Fairness of AQM schemes for TCP-friendly traffic

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The increasing deployment of unresponsive streaming applications has triggered the design of a number of new mechanisms and protocols to reduce the potential risk of unfairness and congestion collapse in the Internet. Fair non-per flow active queue management (AQM) schemes, such as BLACK, have recently been proposed to maintain fairness when unresponsive constant bit rate UDP flows share a bottleneck link with responsive TCP traffic. Similarly, TCP-friendly protocols have been developed to provide smooth congestion control that is suitable for multimedia applications while still being compatible with TCP. However, the performance of these fair AQM mechanisms has not been evaluated when different TCP-friendly flows compete against TCP versions. As TCP-friendly protocols react to packet drops differently from TCP, the various AQM schemes might punish some flows unfairly. However, this aspect has not been studied yet. The paper provides two key contributions. First, it provides the first comprehensive evaluation of fair AQM schemes under the presence of various types of TCP friendly traffic. From experimental results, we found that a fair AQM scheme must be chosen not only based on its performance or capability to deal with unresponsive flows as is usually done, but also considering its performance when other types of flows are included, such as TCP-friendly sources. Second, the paper presents an enhanced version of BLACK that outperforms all of the other fair non per-flow state information AQM schemes.