Re: [Ice] Re-nomination and candidate pair switching in RFC 5245bis

Peter said:

"Your reasoning for saying that an agent can't switch candidate pairs is
that it prevents the remote side from being able to release resources.  But
the switching side would only switch if the candidate pair recently
received an ICE check response (in other words, it knows the candidate pair
works), in which case it knows that resources have not been released."

[BA] There is a dicotomy between the situation prior to nomination and
after it that isn't explained well in RFC 5245bis.  Prior to nomination,
the agent can switch between validated candidate pairs, and hopefully we
can make the language clear enough so that this will work well.

While the same logic applies after nomination as well (e.g. it only makes
sense to switch a valid pair), the text doesn't clarify the meaning of
nomination with respect to resource release, nor does it talk about consent
(presumably the mechanism that would be used to maintain pair validity
after nomination), so that it's not clear how pair validity could be
maintained.  Since there is much RFC 5245 text still remaining, the overall
document reads as though while it represents an update to RFC 5245 it still
is based on a pre-WebRTC mindset.

All this makes me wonder whether we should limit our aspirations for RFC
5245bis to clarifying things "just enough" so that it isn't a hindrance.
People interested in building a modern ICE implementation for use in WebRTC
will probably focus more on Trickle-ICE, where implementation of consent
can be assumed, and perhaps the meaning of nomination within a WebRTC
context could be better explained.

On Wed, Aug 30, 2017 at 11:19 AM, Peter Thatcher <pthatcher@google.com>
wrote:

