Re: [Ice] ICE PAC: When to start the timer waiting for possible peer reflexive candidates? - discussion restart

Justin Uberti <juberti@google.com> Wed, 10 July 2019 23:09 UTC

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References: <AFCE8799-8865-454F-8478-81CE11E9B454@ericsson.com> <1aa5aac7-af59-4e3b-8651-18f6e6431a2d@alvestrand.no> <66678ADA-7C02-4D9D-B9D2-308873BC0125@ericsson.com> <7a829bc0-d066-a3be-b7be-9b39ce799821@alvestrand.no> <CAJrXDUHZJURLvzBYX2MGcMsrFgyOagW5=s1OSXwDmTZpsruD0A@mail.gmail.com> <VI1PR07MB3167F21EF7A1009B8EB9948B93FB0@VI1PR07MB3167.eurprd07.prod.outlook.com> <CAOJ7v-11EjJK644RCb=nASVu_vwkhOxzj4XY4JUBW+1Fr19yOA@mail.gmail.com>
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From: Justin Uberti <juberti@google.com>
Date: Wed, 10 Jul 2019 16:09:11 -0700
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To: Christer Holmberg <christer.holmberg@ericsson.com>
Cc: Peter Thatcher <pthatcher@google.com>, Harald Alvestrand <harald@alvestrand.no>, Nils Ohlmeier <nohlmeier@mozilla.com>, Roman Shpount <roman@telurix.com>, "ice@ietf.org" <ice@ietf.org>
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Subject: Re: [Ice] ICE PAC: When to start the timer waiting for possible peer reflexive candidates? - discussion restart
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When writing up this text, I realized there are edge cases where you might
want to discover prflx candidates even if you didn't send any candidates
(e.g., you don't send any candidates, you get a single IP from the remote
side, and when you check it, you get a response back from a different IP).

Ergo, I think we should start the timer as soon as we have local and remote
ICE credentials, regardless of whether or not we send a candidate.

On Wed, Jul 3, 2019 at 9:22 PM Justin Uberti <juberti@google.com> wrote:

