[c-nsp] what limits bw on a tcp stream?

[Robert E. Seastrom]

Peter Lothberg <roll at Stupi.SE> writes:

>> >> I have gear in Amsterdam and in San Jose.  Pushing log files from 
>> >> Amsterdam to San Jose through rsync seems to top out at 7Mbps even 
>> >
>> > Is rsync using ssh to move the data?  ssh has its own windowing
>> > issues.  There's a high perf fix for that which you should be able
>> > to find via google.
>> This.  http://www.psc.edu/networking/projects/hpn-ssh/
>> Modern TCP stacks deal OK.  7Mbps at that distance is about right for
>> ssh-constrained.
>>                                         ---Rob
>
> We did over 4Gbit/s with two mail-order PC's in 2004 over a
> best_effort comercial IP network at about 0.5s RTT.
>
> http://proj.sunet.se/LSR3-s/

Yep, and that required only modest tweaks to the kernel parameters.
Wasn't running over ssh though.  The internal buffers on off-the-shelf
openssh break performance pretty seriously for long fat pipes (unless
the hpn-ssh mods have been integrated back into production openssh,
which I'd really love to hear).

                                        ---Rob