nv - CU-SeeMe interoperation

Richard Cogger (R.Cogger@cornell.edu)
Wed, 2 Nov 1994 17:43:00 -0500

We will be using an unreleased version of the reflector code
tomorrow, for the Prince Charles event, which is able to translate (and
generally fudge up) headers between nv/vat and CU-SeeMe. The good news is
that it's working. Running nv and vat, you can connect to a CU-SeeMe
reflector (running the new code) via unicast, and send and receive audio
and video.

Now for the bad news: we're not going to be able to generally
release this reflector code soon because:

First issue: We're worried about releasing something that will
allow folks to unknowingly invoke link-melting bitblasts across the
Internet. The problem is that nv, designed for a primarily multicast
environment, does not provide any information the reflector could use to
know which video streams a participant is actually viewing (has a window
open for). So the reflector just sends them all. (Or it could send none
of them, but what would be the point? Perhaps we should limit to at-most-n,
but they would be sort of randomly chosen and the nv user would have no
control.) Even in a multicast environment, one could argue that streams
ought not be sent where no one is watching, but the odds are that someone
probably is and only one copy goes (+- the effects of tunnel topology vs.
real). With the CU-SeeMe unicast environment, it would be intolerable for
a busy reflector to just send a copy of everything to each nv. CU-SeeMe
streams are sent by the reflector only after a client indicates, stream by
stream that it wants to receive them. (In current implementation, the
client, by default, asks for the first 7 streams it hears about, but we're
going to change that.)

We're exploring with Ron Frederick how we might best be able to add
somehow a means for a unix system to send the info the reflector needs to
be able to prune (or not unprune) unwanted streams. Unfortunately, none of
the CU-SeeMe team knows UI programming for X. If anyone wants to help...

Second issue: nv sending via reflector to CU-SeeMe only works if nv
uses its CU-SeeMe encoder. So you can't in general use this new version to
watch an mbone conference with a Mac or PC. We plan to move nv's set of
decoders and the CU-SeeMe encoder into the reflector for general
transcoding, but that's proving a little tougher in practice than it sounds
just to say it. But there's no real obstacle to getting this done beyond
the time to do it.

Cheers, -Dick