Pre review of 3GPP MIME type for RTP payload format

[Larry Masinter]

Part of the problem is that RFC 3555 (MIME Type Registration
of RTP Payload Types) isn't marked as updating RFC 2048, even though
it seems to be intended to.

> [mw]
> The fact is that RTP and its signalling do require the 
> registration in the applicable. For RTP there is a clear 
> explanation in RFC 3550 why it is harmful to mix different 
> media types in the same RTP session. Due to this reason also 
> the signalling in SDP does not allow the mixing of multiple 
> media types in the same RTP session. So due to the above 
> restrictions one can not register an single 
> application/rtp.enc.aes128 to secure all the different media 
> top levels. 
> [\mw]

I looked at RFC 3550, and can find no mention
of MIME or any references to the media type registry,
so I don't understand where this 'clear explanation'
might be. There is a definition of a 'RTP media type':

   RTP media type: An RTP media type is the collection of payload
      types which can be carried within a single RTP session.  The RTP
      Profile assigns RTP media types to RTP payload types.

but I don't see what this has to do with MIME media types.
Can you be more explicit about where this is clearly explained?

It's hard to trace from 3555 and 3550 to the requirement that
different kinds of data need different top-level text/ audio/
video/ types.

Larry