
CPU SUN SPARCstation10
OS SunOS 4.1.3
ATM Swintch NEC ATOMIS 5
ATM Card SBA-200
Router NEC C&C-NET IP 45/650
AAL Type AAL5
MTU 9188octet
TCP Buffer Size 52428byte
Message Size 8196byte
Start Time HOST1->(Router)->HOST3: 0.00s
HOST2->(Router)->HOST3: 2.00s
number of send HOST1->(Router)->HOST3: 2000
HOST2->(Router)->HOST3: 500

When there is one data stream, the throughput is about 23Mbps. The bottleneck is the performace of the router. If you have not seen this graph, you may think that if there exist two data streams, each throughput must become about 11.5Mbps or greater and the sum of the throughput must be between 23Mbps to 32Mbps. However, it is WRONG! Data segments are transfered intermittently and each throughputs are terrible bad. The reason is thought that the router is overloaded. TCP must avoid congestion but TCP congestion avoidance mechanism functioning at the IP packet level dose not work well toward the congestion occured by the ATM cell level. ATM used by UBR mode is unfamiliar with TCP.