Re: [MMUSIC] I-D ACTION:draft-ietf-mmusic-sdp-media-content-04.txt

On 25 Jul 2006, at 14:03, Arnoud van Wijk wrote:
...
> PSTN textphone is a different content then subtitles or plain  
> vanilla ToIP.

No, it is not -- this is disconnect. A PTSN text phone is a device  
with only limited capabilities. That the device has limited  
capabilities is orthogonal to the content of the media stream  
produced by the device. I can use a text phone to send subtitles, or  
I could use it for the main speaker in an event, for example. The  
content can change; the fact that it is a text phone cannot.

One is metadata describing WHAT is being sent ("this is the main  
speaker"), the other is metadata describing mechanics of HOW it is  
being sent ("the main speaker is using a PTSN text phone via a  
gateway"). They're not the same type of information, and they  
shouldn't be confused at the signalling level.

> I appreciate the fact that you want to solve this and publish a  
> draft on
> that. I will surely study that when I see it floating on the MMUSIC  
> mailing
> list.

It simply takes the text from the current draft which defines  
"a=content:txp" and uses it to define an "a=txp" attribute instead.  
All the other mechanisms you and Gunnar have described to signal PTSN  
text phones can be used in their currently defined manner. I simply  
wish to separate the description of a stream's contents from the  
description of the capabilities of the device producing that stream,  
at the SDP level.

Colin

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