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Versions: (draft-ietf-mmusic-trickle-ice) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 Draft is active
In: IESG-wait
Network Working Group                                            E. Ivov
Internet-Draft                                                 Atlassian
Intended status: Standards Track                             E. Rescorla
Expires: August 26, 2017                                      RTFM, Inc.
                                                               J. Uberti
                                                                  Google
                                                          P. Saint-Andre
                                                                Filament
                                                       February 22, 2017


Trickle ICE: Incremental Provisioning of Candidates for the Interactive
               Connectivity Establishment (ICE) Protocol
                       draft-ietf-ice-trickle-06

Abstract

   This document describes "Trickle ICE", an extension to the
   Interactive Connectivity Establishment (ICE) protocol that enables
   ICE agents to send and receive candidates incrementally rather than
   exchanging complete lists.  With such incremental provisioning, ICE
   agents can begin connectivity checks while they are still gathering
   candidates and considerably shorten the time necessary for ICE
   processing to complete.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 26, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Determining Support for Trickle ICE . . . . . . . . . . . . .   5
   4.  Sending the Initial ICE Description . . . . . . . . . . . . .   6
   5.  Receiving the Initial ICE Description . . . . . . . . . . . .   7
     5.1.  Sending the Initial Response  . . . . . . . . . . . . . .   7
     5.2.  Forming Check Lists and Beginning Connectivity
           Checks  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Receiving the Initial Answer  . . . . . . . . . . . . . . . .   8
   7.  Performing Connectivity Checks  . . . . . . . . . . . . . . .   8
     7.1.  Scheduling Checks . . . . . . . . . . . . . . . . . . . .   8
     7.2.  Check List and Timer State Updates  . . . . . . . . . . .   9
   8.  Discovering and Sending Additional Local Candidates . . . . .   9
     8.1.  Pairing Newly Learned Candidates and Updating
           Check Lists . . . . . . . . . . . . . . . . . . . . . . .  11
       8.1.1.  Inserting a New Pair in a Check List  . . . . . . . .  12
     8.2.  Announcing End of Candidates  . . . . . . . . . . . . . .  13
   9.  Receiving Additional Remote Candidates  . . . . . . . . . . .  14
   10. Receiving an End-Of-Candidates Notification . . . . . . . . .  15
   11. Trickle ICE and Peer Reflexive Candidates . . . . . . . . . .  15
   12. Concluding ICE Processing . . . . . . . . . . . . . . . . . .  15
   13. Subsequent Exchanges  . . . . . . . . . . . . . . . . . . . .  15
   14. Unilateral Use of Trickle ICE (Half Trickle)  . . . . . . . .  16
   15. Requirements for Signaling Protocols  . . . . . . . . . . . .  17
   16. Example Flow  . . . . . . . . . . . . . . . . . . . . . . . .  17
   17. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   18. Security Considerations . . . . . . . . . . . . . . . . . . .  18
   19. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  18
   20. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     20.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     20.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Appendix A.  Interaction with Regular ICE . . . . . . . . . . . .  20
   Appendix B.  Interaction with ICE Lite  . . . . . . . . . . . . .  21
   Appendix C.  Preserving Candidate Order while Trickling . . . . .  22
   Appendix D.  Changes from Earlier Versions  . . . . . . . . . . .  23
     D.1.  Changes from draft-ietf-ice-trickle-04  . . . . . . . . .  23



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     D.2.  Changes from draft-ietf-ice-trickle-03  . . . . . . . . .  24
     D.3.  Changes from draft-ietf-ice-trickle-03  . . . . . . . . .  24
     D.4.  Changes from draft-ietf-ice-trickle-02  . . . . . . . . .  24
     D.5.  Changes from draft-ietf-ice-trickle-01  . . . . . . . . .  24
     D.6.  Changes from draft-ietf-ice-trickle-00  . . . . . . . . .  24
     D.7.  Changes from draft-mmusic-trickle-ice-02  . . . . . . . .  24
     D.8.  Changes from draft-ivov-01 and draft-mmusic-00  . . . . .  25
     D.9.  Changes from draft-ivov-00  . . . . . . . . . . . . . . .  25
     D.10. Changes from draft-rescorla-01  . . . . . . . . . . . . .  26
     D.11. Changes from draft-rescorla-00  . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Introduction

   The Interactive Connectivity Establishment (ICE) protocol
   [rfc5245bis] describes mechanisms for gathering candidates,
   prioritizing them, choosing default ones, exchanging them with a
   remote party, pairing them, and ordering them into check lists.  Once
   all of these actions have been completed (and only then), the parties
   can begin a phase of connectivity checks and eventually select the
   pair of candidates that will be used in a media session or for a
   given media stream.

