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From: Eric Rescorla <ekr@rtfm.com>
Date: Sun, 11 May 2014 16:51:43 -0700
Message-ID: <CABcZeBNUTf42tS9FrjS9Q6Zk8LBkhpKOR1z2v8MHoeNEUf93Mw@mail.gmail.com>
To: "rtcweb@ietf.org" <rtcweb@ietf.org>
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Archived-At: http://mailarchive.ietf.org/arch/msg/rtcweb/uz7llD_kzlAmaVH3gfThrhC6S4Y
Subject: [rtcweb] When are ICE candidates added to the SDP
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See: https://github.com/rtcweb-wg/jsep/issues/11

Section 3.4 reads:

When a new ICE candidate is available, the ICE Agent will notify the
application via a callback; these candidates will automatically be
added to the local session description. When all candidates have
been gathered, the callback will also be invoked to signal that the
gathering process is complete.

However, we agreed in London that we would do "always trickle", and
that even if there were candidates available at the time when CreateOffer
(because of candidate pooling) was called, they would not be included
in the initial offer. Consider the following sequence of events.

0. pc = new RTCPeerConnection();
1. pc.AddStream(stream);
2. pc.CreateOffer();
3. CreateOffer callback fires with offer A, and you call
SetLocalDescription();
4. onicecandidate fires with candidate X.
5. pc.CreateOffer()
6. CreateOffer callback fires with offer B.
7. onicecandidate fires with null.

So, in London, I think we agreed that offer A would have no candidates.
The above text implies that if you were to examine localdescription prior
to step #5 or at step #7 it would contain candidate X, and probably that
offer B would
also contain candidate X.

Note that it's quite inconvenient for non-trickle applications to never
have any candidates in the SDP, especially after gathering is completed
at step #7. However it also seems kind of inconsistent to only update the
candidates after SetLocal() has been called.

-Ekr

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<div dir=3D"ltr">See: <a href=3D"https://github.com/rtcweb-wg/jsep/issues/1=
1">https://github.com/rtcweb-wg/jsep/issues/11</a><br><div><br></div><div><=
div>Section 3.4 reads:</div><div><br></div><div>When a new ICE candidate is=
 available, the ICE Agent will notify the</div>

<div>application via a callback; these candidates will automatically be</di=
v><div>added to the local session description. When all candidates have</di=
v><div>been gathered, the callback will also be invoked to signal that the<=
/div>

<div>gathering process is complete.</div><div><br></div><div>However, we ag=
reed in London that we would do &quot;always trickle&quot;, and</div><div>t=
hat even if there were candidates available at the time when CreateOffer</d=
iv>

<div>(because of candidate pooling) was called, they would not be included<=
/div><div>in the initial offer. Consider the following sequence of events.<=
/div><div><br></div><div>0. pc =3D new RTCPeerConnection();</div><div>1. pc=
.AddStream(stream);</div>

<div>2. pc.CreateOffer();</div><div>3. CreateOffer callback fires with offe=
r A, and you call SetLocalDescription();</div><div>4. onicecandidate fires =
with candidate X.</div><div>5. pc.CreateOffer()</div><div>6. CreateOffer ca=
llback fires with offer B.</div>

<div>7. onicecandidate fires with null.</div><div><br></div><div>So, in Lon=
don, I think we agreed that offer A would have no candidates.</div><div>The=
 above text implies that if you were to examine localdescription prior</div=
>

<div>to step #5 or at step #7 it would contain candidate X, and probably th=
at offer B would</div><div>also contain candidate X.</div><div><br></div><d=
iv>Note that it&#39;s quite inconvenient for non-trickle applications to ne=
ver</div>

<div>have any candidates in the SDP, especially after gathering is complete=
d</div><div>at step #7. However it also seems kind of inconsistent to only =
update the</div><div>candidates after SetLocal() has been called.</div>

</div><div><br></div><div>-Ekr</div><div><br></div></div>

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