth assigned to the connection cannot be fully utilized. Therefore, the slow start mechanism slows down the transmission process and thus degrades the end-to-end QoS. Especially, this effect becomes more considerable for longer round trip times and small file transfers. Thus, for these cases it is necessary to take the slow start mechanism into account in the dimensioning model. Congestion Avoidance Algorithm While the slow start mechanism is used to avoi