   Although the sequence described above has the advantage of being
   relatively straightforward to implement and debug once deployed, it
   can also be rather lengthy.  Candidate gathering often involves
   things like querying STUN [RFC5389] servers and allocating relayed
   candidates at TURN [RFC5766] servers.  All of these actions can be
   delayed for a noticeable amount of time; although they can be run in
   parallel, they still need to respect the pacing requirements from
   [rfc5245bis], which is likely to delay them even further.  Some or
   all of these actions also need be completed by the remote agent.
   Both agents would next perform connectivity checks and only then
   would they be ready to begin streaming media.

   These factors can lead to relatively lengthy session establishment
   times and thus to a degraded user experience.

   This document defines an alternative or supplementary mode of
   operation for ICE implementations, known as "Trickle ICE", in which
   candidates can be exchanged incrementally.  This enables ICE agents
   to exchange candidates as soon as an ICE negotiation session has been
   initiated.  Connectivity checks for a media stream can also start as
   soon as the first candidates for that stream become available.

   Trickle ICE can reduce session establishment times in cases where
   connectivity is confirmed for the first exchanged candidates (e.g.,
   where candidates for one of the agents are directly reachable from



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   the second agent, such as candidates at a media relay).  Even when
   this is not the case, performing candidate gathering for both agents
   and connectivity checks in parallel can considerably shorten ICE
   processing times.

   It is worth noting that there is quite a bit of operational
   experience with the Trickle ICE technique, going back as far as 2005
   (when the XMPP Jingle extension defined a "dribble mode" as specified
   in [XEP-0176]); this document incorporates feedback from those who
   have implemented and deployed the technique.

   In addition to the basics of Trickle ICE, this document also
   describes how to discover support for Trickle ICE, how regular ICE
   processing needs to be modified when building and updating check
   lists, and how Trickle ICE implementations interoperate with agents
   that only implement regular ICE processing as defined in
   [rfc5245bis].

   This specification does not define the usage of Trickle ICE with any
   specific signaling protocol (however, see
   [I-D.ietf-mmusic-trickle-ice-sip] for usage with SIP [RFC3261] and
   [XEP-0176] for usage with XMPP [RFC6120]).  Similarly, it does not
   define Trickle ICE in terms of the Session Description Protocol (SDP)
   [RFC4566] or the offer/answer model [RFC3264] because the technique
   can be and already is used in application protocols that are not tied
   to SDP or to offer/answer semantics.  However, because SDP and the
   offer/answer model are familiar to most readers of this
   specification, some examples in this document use those particulars
   in order to explain the underlying concepts.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   This specification makes use of all terminology defined for
   Interactive Connectivity Establishment in [rfc5245bis].  In addition,
   it defines the following terms:

   Candidate Gatherer:  A module used by an ICE agent to obtain local
      candidates.  Candidate gatherers use different mechanisms for
      discovering local candidates, such as STUN and TURN.

   Generation:  The complete set of candidates sent within an ICE
      negotiation session.





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   ICE Description:  Any session-related (as opposed to candidate-
      related) attributes required to configure an ICE agent.  These
      include but are not limited to "ice-ufrag", "ice-pwd", and "ice-
      options".

   ICE Negotiation Session:  A virtual session involving all of the
      interactions between ICE agents up until an ICE restart (if any).

   Initiator:  The ICE agent that starts an ICE negotiation session.

   Responder:  The ICE agent with which an initiator starts an ICE
      negotiation session.

   Trickled Candidates:  Candidates that a Trickle ICE agent sends after
      sending an initial ICE description or responding to an initial ICE
      description, but within the same ICE negotiation session.
      Trickled candidates can be sent in parallel with candidate
      gathering and connectivity checks.

   Trickling:  The act of sending trickled candidates.

   Half Trickle:  A Trickle ICE mode of operation where the initiator
      gathers its first generation of candidates strictly before
      creating and sending the initial ICE description.  Once sent, that
      ICE description can be processed by regular ICE agents and does
      not require support for this specification.  It also allows
      Trickle ICE capable responders to still gather candidates and
      perform connectivity checks in a non-blocking way, thus roughly
      providing "half" the advantages of Trickle ICE.  The mechanism is
      mostly meant for use in cases where the remote agent's support for
      Trickle ICE cannot be confirmed prior to sending an initial ICE
      description.

   Full Trickle:  The typical mode of operation for Trickle ICE agents,
      in which an initial ICE description can include any number of
      candidates (even zero candidates) and does not need to include the
      entire first generation of candidates as in half trickle.

