Re: [Ice] active / frozen check lists

[Taylor Brandstetter <[e-mail]>]

Trickle ICE doesn't need to use the "active"/"frozen" state any more. I
brought this up in my review of draft-08:
https://mailarchive.ietf.org/arch/msg/ice/eiAyekLr4aTvFoDzUGhK3gyIsmY

Also, the reference to section 5.1.4 is just slightly outdated; section
5.1.4 previously referred to the "active" state, and now it doesn't.

So I don't think we have a problem. I agree with Christer's points.

On Mon, Jul 24, 2017 at 9:27 AM, Peter Saint-Andre <[e-mail]>
wrote:

> On 7/24/17 9:11 AM, Christer Holmberg wrote:
> > Hi Peter,
> >
> > Thanks for your input! Please see inline.
> >
> >> Apparently it was decided at IETF 99 to remove the terms "active
> >> check list" and "frozen check list" from the core spec. These terms
> >> are used in the trickle spec. For example:
> >>
> >> ###
> >>
> >> A Trickle ICE agent initially considers all check lists to be
> >> frozen. It then inspects the first check list and attempts to
> >> unfreeze all candidate pairs it has received so far that belong to
> >>  the first component on the first media stream (i.e., the first
> >> media stream that was reported to the ICE implementation from the
> >> using application). If that first component of the first media
> >> stream does not contain candidates for one or more of the currently
> >> known pair foundations, and if candidate pairs already exist for
> >> that foundation in one of the following components or media
> >> streams, then the agent unfreezes the first of those candidate
> >> pairs.
> >
> > How would this change if we removed "frozen check list"?
>
> We'd probably need to create a circumlocation such as "considers all
> candidate pairs in all check lists to be frozen".
>
> > We obviously would have to remove the term also from trickle, but
> > would it affect the procedures?
>
> I don't think so, just the terminology and text.
>
> > ###
> >
> >> The ICE specification [rfc5245bis], Section 5.1.4, requires that an
> >> agent will terminate the timer for a triggered check in relation to
> >> an active check list once the agent has exhausted all frozen pairs
> >> in the check list. This will not work with Trickle ICE, because
> >> more pairs will be added to the check list incrementally.
> >
> > Do you refer to bullet 4) in section 5.1.4.2?
> >
> > It is true that the non-trickle agent will eventually cease checking
> > the check lists, but what does that have to do with the
> > "active/frozen check list" terms?
>
> Not much, I think. Later this week I will look at the text in detail.
>
> > ###
> >
> >> When a check list is set to Failed as described above, regular ICE
> >> requires the agent to update all other check lists, placing one
> >> pair from each check list into the Waiting >state - effectively
> >> unfreezing all remaining check lists. However, under Trickle ICE
> >> other check lists might still be empty at this point (because
> >> candidates have not yet been >received), and following only the
> >> rules from regular ICE would prevent the agent from unfreezing
> >> those check lists (because the state of a check list depends on the
> >> state of >the candidate pairs in that check list, but there are
> >> none yet). Therefore a Trickle ICE agent needs to monitor whether a
> >> check list is active or frozen independently of the >state of the
> >> candidate pairs in the check list (since there might not be any
> >> pairs yet). With regard to empty check lists, by default a Trickle
> >> ICE agent MAY consider an empty >check list to be either active or
> >> frozen. When a Trickle ICE agent considers an empty check list to
> >> be frozen, during the candidate checking process it SHOULD change
> >> the >check list to active if checking of another check list is
> >> completely finished (i.e., if every pair in the other check list is
> >> either Successful or Failed), if another check list has a >valid
> >> candidate pair for all components, or if it adds a candidate pair
> >> to the check list (because, in accordance with Section 8.1.1, when
> >> inserting a new candidate pair into an >empty check list, the agent
> >> sets the pair to a state of Waiting).
> >
> > Why would an agent need to consider an empty list active or frozen?
> > Can't the agent simply put the list in RUNNING state, even if it's
> > empty, and whenever Ta triggers for that list the agent will check
> > whether there are any candidates, and process them accordingly.
>
> I will look at this later this week, as well.
>
> > ###
> >
> >> If we decide to continue with this approach, we'll need to look
> >> more closely at the text in the trickle spec and make the necessary
> >> wording changes.
> >
> > Absolutely. But, based on your input, I don't identity any technical
> > changes. Or have I missed them?
>
> Agreed.
>
> Peter
>
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