Re: Effective bandwidth reduction over WAN

Eric Meijer wrote:
> To SSH mailing list:
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> I have a somewhat unusual question.  I do not know if this issue is
> truly a bug or just a feature of the protocol.
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> 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.
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> The results were
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> 0 latency      FTP – Ave. 39.5 mbps    SCP – Ave. 39.4 mbps      SFTP –
> Ave. 38.8 mbps
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> 60 millisec    FTP – Ave. 37.7 mbps    SCP – Ave.  2.9 mbps       SFTP –
> Ave.  2.9 mbps
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> 100 millisec  FTP – Ave. 33.0 mbps    SCP – Ave.   2.0 mbps      SFTP –
> Ave.  1.8 mbps
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> Can anyone tell me why the throughput of SCP and SFTP drop so
> drastically when we try to use SSP protocols over a WAN?
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> 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.