3.  Determining Support for Trickle ICE

   To fully support Trickle ICE, applications SHOULD incorporate one of
   the following mechanisms to enable implementations to determine
   whether Trickle ICE is supported:

   1.  Provide a capabilities discovery method so that agents can verify
       support of Trickle ICE prior to initiating a session (XMPP's
       Service Discovery [XEP-0030] is one such mechanism).




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   2.  Make support for Trickle ICE mandatory so that user agents can
       assume support.

   If an application protocol does not provide a method of determining
   ahead of time whether Trickle ICE is supported, agents can make use
   of the half trickle procedure described in Section 14.

   Prior to sending an initial ICE description, agents using signaling
   protocols that support capabilities discovery can attempt to verify
   whether or not the remote party supports Trickle ICE.  If an agent
   determines that the remote party does not support Trickle ICE, it
   MUST fall back to using regular ICE or abandon the entire session.

   Even if a signaling protocol does not include a capabilities
   discovery method, a user agent can provide an indication within the
   ICE description that it supports Trickle ICE (e.g., in SDP this would
   be a token of "trickle" in the ice-options attribute).

   Dedicated discovery semantics and half trickle are needed only prior
   to session initiation.  After a session is established and Trickle
   ICE support is confirmed for both parties, either agent can use full
   trickle for subsequent exchanges.

4.  Sending the Initial ICE Description

   An agent can start gathering candidates as soon as it has an
   indication that communication is imminent (e.g., a user interface cue
   or an explicit request to initiate a session).  Unlike in regular
   ICE, in Trickle ICE implementations do not need to gather candidates
   in a blocking manner.  Therefore, unless half trickle is being used,
   agents SHOULD generate and transmit their initial ICE description as
   early as possible, so that the remote party can start gathering and
   trickling candidates.

   Trickle ICE agents MAY include any mix of candidates in an ICE
   description.  This includes the possibility of sending an ICE
   description that contains all the candidates that the agent plans to
   use (as in half trickle mode), sending an ICE description that
   contains only a publicly-reachable IP address (e.g., a candidate at a
   media relay that is known to not be behind a firewall), or sending an
   ICE description with no candidates at all (in which case the
   initiator can obtain the responder's initial candidate list sooner
   and the responder can begin candidate gathering more quickly).

   Methods for calculating priorities and foundations, as well as
   determining redundancy of candidates, work just as with regular ICE
   (with the exception of pruning of duplicate peer reflexive candidates
   as described under Section 5.2).



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5.  Receiving the Initial ICE Description

   When a responder receives an initial ICE description, it will first
   check if the ICE description or initiator indicates support for
   Trickle ICE as explained in Section 3.  If this is not the case, the
   agent MUST process the ICE description according to regular ICE
   procedures [rfc5245bis] (or, if no ICE support is detected at all,
   according to relevant processing rules for the underlying signaling
   protocol, such as offer/answer processing rules [RFC3264]).

   If support for Trickle ICE is confirmed, an agent will automatically
   assume support for regular ICE as well even if the support
   verification procedure in [rfc5245bis] indicates otherwise.
   Specifically, the rules from [rfc5245bis] would imply that ICE itself
   is not supported if the initial ICE description includes no
   candidates; however, such a conclusion is not warranted if the
   responder can confirm that the initiator supports Trickle ICE; in
   this case, fallback to [RFC3264] is not necessary.

   If the initial ICE description does indicate support for Trickle ICE,
   the agent will determine its role and start gathering and
   prioritizing candidates; while doing so, it will also respond by
   sending its own ICE description, so that both agents can start
   forming check lists and begin connectivity checks.

5.1.  Sending the Initial Response

   An agent can respond to an initial ICE description at any point while
   gathering candidates.  Here again the ICE description MAY contain any
   set of candidates, including all candidates or no candidates.  (The
   benefit of including no candidates is to send the ICE description as
   quickly as possible, so that both parties can consider the overall
   session to be under active negotiation as soon as possible.)

   As noted in Section 3, in application protocols that use SDP the
   responder's ICE description can indicate support for Trickle ICE by
   including a token of "trickle" in the ice-options attribute.

5.2.  Forming Check Lists and Beginning Connectivity Checks

   After the initiator and responder exchange ICE descriptions, and as
   soon as they have obtained local and remote candidates, agents begin
   forming candidate pairs, computing candidate pair priorities,
   ordering candidate pairs, pruning duplicate pairs, and creating check
   lists according to regular ICE procedures [rfc5245bis].

   According to those procedures, in order for candidate pairing to be
   possible and for duplicate candidates to be pruned, the candidates



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   would need to be provided in the relevant ICE descriptions.  Under
   Trickle ICE, check lists can be empty until candidate pairs are sent
   or received.  Therefore Trickle ICE agents handle check lists and
   candidate pairing in a slightly different way than regular ICE
   agents: the agents still create the check lists, but they populate
   the check lists only after they actually have the candidate pairs.

