Re: Effective bandwidth reduction over WAN

On Thursday 04 August 2005 19.04, Jeff Rosowski wrote:
> > > The results were
> > >
> > > 0 latency      FTP â Ave. 39.5 mbps    SCP â Ave. 39.4 mbps      SFTP 
> > > â
> > > Ave. 38.8 mbps
> > >
> > > 60 millisec    FTP â Ave. 37.7 mbps    SCP â Ave.  2.9 mbps       SFTP 
> > > â
> > > Ave.  2.9 mbps
> > >
> > > 100 millisec  FTP â Ave. 33.0 mbps    SCP â Ave.   2.0 mbps      SFTP 
> > > â
> > > 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?
>
> Your problem is TCP itself.  You can tweak your tcp window sizes, to let
> you have more packets in flight.  You could also use something that would
> open multiple tcp connections for a single transfer.

I disagree, since ftp runs as expected (just slight degradation) while 
scp/sftp takes a dive. I think the previously stated explanation involving 
the way ssh does it's own flowcontrol on top of tcp and the link to the 
efforts at PSC are more relevant.

my .02 Euros
 Peter

-- 
------------------------------------------------------------
  Peter KjellstrÃm               |
  National Supercomputer Centre  |
  Sweden                         | http://www.nsc.liu.se

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