Preliminary Report of Performance Results for TCP over ATM with Congestion

r, through a single switch, causing congestion at one of the switch output ports. Each TCP connection has it's own VC. A topology of five TCP s was chosen to model the case of multiple connections. The number of TCPs was increased to 10 for comparing performance when congestion increases. For all links, the bandwidth is 141 Mbps, chosen instead of 155 Mbps, so that the cell time is an integral number, 3 microseconds. The traffic model used for the initial study is an infinite stream of data, chosen because it represents the worst case for creating congestion. TCP ack packet size is 40 bytes. A LAN environment is modeled, in which the propagation delay is 3 or 5 microseconds from each host to the switch. The switch speedup factor is 2, typical of a LAN switch. Packet size, buffer size, and window size are varied in the experiments. Performance measures include each TCP connection's goodput, i. e., throughput without retransmissions, it's packet retransmission rate, and the number and r