Abstract of "The Effects of Active Queue Management on Web Performance: The good, the bad, and the ugly"

The Effects of Active Queue Management on Web Performance: The good, the bad, and the ugly


A colloquium given the Uiversity of Pennsylvania, Philadelphia, PA, April, 2004.

Abstract: Active queue management (AQM) refers to the process of running a decision procedure in a router when a packet arrives to determine if the end-system generating the packet should receive a signal that the network is congested. Active queue management in Internet routers has been proposed as a solution to some of the scalability issues associated with TCP's pure end-to-end approach to congestion control.

This talk presents an empirical study of the effects of AQM on the distribution of response times experienced by a population of users browsing the web. Three prominent AQM schemes are considered: the Proportional Integrator (PI) controller, the Random Exponential Marking (REM) controller, and Adaptive Random Early Detection (ARED). The effects of these AQM schemes were studied alone and in combination with an IP signaling protocol, explicit congestion notification (ECN).

The major results are:

Unless loads on network links are approaching saturation (e.g., loads above 80% of link capacity), there is little, if any, benefit to employing AQM.
When AQM is combined with ECN, both PI and REM provide significant response time improvement on saturated network links (e.g., at offered loads above 90% of link capacity), and provide response times competitive to that achieved on an unloaded network.
ARED, the most widely studied and tuned AQM scheme, consistently resulted in the poorest response times that were often poorer than those achieved without AQM.

We conclude that without ECN there is little end-user performance gain to be realized by employing the AQM designs studied here. However, with ECN, response times can be significantly improved. In addition it appears likely that provider links may be operated at near saturation levels without significant degradation in user-perceived performance.

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