Optimizing SSH for low speed links

Alex Satrapa grail at goldweb.com.au
Thu Aug 8 14:09:03 EST 2002


On Thursday, August 8, 2002, at 01:02 , Peter Barker wrote:

> Have you nailed the problem down to ssh, btw? Leaving all other 
> variables
> the same, substitute rsync/rsh (temporarily :-) and see if it makes a
> difference?

Or even try "cat"ing a large file.  I've had some experience with radio 
links in the past (I've even configured a Cisco to tunnel IPX over IP 
over PPP over radio - that was too much fun to have in one day!) and I 
know that "reliability" is a word often used in glossyware for a reason.

You may find that reducing the MTU will help maintain communication over 
that link - it reduces the amount of time that packets are in-transit 
over the PPP link for (since they're smaller), and simultaneously 
reduces the amount of retransmission that will occur due to stray gamma 
rays or car ignitions.

The radio I was using (way back in ancient history) presented a serial 
interface - so we ran PPP over the serial radio link.  I know some 
radios present an X.25 interface (let's take all the bad stuff about 
radio, and stick all the bad stuff about OSI on top!), so you configure 
the MTU (though I think they call it packet size) on the actual device, 
not at the PPP level.

Alex
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