[e2e] Changing dynamics
huitema at windows.microsoft.com
Sat Feb 21 11:13:37 PST 2009
> Most (not all) of these ideas seem to reflect the idea that we should
> operate the net with a lot of internal buffering.
This is more or less required if we expect transport to use congestion control based on windows sizes. By definition, such controls can lead to great swings. Each transport connection will be a window that matches its share of the transmission resource and one or 2 RTT. In theory, they are more or less spaced over time, and the law of big numbers apply. But if for any reason they fire all at once, then the routers will see quite an incoming wave of traffic.
Window based control also has a spiraling effect on RTT. As more stations use the link, queues will build up. In the absence of losses, the stations will react by increasing the windows size, which will tend to further increase the queues.
I believe that if we want to get small queues, we have to implement some form of rate-based flow control, so we tame the peaks of traffic that any given station can generate.
-- Christian Huitema
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