[TriLUG] The DirecPC challenge

[Tarus Balog]

Okay. You guys seem to be pretty good, so let me throw out this challenge
for you.

I live in the woods, and the only high-speed Internet connectivity I can
get is DirecPC. DirecPC is an asynchronous system that uses the phone line
for upstream communication and a satellite for downstream traffic.

You communicate with the satellite via a satellite "modem" that connects
to a USB port. The software (which only comes for Windows) basically
creates a VPN between your system and a NOC in Virginia. Your outbound
requests go over the modem to the NOC, and the replies are sent down a
channel on the satellite.

Of course, it is very latent, but once large file transfers get going you
can see speeds between 400-600 kbps. Beats a 56K modem and it's all I got.

So, in my home network I have a Windows box running the DirecPC software
and Internet Connection Sharing. Thus it acts as a router and all of my
Windows computers run just fine.

The problem comes when I add Linux to the network. I can access the
network fine, but if I try and download anything over 100K (picture, mail
file, etc.) the system stalls and the transfer hangs.

I have tried playing with a number of settings, as well as trying some
more "robust" Windows routing software than ICS to no avail. So now I have
this big ol' kludge where I run all of my large network traffic on an SMB
share that I mount on my Linux boxen together with cygwin (go to the
Windows box, checkout CVS, go to the Linux box, develop, go to the Windows
box, cvs up, etc.)

One more piece of information. DirecPC has a mode where you can use the
phone line (called terrestrial mode) for all traffic. If I do this - no
stalls. So the problem does seem to be with the satellite down link and
not necessarily Windows ICS (the Windows client, again, work well).

Clues? My gut tells me that the ACKS may be getting lost/timing out due to
the funky setup. Oh, ECN is off. (grin)

-T

-- 
Tarus Balog
Consultant
Sortova Consulting Group, http://www.sortova.com
+1-919-696-7625
tarus at sortova.com