   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.

   With regard to pruning of duplicate candidate pairs, a Trickle ICE
   agent SHOULD follow a policy of "highest priority wins, except for
   peer reflexive candidates".

6.  Receiving the Initial Answer

   When processing an ICE description from a responder, the initiator
   follows regular ICE procedures to determine its role, after which it
   forms check lists (as described in Section 5.2) and begins
   connectivity checks.

7.  Performing Connectivity Checks

   For the most part, Trickle ICE agents perform connectivity checks
   following regular ICE procedures.  However, the fact that gathering
   and communicating candidates is asynchronous in Trickle ICE imposes a
   number of changes as described in the following sections.

7.1.  Scheduling Checks

   The ICE specification [rfc5245bis], Section 5.8, requires that agents
   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.

   Therefore, a Trickle ICE agent SHOULD NOT terminate the timer until
   the state of the check list is Completed or Failed as specified
   herein (see Section 8.2).




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7.2.  Check List and Timer State Updates

   The ICE specification [rfc5245bis], Section 7.1.3.3, requires that
   agents update check lists and timer states upon completing a
   connectivity check transaction.  During such an update, regular ICE
   agents would set the state of a check list to Failed if both of the
   following two conditions are satisfied:

   o  all of the pairs in the check list are either in the Failed state
      or Succeeded state; and

   o  there is not a pair in the valid list for each component of the
      media stream.

   With Trickle ICE, the above situation would often occur when
   candidate gathering and trickling are still in progress, even though
   it is quite possible that future checks will succeed.  For this
   reason, Trickle ICE agents add the following conditions to the above
   list:

   o  all candidate gatherers have completed and the agent is not
      expecting to discover any new local candidates;

   o  the remote agent has sent an end-of-candidates indication for that
      check list as described in Section 8.2.

   Regular ICE requires that agents then update all other check lists,
   placing one pair from each of them into the Waiting state,
   effectively unfreezing all remaining check lists.  However, under
   Trickle ICE other check lists might still be empty at that point.
   Therefore a Trickle ICE agent MUST monitor whether a check list is
   active or frozen independently of the state of the candidate pairs
   that the check list contains, and MUST consider a check list to be
   active when unfreezing the first candidate pair in the check list.
   When there is no candidate pair in a check list (i.e., when the check
   list is empty), a Trickle ICE agent MAY consider it to be either
   active or frozen.  An empty frozen check list SHOULD be changed to
   active if another check list is completely finished (i.e., every pair
   is either Successful or Failed), or if another checklist has a valid
   candidate pair for all components.

8.  Discovering and Sending Additional Local Candidates

   After ICE descriptions have been sent, agents will most likely
   continue discovering new local candidates as STUN, TURN, and other
   non-host candidate gathering mechanisms begin to yield results.
   Whenever an agent discovers such a new candidate it will compute its




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   priority, type, foundation and component ID according to regular ICE
   procedures.

   The new candidate is then checked for redundancy against the existing
   list of local candidates.  If its transport address and base match
   those of an existing candidate, it will be considered redundant and
   will be ignored.  This would often happen for server reflexive
   candidates that match the host addresses they were obtained from
   (e.g., when the latter are public IPv4 addresses).  Contrary to
   regular ICE, Trickle ICE agents will consider the new candidate
   redundant regardless of its priority.

   Next the agent sends (i.e., trickles) the newly discovered
   candidate(s) to the remote agent.  The actual delivery of the new
   candidates is handled by a signaling protocol such as SIP or XMPP.
   Trickle ICE imposes no restrictions on the way this is done (e.g.,
   some applications may choose not to send trickle updates for server
   reflexive candidates and instead rely on the discovery of peer
   reflexive ones).

   When trickle updates are sent, each candidate MUST be delivered to
   the receiving Trickle ICE implementation not more than once.  If
   there are any candidate retransmissions, they need to be hidden from
   the ICE implementation.

   Also, candidate trickling needs to be correlated to a specific ICE
   negotiation session, so that if there is an ICE restart, any delayed
   updates for a previous session can be recognized as such and ignored
   by the receiving party.  For example, applications that choose to
   signal candidates via SDP may include a ufrag value in the
   corresponding a=candidate line such as:


     a=candidate:1 1 UDP 2130706431 2001:db8::1 5000 typ host ufrag 8hhY


   Or as another example, WebRTC implementations may include a ufrag in
   the JavaScript objects that represent candidates.

