Subject: [MMUSIC] Video phone and offer/answer model

From: Jun KOSHIKO <[email-masked]>
Date: Wed, 05 Jan 2005 15:15:20 +0900

Hello Folks,

Is there anything which bundle a number of m= lines of SDP?  I would
like a session to be established only when the offerer and the answerer
agree in the codec of both video and audio. Otherwise, the answerer
would reject the offer. (see the following sequence)

video phone#1                       video phone#2
 (offerer)                            (answerer)
     | (offer)                            |
     | m=audio ...                        |
     | m=video ...                        |
     |----------------------------------->|
     |                                    |
     |                           (answer) |
     |                        m=audio ... |
     |                        m=video ... |
     |<-----------------------------------|

But according to examples in RFC3264 (offer/answer model), each m= line
(video/audio/etc...) seems like being dealt with independently. So a
session would be established when they agree in the codec of ether audio,
video or etc. If the offerer and the answerer agreed in the codec of
video and they didn't agreed in that of audio, they establish a session
and there becomes a video phone service without voice.

I would like to avoid this situation. And I'm looking for the means that
enables offerers to desire the video/audio communication at a time.

Could you give me some advice?

Regards,
Jun

---------------------------------------------------------
Jun KOSHIKO
Next Generation Strategy
Research and Development Center
NTT-east Corporation

Telephone  +81 3 5359 5104
Facsimile  +81 3 5359 4768
E-mail: [email-masked]
19-2 Nishi-shinjuku 3-chome Shinjuku-ku Tokyo 163-8019 Japan
---------------------------------------------------------

_______________________________________________
mmusic mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/mmusic

---

From: Paul Kyzivat <[email-masked]>
Date: Wed, 05 Jan 2005 09:14:27 -0500

> video phone#1                       video phone#2

The callee is free to apply this kind of policy now. In fact, a limited 
form of it is quite common: a voice-only endpoint that receives an 
offerthat doesn't include voice, so that the answer would contain no 
accepted media, will usually fail the call. Similarly a voice+video 
endpoint could do the same if it doesn't receive an offer containing both.

But I think your issue is that the *caller* doesn't want the call to 
succeed unless there is both voice and video. I don't know of any *good* 
way to do this currently.

This could be solved with preconditions, if both sides support them. It 
doesn't matter much what the precondition is, so long as the caller can 
prevent it from being resolved in this case. For instance, you could put 
an unresolved QoS precondition on the voice, and fail the call rather 
than resolving it if you don't get an answer containing video.

	Paul