> For #1, I don't think the proposed solution is correct. The "alternative
> c)" that I proposed is to "Start the timer as soon as we have received a
> remote offer or answer and have also sent a local candidate to the remote
> side", which is different than what is mentioned in the OP.
>
> The rationale for this is:
> A) we can't start ICE processing (checks) until we get a remote
> offer/answer with ICE credentials
> B) we can't receive an incoming check that could create a prflx candidate
> unless we sent a candidate to the remote side
>
> Tracking this issue in https://github.com/cdh4u/draft-ice-pac/issues/12.
>
> For #2, I agree we should use the "max duration of a connectivity check
> transaction". I think this value will work just fine in real world
> scenarios. And if the timer expires before we have tested all pairs (this
> can certainly happen, in the case of two hosts with no connectivity to each
> other), we just resume existing ICE processing, and fail when everything
> moves to the failed state (i.e., every pair has timed out). The timer is
> simply there to prevent premature failures.
>
> Tracking in https://github.com/cdh4u/draft-ice-pac/issues/13
>
>
> On Wed, Jul 3, 2019 at 1:02 PM Christer Holmberg <
> christer.holmberg@ericsson.com> wrote:
>
>> So, what timer value do people want?
>>
>>
>>
>> And, assuming the timer value is not going to be based on the number of
>> streams, what do we do if the timer expires before we have tested all pairs
>> for all streams? I think we need to specify that.
>>
>>
>>
>> Regards,
>>
>>
>>
>> Christer
>>
>>
>>
>> *From:* Peter Thatcher <pthatcher@google.com>
>> *Sent:* 02 July 2019 03:56
>> *To:* Harald Alvestrand <harald@alvestrand.no>
>> *Cc:* Christer Holmberg <christer.holmberg@ericsson.com>; Justin Uberti <
>> juberti@google.com>; Nils Ohlmeier <nohlmeier@mozilla.com>; Roman
>> Shpount <roman@telurix.com>; ice@ietf.org
>> *Subject:* Re: [Ice] ICE PAC: When to start the timer waiting for
>> possible peer reflexive candidates? - discussion restart
>>
>>
>>
>> I agree.  The options you present seem reasonable and I think we should
>> move ahead with them.
>>
>>
>>
>> On Mon, Jun 24, 2019 at 6:20 AM Harald Alvestrand <harald@alvestrand.no>
>> wrote:
>>
>> On 6/24/19 12:06 PM, Christer Holmberg wrote:
>>
>> Hi,
>>
>>
>>
>> Go for what? 😊
>>
>> I was noting the month of silence, and thinking that I should encoruage a
>> decision to be taken - "analysis paralysis" is not a good thing!
>>
>>
>>
>> Regarding 1), eventhough it’s not my personal preference to start the
>> timer when the first offer/answer is sent, I could live with it.
>>
>>
>>
>> It's a well defined time, and is observable by the entity that has to act
>> when the timer expires, so I think it is much better than "undefined".
>>
>> That's my requirement :-)
>>
>>
>>
>>
>>
>> Regarding 2), however, I would really like some input on whether the
>> duration should be independent of the number of streams, components etc.
>>
>> I think having a single number is preferable to having a complex number
>> that could change over time (for instance, if we don't reset the timer when
>> adding streams, then adding or removing streams after the timer started
>> will lead to hard-to-define behavior).
>>
>>
>>
>> But my main concern is that we get this stuff done and get the basic
>> timer mechanism into interoperable code - having a spec to implement from
>> now is better than having a spec that has had slightly more discussion, but
>> no fundamental changes, 6 months from now.
>>
>>
>>
>>
>>
>> Regards,
>>
>>
>>
>> Christer
>>
>>
>>
>> *From: *Harald Alvestrand <harald@alvestrand.no> <harald@alvestrand.no>
>> *Date: *Sunday, 23 June 2019 at 9.08
>> *To: *Christer Holmberg <christer.holmberg@ericsson.com>
>> <christer.holmberg@ericsson.com>, Justin Uberti <juberti@google.com>
>> <juberti@google.com>, Nils Ohlmeier <nohlmeier@mozilla.com>
>> <nohlmeier@mozilla.com>
>> *Cc: *Roman Shpount <roman@telurix.com> <roman@telurix.com>,
>> "ice@ietf.org" <ice@ietf.org> <ice@ietf.org> <ice@ietf.org>
>> *Subject: *Re: [Ice] ICE PAC: When to start the timer waiting for
>> possible peer reflexive candidates? - discussion restart
>>
>>
>>
>> On 5/28/19 1:54 PM, Christer Holmberg wrote:
>>
>> Hi,
>>
>>
>>
>> We need to move forward with this.
>>
>>
>>
>> There are two main questions at the moment:
>>
>>
>>
>>    1. When does an endpoint start the timer ("minimum-time-to-run-ICE"
>>    timer, based on previous discussions)?
>>    2. What is the duration of the timer?
>>
>>
>>
>> Regarding 1), my understanding is that people suggest alternative c),
>> which starts the timer when an endpoint has sent (in an offer or answer) at
>> least one local candidate (or EOC).
>>
>>
>>
>>
>>
>> Regarding 2), it has been suggested that the duration would be the same
>> as the max duration of a connectivity check transaction. Do we think that
>> is enough, no matter how many media streams and components are used?
>>
>>
>>
>> Go for it. It is much better than having nothing.
>>
>>
>>
>>
>>
>> Regards,
>>
>>
>>
>> Christer
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> *From: *Ice <ice-bounces@ietf.org> <ice-bounces@ietf.org> on behalf of
>> Christer Holmberg <christer.holmberg@ericsson.com>
>> <christer.holmberg@ericsson.com>
>> *Date: *Friday, 3 May 2019 at 15.02