   Note: The signaling protocol needs to provide a mechanism for both
   parties to indicate and agree on the ICE negotiation session in force
   (as identified by the ufrag) so that they have a consistent view of
   which candidates are to be paired.  This is especially important in
   the case of ICE restarts (see Section 13).

   Once the candidate has been sent to the remote party, the agent
   checks if any remote candidates are currently known for this same




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   stream.  If not, the new candidate will simply be added to the list
   of local candidates.

   Otherwise, if the agent has already learned of one or more remote
   candidates for this stream and component, it will begin pairing the
   new local candidates with them and adding the pairs to the existing
   check lists according to their priority.

   Note: A Trickle ICE agent MUST NOT pair a local candidate until it
   has been trickled to the remote agent.

8.1.  Pairing Newly Learned Candidates and Updating Check Lists

   Forming candidate pairs works as described in the ICE specification
   [rfc5245bis].  However, actually adding the new pair to a check list
   happens according to the rules described below.

   If the check list where the pair is to be added already contains the
   maximum number of candidate pairs (100 by default as per
   [rfc5245bis]), the new pair is discarded.

   If the new pair's local candidate is server reflexive, the server
   reflexive candidate MUST be replaced by its base before adding the
   pair to the list.

   Once this is done, the agent examines the check list looking for
   another pair that would be redundant with the new one.  If such a
   pair exists and the type of its remote candidate is not peer
   reflexive, the pair with the higher priority is kept and the one with
   the lower priority is discarded.  If, on the other hand, the type of
   the remote candidate in the pre-existing pair is peer reflexive, the
   agent MUST replace it with the newly formed pair (regardless of their
   respective priorities); this is done by setting the priority of the
   new candidate to the priority of the pre-existing candidate and then
   re-sorting the check list.

      Note: So that both agents will have the same view of candidate
      priorities, it is important to replacing existing pairs with
      seemingly equivalent higher-priority ones and to always update
      peer-reflexive candidates if equivalent alternatives are received
      through signaling.

   For all other pairs, including those with a server reflexive local
   candidate that were not found to be redundant, the rules specified in
   the following section apply.






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8.1.1.  Inserting a New Pair in a Check List

   Consider the following tabular representation of all checklists in an
   agent:


   +------------+------+------+------+------+------+
   |            |  f1  |  f2  |  f3  |  f4  |  f5  |
   +------------+------+------+------+------+------+
   | Audio.RTP  |  cp  |  cp  |  cp  |      |      |
   +------------+------+------+------+------+------+
   | Audio.RTCP |  cp  |  cp  |  cp  |  cp  |      |
   +------------+------+------+------+------+------+
   | Video.RTP  |  cp  |      |      |      |  cp  |
   +------------+------+------+------+------+------+
   | Video.RTCP |  cp  |      |      |      |  cp  |
   +------------+------+------+------+------+------+


                      Figure 1: Trickle State Updates

   Each row in the table represents a component for a given media
   stream.  Each column represents one foundation.  Each cell represents
   one candidate pair.

   When an agent commences ICE processing as per [rfc5245bis], it will
   unfreeze (i.e., place in the Waiting state) the topmost candidate
   pair in every column.  Then, as the checks proceed, for each pair
   that enters the Succeeded state the agent will unfreeze the pair that
   is immediately underneath the pair that succeeded (e.g., if the pair
   in column 1, row 1 succeeds then the agent will unfreeze the pair in
   column 1, row 2).  ICE also specifies that, if all the pairs in a
   media stream for one foundation are unfrozen (e.g., column 1, rows 1
   and 2 representing both components for the audio stream), then all of
   the candidate pairs in the entire column are unfrozen (e.g., column
   1, rows 3 and 4).

   Trickle ICE preserves all of these rules.  This implies that if, for
   some reason, a Trickle agent were to begin connectivity checks with
   all of its pairs already present, the way that pair states change is
   indistinguishable from that of a regular ICE agent.

   Of course, the major difference with Trickle ICE is that candidates
   can arrive after connectivity checks have started.  When this
   happens, an agent sets the state of the newly formed pair as follows:

   Waiting:   if the newly formed pair is the topmost pair in this
      column;



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   Waiting:   if the pair immediately above the newly formed pair in
      this column is in the Succeeded state;

   Waiting:   if there is at least one pair in this column below the row
      of the newly formed pair whose state is either Succeeded or
      Failed.

   Frozen:   in all other cases.

