Re: [MMUSIC] Possible BUNDLE alternative syntax: explicit m-line for bundled session

"Ejzak, Richard P (Richard)" <> Thu, 20 September 2012 19:19 UTC

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From: "Ejzak, Richard P (Richard)" <>
To: Christer Holmberg <>, "" <>
Thread-Topic: [MMUSIC] Possible BUNDLE alternative syntax: explicit m-line for bundled session
Date: Thu, 20 Sep 2012 19:18:49 +0000
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Subject: Re: [MMUSIC] Possible BUNDLE alternative syntax: explicit m-line for bundled session
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> > m=bundle requires significant extensions to the syntax and also a near
> doubling in the size of the SDP.  It is harder to specify allowed
> > combinations of codecs and other options that are normally associated
> with a single m line.
> Please give an example.

To specify two types of audio flows with very different characteristics I would normally have separate media lines with separate codec lists and attributes.  One may require DTMF and the other silence suppression in addition to the selected (but different) codecs.  We need to keep this characteristic.  We also need a way of specifying bandwidth per (old) media line, which is already supported using separate media lines but requires that something new be defined for m=bundle.  What about RTCP characteristics?  We certainly want to specify them per (old) media line.

I understand that this can be done with m=bundle, but it requires new syntax.  Why bother if we have something that can work?

> You have said that we need a second offer/answer, with the same port
> numbers, in order to handle intermediaries. I don't understand why the
> first offer could not be without bundle, and the second offer (once you
> know that the remove endpoint supports bundle) according to the current
> mechanism, with the same port numbers.

It would seem to be attractive to support negotiation of bundle with the first offer/answer transaction else it will be delayed.  And some networks may not need a 2nd offer/answer if the first one successfully negotiates one of the options.