Re: [rtcweb] New SDP O/A required if selected ICE candidate does not match c= line?

Iñaki,

in the past some thoughts were already presented that the updated SDP offer/answer exchange is not necessary in all environments.
See e.g. https://tools.ietf.org/html/draft-rosenberg-mmusic-ice-nonsip-01#section-5.4.2 as cited below:

“ICE defines conditions on which an updated offer is required to be sent after ICE concludes - namely, if the candidates selected by ICE are not a match for the default candidates, an updated exchange is sent.
This function of ICE is primarily an artifact of the realities of SIP deployments. It is not at all needed for correctness of ICE operation. In the case of SIP, signaling intermediaries that are inspecting the offer/answer exchanges, but are not ICE aware, will be confused unless there is an updated exchange. This same consideration applies to using protocols. If the using protocol has deployments with intermediaries that inspect messages, and will be confused if the actual connections/media are established to something different than any defaults that were signaled, the updated exchange should be used. If not, it can be avoided.”

I think that in a pure WebRTC environment the second O/A can be omitted. 

Regards
Thomas 

> -----Original Message-----
> From: rtcweb-bounces@ietf.org [mailto:rtcweb-bounces@ietf.org] On
> Behalf Of Iñaki Baz Castillo
> Sent: Donnerstag, 24. Oktober 2013 02:45
> To: rtcweb@ietf.org
> Subject: [rtcweb] New SDP O/A required if selected ICE candidate does
> not match c= line?
> 
> Hi, RFC 5245 (ICE) says:
> 
> -----------------------------
>   4.1.4.  Choosing Default Candidates
> 
>    A candidate is said to be default if it would be the target of media
>    from a non-ICE peer; that target is called the DEFAULT DESTINATION.
>    If the default candidates are not selected by the ICE algorithm when
>    communicating with an ICE-aware peer, an updated offer/answer will
> be
>    required after ICE processing completes in order to "fix up" the SDP
>    so that the default destination for media matches the candidates
>    selected by ICE.  If ICE happens to select the default candidates,
> no
>    updated offer/answer is required.
> ------------------------------
> 
> Having to perform a second SDP O/A just to "fix the c= line" seems
> terriblly annoying and unuseful IMHO. Said that, this is obviously
> "violated" by WebRTC browsers, right?
> 
> Thanks a lot.
> 
> 
> 
> --
> Iñaki Baz Castillo
> <ibc@aliax.net>
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