8.2.  Announcing End of Candidates

   Once all candidate gathering is completed or expires for a specific
   media stream, the agent will generate an "end-of-candidates"
   indication for that stream and send it to the remote agent via the
   signaling channel.  The exact form of the indication depends on the
   application protocol.  The indication can be sent in the following
   ways:

   o  As part of an initiation request (which would typically be the
      case with an initial ICE description for half trickle)

   o  Along with the last candidate an agent can send for a stream

   o  As a standalone notification (e.g., after STUN Binding requests or
      TURN Allocate requests to a server time out and the agent has no
      other active gatherers)

   Sending an end-of-candidates indication in a timely manner is
   important in order to avoid ambiguities and speed up the conclusion
   of ICE processing.  In particular:

   o  A controlled Trickle ICE agent SHOULD send an end-of-candidates
      indication after it has completed gathering for a media stream,
      unless ICE processing terminates before the agent has had a chance
      to complete gathering.

   o  A controlling agent MAY conclude ICE processing prior to sending
      end-of-candidates indications for all streams.  However, it is
      RECOMMENDED for a controlling agent to send end-of-candidates
      indications whenever possible for the sake of consistency and to
      keep middleboxes and controlled agents up-to-date on the state of
      ICE processing.

   When sending an end-of-candidates indication during trickling (rather
   than as a part of an initial ICE description or response), it is the
   responsibility of the using protocol to define methods for relating
   the indication to one or more specific media streams.




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   Receiving an end-of-candidates indication enables an agent to update
   check list states and, in case valid pairs do not exist for every
   component in every media stream, determine that ICE processing has
   failed.  It also enables agents to speed up the conclusion of ICE
   processing when a candidate pair has been validated but it involves
   the use of lower-preference transports such as TURN.  In such
   situations, an implementation MAY choose to wait and see if higher-
   priority candidates are received; in this case the end-of-candidates
   indication provides a notification that such candidates are not
   forthcoming.

   An agent MAY also choose to generate an end-of-candidates indication
   before candidate gathering has actually completed, if the agent
   determines that gathering has continued for more than an acceptable
   period of time.  However, an agent MUST NOT send any more candidates
   after it has sent an end-of-candidates indication.

   When performing half trickle, an agent SHOULD send an end-of-
   candidates indication together with its initial ICE description
   unless it is planning to potentially send additional candidates
   (e.g., in case the remote party turns out to support Trickle ICE).

   After an agent sends the end-of-candidates indication, it will update
   the state of the corresponding check list as explained in
   Section 7.2.  Past that point, an agent MUST NOT send any new
   candidates within this ICE negotiation session.  After an agent has
   received an end-of-candidates indication, it MUST also ignore any
   newly received candidates for that media stream or media session.
   Therefore, adding new candidates to the negotiation is possible only
   through an ICE restart (see Section 13).

   This specification does not override regular ICE semantics for
   concluding ICE processing.  Therefore, even if end-of-candidates
   indications are sent, agents will still have to go through pair
   nomination.  Also, if pairs have been nominated for components and
   media streams, ICE processing MAY still conclude even if end-of-
   candidates indications have not been received for all streams.

9.  Receiving Additional Remote Candidates

   At any time during ICE processing, a Trickle ICE agent might receive
   new candidates from the remote agent.  When this happens and no local
   candidates are currently known for this same stream, the new remote
   candidates are added to the list of remote candidates.

   Otherwise, the new candidates are used for forming candidate pairs
   with the pool of local candidates and they are added to the local
   check lists as described in Section 8.1.



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   Once the remote agent has completed candidate gathering, it will send
   an end-of-candidates indication.  Upon receiving such an indication,
   the local agent MUST update check list states as per Section 7.2.
   This might lead to some check lists being marked as Failed.

10.  Receiving an End-Of-Candidates Notification

   When an agent receives an end-of-candidates indication for a specific
   media stream, it will update the state of the relevant check list as
   per Section 7.2.  If the check list is still in the Active state
   after the update, the agent will persist the fact that an end-of-
   candidates indication has been received and take it into account in
   future updates to the check list.

11.  Trickle ICE and Peer Reflexive Candidates

   Even though Trickle ICE does not explicitly modify the procedures for
   handling peer-reflexive candidates, use of Trickle ICE can have an
   impact on how they are processed.  With Trickle ICE, it is possible
   that server reflexive candidates can be discovered as peer reflexive
   in cases where incoming connectivity checks are received from these
   candidates before the trickle updates that carry them.

   While this would certainly increase the number of cases where ICE
   processing nominates and selects candidates discovered as peer-
   reflexive, it does not require any change in processing.

   It is also likely that some applications would prefer not to trickle
   server reflexive candidates to entities that are known to be publicly
   accessible and where sending a direct STUN binding request is likely
   to reach the destination faster than the trickle update that travels
   through the signaling path.

