Performance of high-speed TCP variants over the UKLight optical link

Testbed Configuration


The figure above depicts the simple dumbbell network testbed used in these experiemnts.
TCP Source1 and TCP Source2 send a (high-speed) flow to TCP Sink1 and TCP Sink2. The two pairs of senders/receivers are at teh two ends of the UKLight optical loopback, which has an RTT of approx. 177ms. iperf is used to transmit TCP data and measure throughput. We modified iperf to log TCP-related variables (ssthresh, cwnd, rto, rtt), using the tcp_info struct.  Traffic is routed via a Linux machine running as router, using iproute2's tc. Each machine is connected to 1Gbps NICs. Traffic from the router to the receiving ends is going via a gigabit Cisco 3750 switch. 

Experiment 1 (Router Queue=25%BDP, SACK ON, tso OFF, two flows):