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

Iñaki Baz Castillo <ibc@aliax.net> Thu, 24 October 2013 10:56 UTC

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From: Iñaki Baz Castillo <ibc@aliax.net>
Date: Thu, 24 Oct 2013 12:56:08 +0200
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To: "Stach, Thomas" <thomas.stach@unify.com>
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Subject: Re: [rtcweb] New SDP O/A required if selected ICE candidate does not match c= line?
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2013/10/24 Stach, Thomas <thomas.stach@unify.com>:
> 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.


So, basically such a "SDP fix up" is 100% unnecesary for SIP endpoints
in the session, and just "useful" for intermediary servers to know
which media path is being used. IMHO RFC 5245 should NOT state that at
all.

Thanks a lot for the clarification.

-- 
Iñaki Baz Castillo
<ibc@aliax.net>

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