[MMUSIC] Multi-party use of draft-ietf-mmusic-t140-usage-data-channel

[Gunnar Hellström <[e-mail]>]

Christer,

This is not related to the reviews of 
draft-ietf-mmusic-t140-usage-data-channel, but rather a question on its 
use, and also related to the work with multi-party real-time text in 
draft-hellstrom-avtcore-multi-party-rtt-source and 
draft-hellstrom-avtcore-multi-party-rtt-solutions.

For the RTP based transport of real-time text, we have the situation 
that many implementations exist which do not support multi-party, and 
therefore I have drafted an sdp attribute a=rtt-mix to indicate 
multi-party capability. For an endpoint, it is an indication that it is 
able to understand the source of text and present it accordingly.

Now, the question about draft-ietf-mmusic-t140-usage-data-channel. In 
section 5.5 it specifies multi-party considerations, with the main 
alternative to open one more data channel per source between the mixer 
and the endpoint, and a possible fallback to prepare a mix with limited 
functionality for display in one display area with the sources inserted 
as readable text.

How would you see a mixer select between these two alternatives? When a 
third party enters the session, would the mixer just have a try to open 
a new data channel, and use it for the third party if successful, and 
use the fallback method if unsuccessful. Or would the 
draft-ietf-mmusic-t140-usage-data-channel use case also need an sdp 
attribute of the same kind as a=rtt-mix ?

Also, how would the endpoint know if it is in contact with a traditional 
mixer, so that it is sufficient to send its own text only in the first 
opened data channel, or if the mixer is some kind of session 
distribution unit, where the endpoint needs to transmit its own text 
copied in all connected channels?

If an attribute is needed, the a=rtt-mix can possibly be specified so 
that it is usable also for that case, or else the a=rtt-mix can be 
specified as an attribute with an extendable set of values, e.g. 
a=rtt-mix:rtp-mix and a=rtt-mix:multi-chan . What is your (or anybode 
else's) view?

Regards

Gunnar

-- 

+ + + + + + + + + + + + + +

Gunnar Hellström
Omnitor
[e-mail]
[phone]