Date: Sun, 22 Mar 1998 20:43:46 -0800 From: David Greenman <dg@root.com> To: Joao Carlos Mendes Luis <jonny@coppe.ufrj.br> Cc: chat@FreeBSD.ORG Subject: Re: ftp.cdrom.com limits ftp bandwidth ? Message-ID: <199803230443.UAA00349@implode.root.com> In-Reply-To: Your message of "Sun, 22 Mar 1998 17:25:16 -0300." <199803222025.RAA08589@gaia.coppe.ufrj.br>
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> My network is so logically close to California that most times it's >faster to fetch things from ftp.cdrom.com than from other parts of >Brasil. And I have always considered ftp speed measurements from >ftp.cdrom.com as a theoretical top limit on single connection bandwidth. > > When we first had our 2M international channel I tested the speed and >it was 34kBps for a single ftp transfer. It was not a limit on the >link, because I could open a second (and third, and fourth) simultaneous >ftp and get the same 34kBps. So I thought that was the TCP window >limit for Rio de Janeiro <-> California links. > > But yesterday (when miraculously we got full speed again), a friend >could get things from other places in USA at 50kBps and above rates. >I first thought that something changed in our international link and went >ftp.cdrom.com to test. Just to get the same 34kBps. So, it seems to me >that this 34kBps limit is particular to ftp.cdrom.com. > > Is this a software limit on DG's ftpd ? Or just a side effect from >the relatively small window used on ftp.cdrom.com to conserve memory ? >Or maybe http traffic has some performance advantage over ftp traffic ? >(I'm not complaining, I'm just curious. I would love if I could get >34kBps everyday and everytime. :) ) None of the above. The window is the 16KB default (and no, I do not plan to increase that), and we have no bandwidth limiting or other silliness. A ttcp test down to San Diego just now shows about 850KB/sec...it would be higher if the RTT was smaller (it's about 17ms). There are three explainations I can offer: 1) the RTT is sufficiently high that it is limiting the performance to the level that you are seeing - I'm seeing about 250ms right now to your gateway, or 2) congestion has become a problem again at MAE-west where the traffic is interchanged between CRL and cerf.net, or 3) there is enough packet reordering over CRL's aggregated MAE-west circuits that it is magnifying the effect of the large RTT and reducing the performance. Of these, I think this last possibility is the most likely. -DG David Greenman Core-team/Principal Architect, The FreeBSD Project To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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