The Effects of Active Queue Management and Explicit Congestion Notification
on Web Performance
- L. Le,
- IEEE/ACM Transactions on Networking
- Volume 15, Number 6, December 2007
- pages 1217-1230.
We present an empirical study of the effects of active queue management (AQM)
and explicit congestion notification (ECN) on the distribution of response
times experienced by a population of users browsing the Web. Three prominent
AQM schemes are considered: the Proportional Integral (PI) controller, the
Random Exponential Marking (REM) controller, and Adaptive Random Early
Detection (ARED). The effects of these AQM schemes were studied with and
without ECN. Our primary measure of performance is the end-to-end response
time for HTTP request-response exchanges. For this measure, our major results
We conclude that AQM can improve application and network performance for Web
or Web-like workloads. In particular, it appears likely that with AQM and
ECN, provider links may be operated at near saturation levels without
significant degradation in user-perceived performance.
- If ECN is not supported, ARED operating in byte-mode was the best
performing AQM scheme, providing better response time performance than
drop-tail FIFO queuing at offered loads above 90% of link capacity.
However, ARED operating in packet-mode (with and without ECN) was the
worst performing scheme, performing worse than drop-tail FIFO queuing.
- ECN support is beneficial to PI and REM. With ECN, PI and REM were the
best performing overall schemes, providing significant response time
improvement over ARED operating in byte-mode. In the case of REM, the
benefit of ECN was dramatic. Without ECN, response time performance with
REM was worse than drop-tail FIFO queuing at all loads considered.
- ECN was not beneficial to ARED. Under current ECN implementation
guidelines, ECN had no effect on ARED performance. However, ARED
performance with ECN improved significantly after reversing a guideline
that was intended to police unresponsive flows. Nonetheless, overall,
the best ARED performance was achieved without ECN.
- Whether or not the improvement in response times with AQM is significant
(when compared to drop-tail FIFO), depends heavily on the range of
round-trip times (RTTs) experienced by flows. As the variation in
flows' RTT increases, the impact of AQM and ECN on response-time
performance is reduced.
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