RE: [Sip] Support for Multipart/MIME

"Christer Holmberg \(JO/LMF\)" <christer.holmberg@ericsson.com> Thu, 10 May 2007 01:55 UTC

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Subject: RE: [Sip] Support for Multipart/MIME
Date: Thu, 10 May 2007 03:55:23 +0200
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From: "Christer Holmberg (JO/LMF)" <christer.holmberg@ericsson.com>
To: Dan Wing <dwing@cisco.com>, Dale.Worley@comcast.net
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Hi, 

>The now-expired draft
http://tools.ietf.org/html/draft-jennings-sipping-multipart-02
>explored multipart/alternative.  One difficulty, however, is what does
it mean to say "can understand a part".
> 
>This is easy if one part is SDP and another part is SDPng.  
>If you understand SDPng, you process it; if you don't, you 
>process the SDP.
> 
>However, it's really hard if one part is SDP and another part 
>is also SDP -- in some cases we would like the answerer to 
>"pick the better SDP".

It doesn't always have to be about picking what is best.

For example:

Assume a terminal supports audio and video. If both audio and video are
used, it supports codecs audio_X and video_X.

However, if only audio OR video are used, the terminal has more
resources available, to it could use the more-resource-using codecs
audio_Y and video_Y.

In this case I don't think it's about picking based on what is "better",
it's about picking based on what will be used for the session. 

Now, I am sure there are other ways of doing this, but this solution
would not require support of any SDP extensions (multipart/alternative
would of course have to be supported), and the same port number could be
used for the audio and/or media m= lines in all alternatives.

Regards,

Christer






>At the time, we were considering multipart/alternative as a way to
offer RTP (RTP/AVP) and SRTP (RTP/SAVP), but we found >it doesn't work
well at all.
>Since then, draft-ietf-mmusic-sdp-capability-negotiation is a 
>superior solution to sending an offer containing RTP and SRTP.  
> 
> I suppose we could avoid the difficulty by prohibiting 
> identical Content-Types in the alternatives.
> 
> -d
> 
> 
> > -----Original Message-----
> > From: Christer Holmberg (JO/LMF)
> > [mailto:christer.holmberg@ericsson.com]
> > Sent: Thursday, May 03, 2007 3:50 AM
> > To: Dale.Worley@comcast.net; sip@ietf.org
> > Subject: RE: [Sip] Support for Multipart/MIME
> > 
> > 
> > Hi,
> > 
> > Multipart/alternative is interesting. I guess that, for 
> SDP, it could 
> > be used to provide different "offer alternatives". I think 
> it would be 
> > good to compare it against some of the other grouping/alternative 
> > mechanisms we have defined for that purpose.
> > 
> > Regards,
> > 
> > Christer
> >  
> > 
> > > -----Original Message-----
> > > From: Dale.Worley@comcast.net [mailto:Dale.Worley@comcast.net]
> > > Sent: 30. huhtikuuta 2007 19:13
> > > To: sip@ietf.org
> > > Subject: Re: [Sip] Support for Multipart/MIME
> > > 
> > >    From: Cullen Jennings <fluffy@cisco.com>
> > > 
> > >    I think the WG should consider an update to 3261 (likely done 
> > > through
> > >    the process Keith has proposed) that makes this 
> multipart/MIME  
> > >    mandatory to implement.
> > > 
> > > I assume that the requirement is that if a message has a 
> > > multipart/alternative body, and the UA is capable of 
> understanding 
> > > one part of the body, then it must be able to extract 
> that part and 
> > > use it to process the message.
> > > 
> > > Dale
> > > 
> > > 
> > > _______________________________________________
> > > Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> > > This list is for NEW development of the core SIP Protocol Use 
> > > sip-implementors@cs.columbia.edu for questions on current sip Use 
> > > sipping@ietf.org for new developments on the application of sip
> > > 
> > 
> > 
> > _______________________________________________
> > Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> > This list is for NEW development of the core SIP Protocol Use 
> > sip-implementors@cs.columbia.edu for questions on current sip Use 
> > sipping@ietf.org for new developments on the application of sip
> 


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