Re: [rtcweb] When are ICE candidates added to the SDP

Silvia Pfeiffer <silviapfeiffer1@gmail.com> Tue, 13 May 2014 07:55 UTC

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Date: Tue, 13 May 2014 17:54:54 +1000
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From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
To: "Rauschenbach, Uwe (NSN - DE/Munich)" <uwe.rauschenbach@nsn.com>
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Subject: Re: [rtcweb] When are ICE candidates added to the SDP
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On 13 May 2014 16:06, "Rauschenbach, Uwe (NSN - DE/Munich)" <
uwe.rauschenbach@nsn.com> wrote:
>
>
>
> > -----Original Message-----
> > From: ext Martin Thomson [mailto:martin.thomson@gmail.com]
> >
> > On 12 May 2014 20:46, Rauschenbach, Uwe (NSN - DE/Munich)
> > <uwe.rauschenbach@nsn.com> wrote:
> > >
> > > A question on step 6 and your statement below the sequence: What would
> > be the difference between an SDP created by pc.createOffer in step 6 and
> > one obtained by getting pc.localDescription in step 6?
> >
> > The difference is that the second contains candidates.
>
> Uwe: Then, let me elaborate a bit more.
>
> Obviously, we need an SDP reflecting the local configuration for two
purposes:
> 1) To feed it to setLocalDescription in order to start the ICE gathering
> 2) To send it as an offer to the other peer
>
> The name "createOffer" implies that the SDP delivered as the result of
createOffer is the one to use as an offer in negotiation. Looking at the
way this mechanism has evolved, this is probably only true anymore if one
is prepared to send the offer immediately, and then to trickle ICE
candidates. To obtain an SDP to use as an offer in negotiations without
trickle ICE, one has to call setLocal, wait for "end of candidates" and
then read pc.localDescription.
>
> So "createOffer" in fact does not create an offer, but an initial (or
updated) local description that is then fed into setLocalDescription to
start the ICE gathering.
>
> Do you agree with this observation? If you do, shouldn't we rename
createOffer to something more generic like "createLocalDescription" or
similar? "createOffer" does not create the offer (at least it does not do
so in case of non-trickling) but the input to setLocal...
>

I agree, the name is very misleading now.

Silvia.

>
> > > Why do you consider multiple pc.createOffer calls nasty?
> >
> > They aren't convenient.  You risk mistakes.
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