Effective bandwidth reduction over WAN

From: Eric Meijer (res0t122_at_verizon.net)
Date: 07/30/05

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    Date: Fri, 29 Jul 2005 20:40:49 -0700
    To: <secureshell@securityfocus.com>
    
    

    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


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