Subject: [SIP] Video Conferencing?

From: Mark Lynch <[email-masked]>
Date: Wed, 7 Feb 2001 17:01:45 -0000

Hi,

I've been working with H323 for a while now but lately have been reading
alot about SIP and must say I'm very impressed with it's simplicity and
power. The only question I have is reagarding it's video conferencing
capabilities. I've been led to believe it's a long way off ? I thought it
was as simple as establishing an RTP channel and agreeing a codec. 

Could someone please tell me I'm wrong and point me to an example of Video
conferecing via SIP? I can' t seem to find any. 

If I'm right could anyone clarify what is happening in relation to this.

Regards,
Mark

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From: Henning Schulzrinne <[email-masked]>
Date: Thu, 08 Feb 2001 06:52:40 -0800

The spec contains several examples containing more than one media. If
you ignore things that don't belong in signaling protocols (such as
floor control), SIP will work just fine for any number of media. There
are a (small, unfortunately) number of user agents that support things
other than audio, but I've seen user agents supporting video, games,
text chat, shared whiteboards and shared applications, this being a
matter of adding the appropriate line to SDP, not of modifying SIP.

Thus, the lack of activity simply reflects the fact that there doesn't
seem to be anything special that is left to be done here.

This probably qualifies as a FAQ...

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From: Samir Chatterjee <[email-masked]>
Date: Mon, 12 Feb 2001 14:07:14 -0500

We are looking into collaboration technologies including video and the use of
SIP. I think SIP does not have to do much for handling video-conferencing
since SDP negotiation can simply have an added line describing the proper
codec to be used at either side. Then it goes to the actual media handler
where ports have to be opened and video to be handled. But there are some
other interesting issues that come up.
* In video-conferencing, I think there is no gateway involved. Because the
other end is most likely a IP host unlike VoIP where the terminating end could
be a dumb telephone. But could the other end be a TV set on a regular HFC
cable network that is not transporting IP over its reverse channels? Then the
Headend becomes a true gateway...opens up whole lot of issues.
* While 3-way calling and multi-party calling in voice has been handled, I
think the same analogies in the video-conferencing world have to be better
understood. What does it mean to bring another video source in to the
(multicast) session that is going on? Can a simple MCU handle all these video
mixing?
* QOS and bandwidth issues are probably stringent for video-conferencing.
* To promote SIP towards broader acceptance, everyone is trying to push for
new capabilities it brings to the table eg., web/telephony integration etc. I
really like the idea of thinking beyond current telephone handsets and
services we know of coming from the SS7 world. What about video services? We
have seen so far regular TV broadcast, pay-per-view, on-demand video and some
limited conferencing. Can anyone identify interesting video services along the
same lines as we have done in the  voice services world (which again
unfortunately many people do not use)?
* I think voice calls and pricing per minute have come up many times. Rate
arbitrage is an initial driver but not sustainable long term. What is the
pricing analogy for video services?
Samir
--
***************************************************************
Dr. Samir Chatterjee
Chairman, Co-founder & CTO
VoiceCore Technologies Inc.
Ph: 770-246-9973 | Fax:770-326-9922
email: [email-masked]
http://www.voicecore.com

(Also) Associate Professor
Computer Information Systems Department
J Mack Robinson College of Business
Georgia State University
Atlanta, GA 30303.
Ph: 404-651-3886
****************************************************************