Mobility

Unleashing Tor, BitTorrent & Co.: How to Relieve TCP Deficiencies in Overlays

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Executive Summary

Many overlay-based distributed applications employ TCP for the communication between peer nodes. Typically, the TCP connections of one peer will all share one physical Internet link. Using real-world network experiments, the authors demonstrate that this can lead to undesirable interactions between overlay links, resulting in oscillations and suboptimal throughput. Consequently, they argue that such effects should be taken into account in the design and deployment of overlay networks. In support of this case, they identify readily deployable countermeasures. In a first step, they show that simple traffic shaping mechanisms based on existing operating system QoS functionality can bring some relief. Yet, this alone is not fully effective if peers communicate bi-directionally, due to TCP ACK piggybacking.

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