Subject: Re: [MMUSIC] Re: Multiple 'm' lines with the same port number

From: Rajesh Kumar <[email-masked]>
Date: Thu, 01 May 2003 07:11:49 -0700

At 07:10 PM 4/28/2003 -0400, Jonathan Rosenberg wrote:
>Using two m lines to represent alternate encodings for a stream is not 
>consistent with the offer/answer model, IMHO. RFC 3264 has mechanisms for 
>transitioning from audio to fax, for example, but these require a 
>re-invite to do:
>
>8.3.3 Changing Media Types
>
>    The media type (audio, video, etc.) for a stream MAY be changed.  It
>    is RECOMMENDED that the media type be changed (as opposed to adding a
>    new stream), when the same logical data is being conveyed, but just
>    in a different media format.  This is particularly useful for
>    changing between voiceband fax and fax in a single stream, which are
>    both separate media types.  To do this, the offerer creates a new
>    media description, with a new media type, in place of the description
>    in the previous SDP which is to be changed.

How about the use of capability sets as described in RFC 3407? The 
alternate encodings which may be triggered on specific stimuli can be 
expressed as latent capabilities, as in the examples inRFC 3407.

Perhaps, the offer-answer model, RFC 3264, needs to be expanded to include 
the use of latent capabilities.

Rajesh

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