Networking Investigate

Modeling Congestion in Backbone Routers

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Executive Summary

Traffic engineering models based on end-to-end loss probabilities and delays do not scale well to fast backbone links. In this paper, the authors investigate the nature of congestion events in highly aggregated flows. An examination of congestion events shows distinct phases of queue buildup, packet dropping followed later by TCP reaction, and queue clearing. Evidence of the existence and characteristics of these discrete congestion events is presented using active probe data gathered by the Surveyor project. When connections pass through periodic congestion, the aggregate offered load to neighboring links rises and falls in cadence with the congestion events. They named this group of connections a "Flock" and investigate the implications.

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