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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Question about propagation and queuing delays
Tony Finch wrote: On Mon, 22 Aug 2005, Petri Helenius wrote:David Hagel wrote:This is interesting. This may sound like a naive question. But if queuing delays are so insignificant in comparison to other fixed delay components then what does it say about the usefulness of all the extensive techniques for queue management and congestion control (including TCP congestion control, RED and so forth) in the context of today's backbone networks? Any thoughts? What do the people out there in the field observe? Are all the congestion control researchers out of touch with reality?Co-operative congestion control is like many other things where you're better off without it if most of "somebody else" is using it. TCP does not give you optimal performance but tries to make sure everybody gets along.TCP performs much better if queueing delays are short, because that means it gets feedback from packet drops more promptly, and its RTT measurements are more accurate so the retransmission timeout doesn't get artificially inflated. A combination of WRED and friends doing tail- and head-drop would seem to be ideal for this. OTOH you rather want some queueing delays instead of packet drops if your RTT is high. Recovering from packet loss at >100ms is far slower than having 10ms added to the RTT. -- Andre
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