Re: Effective bandwidth reduction over WAN

From: Darren Tucker (dtucker_at_zip.com.au)
Date: 08/02/05

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To: e.meijer@verizon.net

    Eric Meijer wrote:
    > I have two sites that are distantly connected to each other via a DS3
    > WAN. When we tried to replace FTP with SCP or SFTP we ran into
    > throughput problems. We then set up a test in our lab to see if we
    > could isolate the factor that was impacting throughput. [...]
    > We are using the latest version of the Portable SSP for
    > Solaris. The OS is Solaris 8.

    > Can anyone tell me why the throughput of SCP and SFTP drop so
    > drastically when we try to use SSP protocols over a WAN?

    Assuming by "Portable SSP" you meant "Portable OpenSSH", the current
    implementation does not use a "long, fat pipe" (ie one with a high
    bandwidth-delay product) very efficiently. Once the BDP gets larger
    than the SSH channel buffers those buffers become the bottleneck.

    There's some work over at PSC by Chris Rapier and Michael Stevens to fix
    this: http://www.psc.edu/networking/projects/hpn-ssh/

    With some code mods and TCP stack tuning they're getting some impressive
    improvements. 

    -- 
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
     Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.
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