[p2p-hackers] Hard question....

Matthew Kaufman matthew at matthew.at
Sun Apr 2 03:45:32 UTC 2006


David Barrett:
> Has anyone else had good experience trying to 
> measure this automatically in the real world?

If you can accurately measure RTT, and accurately compute a transmit window
from observed loss the same way that TCP does, then you have all the raw
data necessary to know what the available bandwidth for a TCP-friendly flow
was over the last RTT.

And since you should be TCP-friendly, that bandwidth is in fact the
"available bandwidth", even if slightly more (or MUCH more, if the loss
isn't from congestion) actually exists.

And since you can't predict the future, and overall congestion and loss
varies much more rapidly than you might expect, you can't do any better than
knowing the past. Within one RTT, if you do it right... Worse, if you're
trying to calculate it from longer-term observations like algorithm-based
TFRC does.

Matthew Kaufman
matthew at matthew.at
http://www.amicima.com




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