ental behaviors of TCP. In the following a brief description of main TCP features and their consequences for the network dimensioning are given. Sliding Window Mechanism The sliding window mechanism is employed to control the amount of data that the sender is allowed to send to the network without having received an acknowledgement. A window size is defined, which constrains the number of packets that can be unacknowledged at any given time. It is a variable that equals to the minimum of the receiver window size (notated as rwnd) and the congestion window size (notated as cwnd). Receiver window size is advertised during connection establishment and indicates the maximum amount of data which the receiver buffer is able to hold. The congestion window is influenced by TCP flow control imposed by the sender, i.e. slow start and congestion avoidance (see introduction blow). The TCP sender uses the congestion window to adapt its data rate to the available network bandwidth. Once the sender receives an acknowledgement for the first packet in the window, it "slides" the window along and sends the next packet. The window continues to slide as long as acknowledgements are received. To allow continuous sending without any unnecessary waiting times, the window has to be equal to or larger than the bandwidth-delay product of 6 Dimensioning for Single ATM-Based lub the path between the sender and the receiver. This product represents the "capacity" of the network and is computed by BW . RTT. Parameter BW is the available bandwidth in the network, and RTT is the round trip time, i.e. the time period between sending a TCP packet and receiving the corresponding acknowledgement. With the sliding window mechanism, TCP can perform efficient transmission by allowing transmitting multiple packets before an acknowledgement; and it can provide flow control considering the receiver buffer size and the available network capacity. The sliding window mechanism will have impact on the obtained throughput of the TCP flows. In the case of a re