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

From: Roni Even <[email-masked]>
Date: Wed, 9 Aug 2017 13:43:29 +0000

Hi Christer,
Inline, cc avtcore since it is avtcore document .
Look at https://tools.ietf.org/html/draft-ietf-avtcore-rfc5285-bis-14#section-7 
Roni

> -----Original Message-----
> From: Christer Holmberg [mailto:[email-masked]]
> Sent: יום ד 09 אוגוסט 2017 15:27
> To: Roni Even; Iñaki Baz Castillo; Taylor Brandstetter
> Cc: [email-masked]
> 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).
> 
> Correct. Taylor indicated this earlier.
> 
> What if a previously negotiated mapping is not included at all in a subsequent
> offer?

[Roni Even] It is removed not supported "A session update MAY add or  remove extension(s)."

 Is it considered an error?

[Roni Even] no

 If not, does the previous mapping apply? 
[Roni Even] if you want to use it you can consider making it inactive

Or,
> is the previous mapping removed?
[Roni Even] removed but you cannot use the same ID for another extension

> 
> Regards,
> 
> Christer
> 
> 
> 
> > From: Iñaki Baz Castillo [mailto:[email-masked]]
> > Sent: 07 August 2017 19:56
> > To: Taylor Brandstetter <[email-masked]>
> > Cc: Christer Holmberg <[email-masked]>;
> > [email-masked]
> > Subject: Re: [rtcweb] Replacing a=extmap mapping in re-offer, is it legal?
> >
> > On Mon, Aug 7, 2017 at 7:46 PM, Taylor Brandstetter
> > <[email-masked]> 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
> > <[email-masked]>
> > _______________________________________________
> > rtcweb mailing list
> > [email-masked]
> > https://www.ietf.org/mailman/listinfo/rtcweb