12.  Concluding ICE Processing

   This specification does not directly modify the procedures for ending
   ICE processing described in Section 8 of [rfc5245bis], and Trickle
   ICE implementations follow the same rules.

13.  Subsequent Exchanges

   Either agent MAY generate a subsequent ICE description at any time
   allowed by [RFC3264].  When this happens agents will use [rfc5245bis]
   semantics to determine whether or not the new ICE description
   requires an ICE restart.  If an ICE restart occurs, the user agents
   can assume that Trickle ICE is still supported if support was
   determined previously, and thus can engage in Trickle ICE behavior as




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   they would in an initial exchange of ICE descriptions where support
   was determined through a capabilities discovery method.

14.  Unilateral Use of Trickle ICE (Half Trickle)

   In half trickle mode, the initiator sends a regular ICE description
   with a complete generation of candidates.  This ensures that the ICE
   description can be processed by a regular ICE responder and is mostly
   meant for use in cases where support for Trickle ICE cannot be
   confirmed prior to sending an initial ICE description.  The initial
   ICE description indicates support for Trickle ICE, which means the
   responder can respond with an incomplete generation of candidates and
   continue trickling the rest.  A half trickle ICE description would
   typically contain an end-of-candidates indication, although this is
   not mandatory because if trickle support is confirmed then the
   initiator can choose to trickle additional candidates before it sends
   an end-of-candidates indication.

   The half trickle mechanism can be used in cases where there is no way
   for an agent to verify in advance whether a remote party supports
   Trickle ICE.  Because the initial ICE description contains a full
   generation of candidates, it can thus be handled by a regular ICE
   agent, while still allowing a Trickle ICE agent to use the
   optimization defined in this specification.  This prevents
   negotiation from failing in the former case while still giving
   roughly half the Trickle ICE benefits in the latter (hence the name
   of the mechanism).

   Use of half trickle is only necessary during an initial exchange of
   ICE descriptions.  After both parties have received a session
   description from their peer, they can each reliably determine Trickle
   ICE support and use it for all subsequent exchanges.

   In some instances, using half trickle might bring more than just half
   the improvement in terms of user experience.  This can happen when an
   agent starts gathering candidates upon user interface cues that the
   user will soon be initiating an interaction, such as activity on a
   keypad or the phone going off hook.  This would mean that some or all
   of the candidate gathering could be completed before the agent
   actually needs to send the ICE description.  Because the responder
   will be able to trickle candidates, both agents will be able to start
   connectivity checks and complete ICE processing earlier than with
   regular ICE and potentially even as early as with full trickle.

   However, such anticipation is not always possible.  For example, a
   multipurpose user agent or a WebRTC web page where communication is a
   non-central feature (e.g., calling a support line in case of a
   problem with the main features) would not necessarily have a way of



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   distinguishing between call intentions and other user activity.  In
   such cases, using full trickle is most likely to result in an ideal
   user experience.  Even so, using half trickle would be an improvement
   over regular ICE because it would result in a better experience for
   responders.

15.  Requirements for Signaling Protocols

   In order to fully enable the use of Trickle ICE, this specification
   defines the following requirements for signaling protocols.

   o  A signaling protocol SHOULD provide a way for parties to advertise
      and discover support for Trickle ICE before an ICE negotiation
      session begins (see Section 3).

   o  A signaling protocol MUST provide methods for incrementally
      sending (i.e., "trickling") additional candidates after sending
      the initial ICE description (see Section 8).

   o  A signaling protocol MUST provide a mechanism for both parties to
      indicate and agree on the ICE negotiation session in force (see
      Section 8).

   o  A signaling protocol MUST provide a way for parties to communicate
      the end-of-candidates indication (see Section 8.2).

16.  Example Flow

   As an example, a typical successful Trickle ICE exchange with a
   signaling protocol that follows the offer/answer model would look
   this way:




















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           Alice                                            Bob
             |                     Offer                     |
             |---------------------------------------------->|
             |            Additional Candidates              |
             |---------------------------------------------->|
             |                                               |
             |                     Answer                    |
             |<----------------------------------------------|
             |            Additional Candidates              |
             |<----------------------------------------------|
             |                                               |
             | Additional Candidates and Connectivity Checks |
             |<--------------------------------------------->|
             |                                               |
             |<=============== MEDIA FLOWS =================>|



                             Figure 2: Example

17.  IANA Considerations

   This specification requests no actions from IANA.

18.  Security Considerations

   This specification inherits most of its semantics from [rfc5245bis]
   and as a result all security considerations described there apply to
   Trickle ICE.

   If the privacy implications of revealing host addresses on an
   endpoint device are a concern, agents can generate an ICE description
   that contains no candidates and then only trickle candidates that do
   not reveal host addresses (e.g., relayed candidates).

