nv - CU-SeeMe interoperation

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


Folks,
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