> #2 and #3 are fine, but I'm not a fan of #1.
>
> Your reasoning for saying that an agent can't switch candidate pairs is
> that it prevents the remote side from being able to release resources.  But
> the switching side would only switch if the candidate pair recently
> received an ICE check response (in other words, it knows the candidate pair
> works), in which case it knows that resources have not been released.
>
> In other words, if the remote side chose to release resources, the local
> side wouldn't do the switch.  So the remote side is free to release
> resources; it's not prevented from doing so.  If it does, then the local
> side will notice and not do a switch.   But if the remote side doesn't
> release the resources, then the local side may switch.
>
> In other words, I think we can allow switching and resource release both.
>
> On Thu, Jul 27, 2017 at 4:01 AM Christer Holmberg <
> christer.holmberg@ericsson.com> wrote:
>
>> Hi,
>>
>>
>>
>> Would anyone disagree with the following:
>>
>>
>>
>> 1)      explicitly indicating that re-nomination is **NOT** allowed
>> without ICE restart; and
>>
>> 2)      once a pair has been selected, agents need to be able to send *
>> *AND** receive media using that pair – but not using any other pair
>> (read: resources associated with other pairs may be released); and
>>
>> 3)      PRIOR to selection, agents need to be able to send **AND**
>> receive media on any valid pair (RFC 7675 adds restrictions, but that’s
>> outside the scope of 5245bis)
>>
>>
>>
>> Regards,
>>
>>
>>
>> Christer
>>
>>
>>
>> *From:* Ice [mailto:ice-bounces@ietf.org] *On Behalf Of *Christer
>> Holmberg
>> *Sent:* 25 July 2017 10:17
>> *To:* Bernard Aboba <bernard.aboba@gmail.com>
>> *Cc:* ice@ietf.org
>> *Subject:* Re: [Ice] Re-nomination and candidate pair switching in RFC
>> 5245bis
>>
>>
>>
>> Hi Bernard,
>>
>>
>>
>> Regarding sending media PRIOR to nomination, we have previously agreed
>> that any valid pair can be used for that. Perhaps it needs more
>> clarification.
>>
>>
>>
>> Regarding receiving media after nomination, it was discussed in Prague,
>> as it is covered by Peter’s PR. I don’t have access to the PR/minutes right
>> now, but I think the outcome was that an agent is only expected to receive
>> media on the nominated pair (otherwise it cannot free resources).
>>
>>
>>
>> Regards,
>>
>>
>>
>> Christer
>>
>>
>>
>> *From:* Bernard Aboba [mailto:bernard.aboba@gmail.com
>> <bernard.aboba@gmail.com>]
>> *Sent:* 25 July 2017 02:29
>> *To:* Christer Holmberg <christer.holmberg@ericsson.com>
>> *Cc:* ice@ietf.org
>> *Subject:* Re: [Ice] Re-nomination and candidate pair switching in RFC
>> 5245bis
>>
>>
>>
>> Christer said:
>>
>>
>>
>> "The whole discussion began when I was given a comment that the text
>> above should be modified, to clarify that the pair used for media can
>> change after a pair has been selected.
>>
>> But, if the outcome is that the pair can NOT change, maybe we need to
>> clarify THAT instead :)"
>>
>>
>>
>> [BA] Currently, use of the "ice2" ICE option forestalls use of aggressive
>> nomination (e.g. setting the nominated flag on more than one pair).  Since
>> only the selected pair can be used to send media, that would seem to rule
>> out changing the pair used for media after a pair has been selected:
>>
>>
>>
>>    Once a candidate pair has been selected
>>
>>    only that candidate pair (referred to as selected pair) is used for
>>
>>    sending media.
>>
>>
>>
>> What about changing the pair used for media prior to selection?  On this
>> point, the text seems less clear than it could be.
>>
>>
>>
>> Prior to nomination, the specification allows the sending of media on a
>> successful pair:
>>
>>
>>
>>    o  Once there is at least one nominated pair in the VALID LIST for
>>
>>       every component of at least one media stream and the state of the
>>
>>       CHECK LIST is Running:
>>
>>
>>
>> ...
>>
>>
>>
>>       *  The agent MUST continue to respond to any checks it may still
>>
>>          receive for that media stream, and MUST perform triggered
>>
>>          checks if required by the processing of Section 6.3 <https://tools.ietf.org/html/draft-ietf-ice-rfc5245bis-10#section-6.3>.
>>
>>
>>
>>       *  The agent MAY begin transmitting media for this media stream as
>>
>>          described in Section 11.1
>> <https://tools.ietf.org/html/draft-ietf-ice-rfc5245bis-10#section-11.1>.
>>
>>
>>
>> However, the specification is not clear enough about the receiving side;
>> while it recommends that implementations be prepared to receive prior to
>> nomination, it does not require this. From Section 11.2:
>>
>>
>>
>>    ICE implementations SHOULD by default be
>>
>>    prepared to receive media on any of the candidates provided in the
>>
>>    most recent candidate exchange with the peer.
>>
>>
>>
>> What happens if an implementation is NOT prepared to receive media?
>>
>> In WebRTC, an implementation cannot send without consent, which
>>
>> suggests that perhaps an unwilling receiver could use consent to
>>
>> influence the potential sender.
>>
>>
>>
>> However, the specification does not even reference RFC 7675,
>>
>> so it is left unclear about how this is to be done.
>>
>> For example, a receiver might not reply to a consent
>>
>> request if the inability to receive is temporary ("I'm not ready yet"),
>>
>> but that might cause consent to time out prior to nomination and
>>
>> might even influence pair selection inappropriately.
>>
>>
>>
>> Another choice might be to revoke consent (which would
>>
>> invalidate the pair).  But that's pretty drastic unless the
>>
>> pair is truly unacceptable.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> >[BA] RFC 5245bis Section 7.1.1 continues to imply a single selected
>> pair:
>> >
>> >   Eventually, there will be only a single nominated pair in the VALID
>> >   LIST for each component.  Once the state of the CHECK LIST is set to
>> >   Completed, that exact pair is selected by ICE for sending and
>> >   receiving media for that component.
>> >
>> >Based on that text, an implementation might still release resources
>> (e.g. unused TURN candidates) post-nomination. Given this, the "ice2" ICE
>> option doesn't address >potential interoperability issues resulting from
>> different resource release behaviors (although it does clear indicate lack
>> of support for aggressive nomination):
>>
>> The whole discussion began when I was given a comment that the text above
>> should be modified, to clarify that the pair used for media can change
>> after a pair has been selected.
>>
>> But, if the outcome is that the pair can NOT change, maybe we need to
>> clarify THAT instead :)
>>
>> >   NOTE: A controlling agent that does not support this specification
>> >   (i.e. it is implemented according to RFC 5245) might nominate more
>> >   than one candidate pair.  This was referred to as aggressive
>> >   nomination in RFC 5245.  The usage of the 'ice2' ice option by
>> >   endpoints supporting this specifcation should prevent such
>> >   controlling agents from using aggressive nomination.
>> >
