Date: 01 Aug 2001 23:32:29 -0400 From: stanislav shalunov <shalunov@internet2.edu> To: Bill Paul <wpaul@FreeBSD.org>, Ken Merry <ken@FreeBSD.org> Cc: freebsd-net@FreeBSD.org Subject: TCP problems with large window sizes on FreeBSD (GigaTCP) Message-ID: <87bslzt9v6.fsf@cain.internet2.edu>
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We want to build two or more machines that would be capable of achieving TCP throughputs of 700-800Mb/s over WAN (with a single TCP connection). The motivations of this exercise are spelled out on the referred web page. Additionally, I believe that getting through with this exercise with FreeBSD as the OS would advance FreeBSD's cause with network researchers and advanced users of high-performance networks. In order to run at such high throughput over links with RTT of roughly 70ms we'd need window sizes in the vicinity of 8-16MB. (And, naturally, the unidirectional loss event probability has to be less than (.7*MSS/(RTT*bandwidth))^2 = 1e-7. We believe that we have networks that lose less than one packet in ten million.) We have built the boxes now. I have started with back-to-back testing with large window sizes. Back-to-back testing is believed to be valid because it's hard to expect that inserting 70ms delay between the host will make the situation any better. I cannot get it to run with window sizes greater than half a megabyte. The story, with some very preliminary analysis, is at http://www.internet2.edu/~shalunov/gigatcp/ I'm not reposting it here; there are 29KB of text and 3MB of data there. I'm adding and updating stuff as I progress. The questions that I have for you guys are, in decreasing order of importance: 1. How do I fix the ti driver problem that apparently is holding me back? What number of jumbo slots would be "good"? 2. Why doesn't Fast Retransmit kick in? (See the annotated sender's view of the stalled connection.) 3. Is there an off-by-one error in RST handling? (See the end of the annotated receiver's view of the stalled connection.) -- Stanislav Shalunov http://www.internet2.edu/~shalunov/ "Nuclear war would really set back cable [television]." -- Ted Turner To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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