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

[Iñaki Baz Castillo <[e-mail]>]

On Mon, Aug 7, 2017 at 7:46 PM, Taylor Brandstetter <[e-mail]> 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
<[e-mail]>