>> >Christer also said:
>> >
>> >"Also, my understanding was that endpoints supporting RFC 7675 might
>> maintain consent on pairs currently not
>> >used for media, in order to be able to re-nominate in case consent for
>> the currently nominated pair expires. However,
>> >RFC 7675 does not explicitly say anything about that."
>> >
>> >[BA] RFC 7675 Section 5 says:
>> >
>> >   Initial consent to send traffic is obtained using ICE [RFC5245].  An
>> >   endpoint gains consent to send on a candidate pair when the pair
>> >   enters the Succeeded ICE state.
>> >
>> >Given this, an RFC 5245bis implementation might request consent to send
>> to
>> >multiple remote peer candidates, so as to keep them alive. However,
>> >there is nothing in RFC 7675 that requires the responder to grant
>> >consent for that.  For example, based on the text in RFC 5245bis
>> >Section 7.1.1, a conforming implementation might well revoke
>> >consent on local candidates other than the local candidate in the
>> >selected pair.
>>
>> Sure - the responder is not mandated to grant consent to multiple
>> candidates after nomination. But, the option to do seems to be there
>> (unless I've understood the RFC wrong), and the only reason to do so would
>> be possible re-nomination.
>>
>> Anyway, I don't have any strong feelings which way we go, but we do need
>> to make it clear in the spec whether re-nomination is allowed or not.
>>
>> Regards,
>>
>> Christer
>>
>>
>>
>> On Mon, Jul 24, 2017 at 4:33 PM, Christer Holmberg <
>> christer.holmberg@ericsson.com> wrote:
>>
>> Hi
>> ,
>> >[BA] RFC 5245bis Section 7.1.1 continues to imply a single selected
>> pair:
>> >
>> >   Eventually, there will be only a single nominated pair in the VALID
>> >   LIST for each component.  Once the state of the CHECK LIST is set to
>> >   Completed, that exact pair is selected by ICE for sending and
>> >   receiving media for that component.
>> >
>> >Based on that text, an implementation might still release resources
>> (e.g. unused TURN candidates) post-nomination. Given this, the "ice2" ICE
>> option doesn't address >potential interoperability issues resulting from
>> different resource release behaviors (although it does clear indicate lack
>> of support for aggressive nomination):
>>
>> The whole discussion began when I was given a comment that the text above
>> should be modified, to clarify that the pair used for media can change
>> after a pair has been selected.
>>
>> But, if the outcome is that the pair can NOT change, maybe we need to
>> clarify THAT instead :)
>>
>> >   NOTE: A controlling agent that does not support this specification
>> >   (i.e. it is implemented according to RFC 5245) might nominate more
>> >   than one candidate pair.  This was referred to as aggressive
>> >   nomination in RFC 5245.  The usage of the 'ice2' ice option by
>> >   endpoints supporting this specifcation should prevent such
>> >   controlling agents from using aggressive nomination.
>> >
>> >Christer also said:
>> >
>> >"Also, my understanding was that endpoints supporting RFC 7675 might
>> maintain consent on pairs currently not
>> >used for media, in order to be able to re-nominate in case consent for
>> the currently nominated pair expires. However,
>> >RFC 7675 does not explicitly say anything about that."
>> >
>> >[BA] RFC 7675 Section 5 says:
>> >
>> >   Initial consent to send traffic is obtained using ICE [RFC5245].  An
>> >   endpoint gains consent to send on a candidate pair when the pair
>> >   enters the Succeeded ICE state.
>> >
>> >Given this, an RFC 5245bis implementation might request consent to send
>> to
>> >multiple remote peer candidates, so as to keep them alive. However,
>> >there is nothing in RFC 7675 that requires the responder to grant
>> >consent for that.  For example, based on the text in RFC 5245bis
>> >Section 7.1.1, a conforming implementation might well revoke
>> >consent on local candidates other than the local candidate in the
>> >selected pair.
>>
>> Sure - the responder is not mandated to grant consent to multiple
>> candidates after nomination. But, the option to do seems to be there
>> (unless I've understood the RFC wrong), and the only reason to do so would
>> be possible re-nomination.
>>
>> Anyway, I don't have any strong feelings which way we go, but we do need
>> to make it clear in the spec whether re-nomination is allowed or not.
>>
>> Regards,
>>
>> Christer
>>
>>
>>
>>
>>
>> On Fri, Jul 21, 2017 at 12:33 PM, Christer Holmberg <
>> christer.holmberg@ericsson.com> wrote:
>> Hi Bernard,
>>
>> Support of 5245bis is also negotiated, using the “ice2” ICE option.
>>
>> Also, my understanding was that endpoints supporting RFC 7675 might
>> maintain consent on pairs currently not used for media, in order to be able
>> to re-nominate in case consent for the currently nominated pair expires.
>> However, RFC 7675 does not explicitly say anything about that.
>>
>> Regards,
>>
>> Christer
>>
>> From: Ice [mailto:ice-bounces@ietf.org] On Behalf Of Bernard Aboba
>> Sent: 20 July 2017 14:22
>> To: ice@ietf.org
>> Subject: [Ice] Re-nomination and candidate pair switching in RFC 5245bis
>>
>> During the ICE WG meeting today, there was discussion of whether
>> RFC5245bis should indicate that it is possible to re-nominate pairs
>> (proposed by Peter), or whether it is possible to switch from one interface
>> to another (Cullen).  While these capabilities are desirable, attempting to
>> add them to RFC 5245bis without negotiation has the potential to break
>> interoperability with existing RFC 5245 implementations.
>>
>> In my experience, this is an area where RFC 5245 implementations have
>> very different interpretations. For example, some implementations (e.g.
>> ones that did not support aggressive) discard non-selected candidate pairs
>> after nomination. These implementations (e.g. particularly ones included in
>> previous product releases) cannot be assumed to change their behavior after
>> RFC 5245bis is published.  This raises the possibility that that
>> interoperability could be impacted.
>>
>> Since in practice the desired candidate pair switching capabilities are
>> most likely to be supported in WebRTC implementations supporting Trickle
>> ICE, my recommendation is to think of candidate pair switching as a Trickle
>> ICE capability.   Since Trickle-ICE support is negotiated, clarifications
>> relating to candidate-pair switching can be linked to that negotiation.
>>
>> This provides a potential way forward that bypasses potential
>> interoperability issues.  For example, if text on candidate-pair switching
>> is to be added to (either to RFC 5245bis or Trickle-ICE) then the text
>> could say that support for these behaviors can only be assumed if they are
>> explicitly negotiated. The Trickle-ICE document could then create normative
>> requirements for support of the new behaviors by stating that support for
>> them is mandatory when supporting full-Trickle.
>>
>>
>>
>>
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>>
>

Re: [Ice] Re-nomination and candidate pair switching in RFC 5245bis - PROPOSAL