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,
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
The major results are:
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.
- 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
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