Check out the new USENIX Web site. next up previous
Next: Related Work Up: Simulation Results Previous: Impact of Varying Simulation

Impact of Transmission Loss

Finally, we evaluate the impact of transmission loss on the response time for the different protocols. We consider transmissions with an average RTT of 25 ms and subject the packets to a constant loss rate, independent of the load in the system. Figure 11 graphs the results. The response time for TCP blows up with increased loss rates, since TCP interprets losses as signals of congestion. PCP and fair queueing can tolerate losses without suffering a substantial increase in response times. In PCP, when a loss is detected, either through a timeout or by the presence of acknowledgments for subsequent messages, the packet is scheduled for retransmission for the next available time slot based on the current paced transmission rate.

Figure: Performance over a lossy channel. Bottleneck bandwidth is 40 Mb/s, average RTT is 25 ms, flow lengths are 250 KB, and interarrival times are set to operate the system at 60% load. Fair queueing and PCP suffer no congestion packet loss.
\epsfig{file=graphs/lossvar/lat.eps, height=1.1in,width=1.7in} \epsfig{file=graphs/lossvar/latdev.eps, height=1.1in,width=1.7in} \epsfig{file=graphs/lossvar/qsz.eps, height=1.1in,width=1.6in} \epsfig{file=graphs/lossvar/loss.eps, height=1.1in,width=1.7in}


next up previous
Next: Related Work Up: Simulation Results Previous: Impact of Varying Simulation
Arvind Krishnamurthy 2006-04-06