Pre review of 3GPP MIME type for RTP payload format

Magnus Westerlund magnus.westerlund at
Thu Sep 2 09:58:15 CEST 2004

Hi Larry,

Comments below

Larry Masinter wrote:

> Thanks, I now understand. The main thing is that
> SDP takes the MIME type and uses the top level type
> for signaling.
> I wonder, though, whether you might instead register
> these things as "application", add a parameter, e.g.,
> "embedded-type", and then change the mapping
> between MIME types and SDP descriptions such that
> application/whatever;embedded-type="video" 
>   =>   m=video
> so as to avoid having to register N types for
> every wrapper mechanism.

Do we actually gain anything with not registering the type in all 
relevant media type? The reason is for example if you are finding a SDP 
and it contains an unknown type audio/whatever. Then if you like to 
determine what the type actually are and goes to IANA. I would assume 
that you would go looking at audio in the tree, rather than application.

Secondly, most types even wrappers may actually need to consider what 
media types they should be used at all. We also have these types that 
are more specific, but still are useful in multiple media types, like 
RFC 2198, that are used both in audio and text.

Is there any gain by doing a single type, using parameters more than 
purely administrative compared to registering them in each necessary 
media type?


Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund at

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