>> *To: *Justin Uberti <juberti@google.com> <juberti@google.com>, Nils
>> Ohlmeier <nohlmeier@mozilla.com> <nohlmeier@mozilla.com>
>> *Cc: *Roman Shpount <roman@telurix.com> <roman@telurix.com>,
>> "ice@ietf.org" <ice@ietf.org> <ice@ietf.org> <ice@ietf.org>
>> *Subject: *Re: [Ice] ICE PAC: When to start the timer waiting for
>> possible peer reflexive candidates?
>>
>>
>>
>> Hi,
>>
>>
>>
>> I don’t think there will be any interoperability issues. At the end of
>> the day PAC is only about how long to wait for candidates, so the worse
>> thing that can happen is than an agent declares ICE failure too early.
>>
>>
>>
>> And, no matter whether an agent knows that the peer supports PAC or not,
>>  it should aim at sending it’s candidates to its peer as soon as possible,
>> depending on whatever local policies. The agent should not delay sending
>> candidates just because it assumes that the peer will anyway wait for them.
>>
>>
>>
>> Regards,
>>
>>
>>
>> Christer
>>
>>
>>
>> *From: *Justin Uberti <juberti@google.com> <juberti@google.com>
>> *Date: *Thursday, 2 May 2019 at 22.28
>> *To: *Nils Ohlmeier <nohlmeier@mozilla.com> <nohlmeier@mozilla.com>
>> *Cc: *Christer Holmberg <christer.holmberg@ericsson.com>
>> <christer.holmberg@ericsson.com>, Roman Shpount <roman@telurix.com>
>> <roman@telurix.com>, "ice@ietf.org" <ice@ietf.org> <ice@ietf.org>
>> <ice@ietf.org>
>> *Subject: *Re: [Ice] ICE PAC: When to start the timer waiting for
>> possible peer reflexive candidates?
>>
>>
>>
>>
>>
>>
>>
>> On Thu, May 2, 2019 at 12:22 PM Nils Ohlmeier <nohlmeier@mozilla.com>
>> wrote:
>>
>>
>>
>>
>>
>>
>> On May 2, 2019, at 12:13, Justin Uberti <juberti@google.com> wrote:
>>
>>
>>
>>
>>
>>
>>
>> On Thu, May 2, 2019 at 10:07 AM Nils Ohlmeier <nohlmeier@mozilla.com>
>> wrote:
>>
>>
>> >> I do think Nils' point is important though, i.e., if we have a bad
>> server it will take a very long time to decide on 'last set of candidates',
>> >> which is probably not helpful. As such I think the potential positions
>> we can take are:
>> >> a) Start the timer as soon as we have an answer, regardless of any
>> candidates.
>> >> b) a) + receipt of at least one remote candidate (or remote EOC).
>> (This is Nils' suggestion).
>> >> c) a) + sending at least one local candidate (or local EOC).
>>
>> As we are mostly concerned about the remote side: 1) not providing us
>> with candidates, or 2) providing us with unusable candidates or 3)
>> providing us with candidates really late I don’t see how option c) would
>> help in any of these scenarios.
>> From my point of view we should choose either a) or b).
>>
>>
>>
>> c) is just a clarification of a), in that you can't expect to receive
>> prflx candidates until you've at least provided the other side with a
>> candidate, so that may be the right time for the timer to start. I don't
>> feel super strongly about this though.
>>
>>
>>
>> Ok. I hadn’t looked at it from that angle. So c) being a stronger a) I
>> guess it would be okay.
>>
>>
>>
>> I guess my only concern is that in Firefox we stopped doing a) because it
>> caused to many problems. With that in mind would it cause interop problems
>> if we leave up to the implementor to choose to implement either b) or c)?
>>
>>
>>
>> I'd be fine with that, but I'd want to describe what to watch out for.
>> Can you explain a bit more?
>>
>>
>>
>>
>>
>> >> b) has a problem if the remote side doesn't send any candidates, which
>> we want to explicitly allow.
>> >
>> > True.
>>
>> Just to make sure we are all on the same page: b) is only a problem in
>> the scenario where the remote side doesn’t send any candidates but also
>> does not send EOC.
>>
>>
>> The EOC should allow agents which explicitly don’t want to provide
>> candidate to get the timer started soon.
>> I think that leaves us with scenarios where the remote doesn’t provide
>> host candidates, and it’s reflexive or relay candidates take for ever
>> because of slow servers.
>>
>>
>>
>> Correct, but we can't control which endpoints will send us an EOC or not.
>> So that will always be a possibility.
>>
>>
>>
>> Fair enough.
>>
>>
>>
>>
>>
>> >> I tend to lean towards a) as the simplest option.
>> >
>> > Keep in mind that RFC 8445 is generic, so we need to to define what we
>> mean by "answer". I guess it means some kind of indication that makes the
>> agent assume that the remote peer has been contacted. In ice-sip-sdp we can
>> then map that to an SDP answer.
>>
>> Good point. We basically treat the SDP answer here to be something like
>> an beginning of ICE, because we don’t have an explicit signal for that. I
>> think in SDP based worlds there is no need for an extra signal like that.
>> Not sure if other use cases of ICE would benefit from an explicit begin
>> signal.
>>
>>
>>
>> The answer in some ways is an explicit begin signal, because it contains
>> the username/password information needed to start ICE checks.
>>
>>
>>
>> Yeah I didn’t see your reply before hitting send on mine. Using the
>> availability sounds like a good idea as the minimum gating function/signal.
>>
>>
>>
>> Best
>>
>>   Nils
>>
>>
>>
>>
>>
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>>
>> --
>>
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>>
>>
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