Re: Effective bandwidth reduction over WAN

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)
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