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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: packet reordering at exchange points
In message <[email protected]>, "Jim Forster" write s: >Sure, see the original Van Jacobson-Mike Karels paper "Congestion Avoidance >and Control", at http://www-nrg.ee.lbl.gov/papers/congavoid.pdf. Briefly, >TCP end systems start pumping packets into the path until they've gotten >about RTT*BW worth of packets "in the pipe". Ideally these packets are >somewhat evenly spaced out, but in practice in various circumtances they can >get clumped together at a bottleneck link. If the bottleneck link router >can't handle the burst then some get dumped. Actually, it is even stronger than that -- in a perfect world (without jitter, etc), the packets *will* get clumped together at the bottleneck link. The reason is that for every ack, TCP's pumping out two back to back packets -- but the acks are coming back at approximately the spacing at which full-sized data packets get the bottleneck link... So you're sending two segments (or 1.5 if you ack every other segment) in the time the bottleneck can only handle one. [Side note, this works because during slow start, you're not sending during the entire RTT -- you're sending bursts at the start of the RTT, and each slow start you fill more of the RTT] Craig
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