Re: Effective bandwidth reduction over WAN

From: Terry Browning (linux-focus_at_nihil.co.uk)
Date: 08/02/05

  • Next message: Mark Senior: "RE: passphrase/ssh2"
    Date: Tue, 02 Aug 2005 21:43:01 +0100
    To: e.meijer@verizon.net
    
    

    Eric Meijer wrote:
    > To SSH mailing list:
    >
    >
    >
    >
    >
    > I have a somewhat unusual question. I do not know if this issue is
    > truly a bug or just a feature of the protocol.
    >
    >
    >
    > 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. This test setup
    > was composed of two nodes hooked up through a WAN emulator. They were
    > connected using Gigabit Ethernet, but the rate was throttled back to 45
    > mbps (DS3 rate). All of the testing used an MTU of 1500 and files sizes
    > of 10 MB, 100Mb, 1 GB, and 5 GB. We ran FTP tests with the same setup
    > for a baseline. For SCP and SFTP we tried each of the three encryption
    > algorithms (3-des, arcfour, & blowfish). We then varied the WAN
    > latency. We are using the latest version of the Portable SSP for
    > Solaris. The OS is Solaris 8.
    >
    >
    >
    > 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?
    >
    >
    >
    > Eric Meijer
    >

    I don't know the answer to the question, but the problem rings a bell.
    Have you considered testing rsync-over-ssh under the same conditions?
    IIRC, one of the rsync design objectives was maintaining good throughput
    over high latency connections.


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