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

[Harald Alvestrand <[e-mail]>]

On 05/12/2014 05:17 PM, Eric Rescorla wrote:
>
>
>
> On Mon, May 12, 2014 at 6:51 AM, Harald Alvestrand 
> <[e-mail] <mailto:[e-mail]>> wrote:
>
>     On 05/12/2014 02:39 PM, Eric Rescorla wrote:
>>
>>
>>
>>     On Mon, May 12, 2014 at 2:03 AM, Rauschenbach, Uwe (NSN -
>>     DE/Munich) <[e-mail]
>>     <mailto:[e-mail]>> wrote:
>>
>>         Hi Eric, all,
>>
>>         Is the consequence of “always trickle” that ICE candidates
>>         have to be added by non-trickling applications via SDP
>>         manipulation?
>>
>>         I consider this indeed quite inconvenient for non-trickling
>>         applications.
>>
>>
>>     So, my understanding was that we had agreed that no candidates would
>>     be available in the first CreateOffer() no matter how many
>>     candidates were
>>     in the pool.
>>
>>     The intent of this message is to ask if that is useful.
>
>     If an application is written as
>
>     1) CreateOffer()
>     2) wait for the end of candidates callback
>     3) negotiate
>
>     then I would think it might have trouble if all the candidates are
>     present in the SDP, and therefore no callbacks were called.
>     Solution: Always fire the end of candidates callback after calling
>     the success callback, even if all candidates are in the SDP already.
>
>
> So you mean:
>
> 1. CreateOffer()
> 2. success callback fires.
> 3. SetLocal()
> 4. onicecandidate(...)
> 5. onicecandidate(null)
>
> Then later (w/ no changes to the MSTs)
>
> 6. CreateOffer()
> 7. success callback fires
> 8. SetLocal (????)
> 9. onicecandidate(null)
>
> I believe this would be a change to the W3C API (not that this is 
> necessarily bad)

Something like that, yes. Or in more detail, for a call requiring 2 
candidates:

1. CreateOffer()
2. success callback fires (1 candidate present)
3. SetLocal()
4. onicecandidate(...)
5. onicecandidate(null)

Then later (w/ no changes to the MSTs)

6. CreateOffer()
7. success callback fires (2 candidates present)
8. SetLocal ()
9. onicecandidate(null)

Then still later (after having done something that requires a 3rd 
candidate):

10. CreateOffer()
11. successCallback fires (2 candidates present)
12. SetLocal()
13. onicecandidate(...)
14. onicecandidate(null)

If we don't have the null onicecandidate in case 2 (step 9), it gets 
hard to support case 3 (step 12-14).

>
> -Ekr
>
>
>>
>>     -Ekr
>>
>>         A way out would be that the SDP always contains the
>>         candidates collected so far (as currently defined in the JSEP
>>         snippet cited),
>>
>>         or that a switch in the API allows an application to
>>         configure the behavior when adding ICE candidates.
>>
>>         Kind regards,
>>         Uwe
>>
>>         *From:*rtcweb [mailto:[e-mail]
>>         <mailto:[e-mail]>] *On Behalf Of *ext Eric
>>         Rescorla
>>         *Sent:* Monday, May 12, 2014 8:52 AM
>>         *To:* [e-mail] <mailto:[e-mail]>
>>         *Subject:* [rtcweb] When are ICE candidates added to the SDP
>>
>>         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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>>     [e-mail]  <mailto:[e-mail]>
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>
>
>     -- 
>     Surveillance is pervasive. Go Dark.
>
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