Re: Effective bandwidth reduction over WAN

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Date: Tue, 2 Aug 2005 08:06:46 +1000
To: <e.meijer@verizon.net>

These people:
http://www.psc.edu/networking/projects/hpn-ssh/

have been working on a High Performance Enabled SSH/SCP

 From their page:
"SCP and the underlying SSH2 protocol implementation in OpenSSH is
network performance limited by statically defined internal flow
control buffers. These buffers often end up acting as a bottleneck
for network throughput of SCP, especially on long and high bandwith
network links. Modifying the ssh code to allow the buffers to be
defined at run time eliminates this bottleneck. We have created a
patch that will remove the bottlenecks in OpenSSH and is fully
interoperable with other servers and clients. In addition HPN clients
will be able to download faster from non HPN servers, and HPN servers
will be able to receive uploads faster from non HPN clients. However,
the host receiving the data must have a properly tuned TCP/IP stack."

It may help you out here...

Cheers,
Kai

On 30/07/2005, at 1:40 PM, 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
>
>

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