TCP Protocols and Unfair Advantage – Being the Ultimate Pig on the Bandwidth Block

Little item from the testing side of proposed TCP protocols on stack fairness from the Hamilton Institute at the National University of Ireland, Maynooth.

According to Douglas Leith:
“In summary, we find that both Scalable-TCP and FAST-TCP consistently exhibit substantial unfairness, even when competing flows share identical network path characteristics. Scalable-TCP, HS-TCP, FAST-TCP and BIC-TCP all exhibit much greater RTT unfairness than does standard TCP, to the extent that long RTT flows may be completely starved of bandwidth. Scalable-TCP, HS-TCP and BIC-TCP all exhibit slow convergence and sustained unfairness following changes in network conditions such as the start-up of a new flow. FAST-TCP exhibits complex convergence behaviour.”

What’s this mean? Simple. In order to get more for themselves these approaches starve everyone else – the “pig at the trough” mentality. But what might work for a single flow in a carefully contrived test rig can immediately start to backfire once more complex “real world” flows are introduced.

There have been concerns for years that these approaches could wreak havoc on the Internet if not carefully vetted. I’m pleased to see someone actually is testing these proposed protocols for unfairness and the impact on network traffic. After 30 years of tuning the Internet, taking a hammer to it protocol-wise isn’t just bad science – it’s bad global policy.

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