Re: [rtcweb] Replacing a=extmap mapping in re-offer, is it legal?

Hi,
Inline
Roni Even

> -----Original Message-----
> From: rtcweb [mailto:rtcweb-bounces@ietf.org] On Behalf Of Christer
> Holmberg
> Sent: יום ב 07 אוגוסט 2017 21:02
> To: Iñaki Baz Castillo; Taylor Brandstetter
> Cc: rtcweb@ietf.org
> Subject: Re: [rtcweb] Replacing a=extmap mapping in re-offer, is it legal?
> 
> Hi,
> 
> Taylor's explanation makes sense. But, in this case:
> 
> 1) Re-using the same value with a new mapping should be an explicit MUST
> NOT
[Roni Even] This is specified in RFC5285 section 6 

Identifiers values in the valid range MUST NOT  be altered (remapped).

> 
> 2) The re-offer should be rejected
> 
> Regards,
> 
> Christer
> 
> -----Original Message-----
> From: Iñaki Baz Castillo [mailto:ibc@aliax.net]
> Sent: 07 August 2017 19:56
> To: Taylor Brandstetter <deadbeef@google.com>
> Cc: Christer Holmberg <christer.holmberg@ericsson.com>; rtcweb@ietf.org
> Subject: Re: [rtcweb] Replacing a=extmap mapping in re-offer, is it legal?
> 
> On Mon, Aug 7, 2017 at 7:46 PM, Taylor Brandstetter
> <deadbeef@google.com> wrote:
> > I don't know if this is stated explicitly anywhere, but my assumption
> > was that it works like payload types. You can introduce new IDs all
> > you want, but you can't have one ID refer to multiple things during the
> same session.
> > Otherwise, if you receive a packet with that extension ID, you
> > wouldn't be able to tell which extension it is.
> >
> > Meaning, if Bob's initial answer was:
> >
> > a=extmap:11 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-
> time
> >
> > It would be illegal to have a re-offer of:
> >
> > a=extmap:1 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-
> time
> > a=extmap:11 urn:ietf:params:rtp-hdrext:toffset
> >
> > Because if Bob then receives a packet with extension ID 11, Bob
> > doesn't know if it's a packet sent before Alice received the answer
> > (in which case it's "abs-send-time"), or after (in which case it's "toffset").
> 
> Thanks, your rationale clearly makes sense. However:
> 
> 1) I don't think Firefox cares about overriding a previous extmap ID during a
> reoffer.
> 
> 2) Should we really accept so complex and error prune things just because
> SDP allows everything?
> 
> 
> --
> Iñaki Baz Castillo
> <ibc@aliax.net>
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