Re: Effective bandwidth reduction over WAN

From: Peter Kjellström (cap_at_nsc.liu.se)
Date: 08/05/05

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    To: secureshell@securityfocus.com
Date: Fri, 5 Aug 2005 18:41:15 +0200

    On Thursday 04 August 2005 19.04, Jeff Rosowski wrote:
    > >> The results were
    > >>
    > >> 0 latency FTP – Ave. 39.5 mbps SCP – Ave. 39.4 mbps SFTP –
    > >> Ave. 38.8 mbps
    > >>
    > >> 60 millisec FTP – Ave. 37.7 mbps SCP – Ave. 2.9 mbps SFTP –
    > >> Ave. 2.9 mbps
    > >>
    > >> 100 millisec FTP – Ave. 33.0 mbps SCP – Ave. 2.0 mbps SFTP –
    > >> Ave. 1.8 mbps
    > >>
    > >> Can anyone tell me why the throughput of SCP and SFTP drop so
    > >> drastically when we try to use SSP protocols over a WAN?
    >
    > Your problem is TCP itself. You can tweak your tcp window sizes, to let
    > you have more packets in flight. You could also use something that would
    > open multiple tcp connections for a single transfer.

    I disagree, since ftp runs as expected (just slight degradation) while
    scp/sftp takes a dive. I think the previously stated explanation involving
    the way ssh does it's own flowcontrol on top of tcp and the link to the
    efforts at PSC are more relevant.

    my .02 Euros
     Peter 

    -- 
------------------------------------------------------------
  Peter Kjellström               |
  National Supercomputer Centre  |
  Sweden                         | http://www.nsc.liu.se

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