[AG-TECH] Unicast issues with vic/rat

Don Morton Don.Morton at umontana.edu
Mon Jan 26 19:48:15 CST 2004

Howdy folks,

In the past couple of weeks, working with two different
groups, I've run into a common problem and am wondering
if anybody has faced this sort of thing and can point
to potential solutions.

The basic problem in both cases is that folks are having
problems connecting vic/rat successfully VIA UNICAST to
a unicast/multicast bridge.  Quick example:

If you use my QuickBridge at U Montana, you should be
able to jump into the UM Institutional Venue and see
a couple of my cameras and hear some pleasant country
music playing :)

vic mroccs.cs.umt.edu/50186
rat mroccs.cs.umt.edu/50184

(If you do try this, please don't linger,
as there are "official" uses for this 
venue :))

Or, you should be able to access the AG Lobby via
my QuickBridge

vic mroccs.cs.umt.edu/50006
rat mroccs.cs.umt.edu/50004

For some reason, there are folks who are trying
to unicast in, and the end result seems to be that
"we" can see them, but they can't see us.  Note
that there's no multicast involved here - in one case,
the bridge is simply being used as a "rendezvous point"
for two unicast streams, but the same problems occur - 
I seem to be able to see/hear the remote site, but they
can't see/hear me.

Note that this only happens in very specific networks.
If these folks go outside their network (e.g. through an
ISP), it seems to work fine, so it's unique to specific

My vague understanding of vic/rat, used with the QuickBridge,
is that the clients send UDP datagrams out to the bridge on ports
in the 50000 range, and they seem to receive UDP datagrams on
ports in the 32000 range, and it "should" be that simple.
One of these sites swears up and down that their filters will
allow these UDP datagrams, and they've even tested it by trying
to push datagrams from the outside in, which seemed to work.

Is there something "additional" going on that might prevent
these unicast audio/video streams from getting into certain
networks?  I "have" to think others have run into this, and
there would be a lot of people quite thankful for your
sharing your war stories :) :)



   Don Morton                      http://www.cs.umt.edu/~morton/
   Department of Computer Science       The University of Montana
   Missoula, MT 59812 | Voice (406) 243-4975 | Fax (406) 243-5139

May your trails be crooked, winding, lonesome, dangerous, leading to the
most amazing view. May your mountains rise into and above the clouds.
-Edward Abbey, naturalist and author (1927-1989) 

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