19.  Acknowledgements

   The authors would like to thank Bernard Aboba, Flemming Andreasen,
   Rajmohan Banavi, Taylor Brandstetter, Christer Holmberg, Jonathan
   Lennox, Enrico Marocco, Pal Martinsen, Martin Thomson, Dale R.
   Worley, and Brandon Williams for their reviews and suggestions on
   improving this document.

20.  References







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20.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [rfc5245bis]
              Keranen, A., Keranen, A., and J. Rosenberg, "Interactive
              Connectivity Establishment (ICE): A Protocol for Network
              Address Translator (NAT) Traversal", draft-ietf-ice-
              rfc5245bis-08 (work in progress), December 2016.

20.2.  Informative References

   [I-D.ietf-mmusic-trickle-ice-sip]
              Ivov, E., Thomas, T., Marocco, E., and C. Holmberg, "A
              Session Initiation Protocol (SIP) usage for Trickle ICE",
              draft-ietf-mmusic-trickle-ice-sip-06 (work in progress),
              October 2016.

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
              <http://www.rfc-editor.org/info/rfc1918>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264, June
              2002.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC4787]  Audet, F., Ed. and C. Jennings, "Network Address
              Translation (NAT) Behavioral Requirements for Unicast
              UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
              2007, <http://www.rfc-editor.org/info/rfc4787>.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              DOI 10.17487/RFC5389, October 2008,
              <http://www.rfc-editor.org/info/rfc5389>.






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   [RFC5766]  Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
              Relays around NAT (TURN): Relay Extensions to Session
              Traversal Utilities for NAT (STUN)", RFC 5766, April 2010.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, March 2011.

   [XEP-0030]
              Hildebrand, J., Millard, P., Eatmon, R., and P. Saint-
              Andre, "XEP-0030: Service Discovery", XEP XEP-0030, June
              2008.

   [XEP-0176]
              Beda, J., Ludwig, S., Saint-Andre, P., Hildebrand, J.,
              Egan, S., and R. McQueen, "XEP-0176: Jingle ICE-UDP
              Transport Method", XEP XEP-0176, June 2009.

Appendix A.  Interaction with Regular ICE

   The ICE protocol was designed to be flexible enough to work in and
   adapt to as many network environments as possible.  Despite that
   flexibility, ICE as specified in [rfc5245bis] does not by itself
   support trickle ICE.  This section describes how trickling of
   candidates interacts with ICE.

   [rfc5245bis] describes the conditions required to update check lists
   and timer states while an ICE agent is in the Running state.  These
   conditions are verified upon transaction completion and one of them
   stipulates that:

      If there is not a pair in the valid list for each component of the
      media stream, the state of the check list is set to Failed.

   This could be a problem and cause ICE processing to fail prematurely
   in a number of scenarios.  Consider the following case:

   1.  Alice and Bob are both located in different networks with Network
       Address Translation (NAT).  Alice and Bob themselves have
       different address but both networks use the same [RFC1918] block.

   2.  Alice sends Bob the candidate 2001:db8:a0b:12f0::10 which also
       happens to correspond to an existing host on Bob's network.

   3.  Bob creates a check list consisting solely of
       2001:db8:a0b:12f0::10 and starts checks.






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   4.  These checks reach the host at 2001:db8:a0b:12f0::10 in Bob's
       network, which responds with an ICMP "port unreachable" error and
       per [rfc5245bis] Bob marks the transaction as Failed.

   At this point the check list only contains Failed candidates and the
   valid list is empty.  This causes the media stream and potentially
   all ICE processing to fail.

   A similar race condition would occur if the initial ICE description
   from Alice only contains candidates that can be determined as
   unreachable from any of the candidates that Bob has gathered (e.g.,
   this would be the case if Bob's candidates only contain IPv4
   addresses and the first candidate that he receives from Alice is an
   IPv6 one).

   Another potential problem could arise when a non-trickle ICE
   implementation initiates an interaction with a Trickle ICE
   implementation.  Consider the following case:

   1.  Alice's client has a non-Trickle ICE implementation.

   2.  Bob's client has support for Trickle ICE.

   3.  Alice and Bob are behind NATs with address-dependent filtering
       [RFC4787].

   4.  Bob has two STUN servers but one of them is currently
       unreachable.

   After Bob's agent receives Alice's initial ICE description it would
   immediately start connectivity checks.  It would also start gathering
   candidates, which would take a long time because of the unreachable
   STUN server.  By the time Bob's answer is ready and sent to Alice,
   Bob's connectivity checks may well have failed: until Alice gets
   Bob's answer, she won't be able to start connectivity checks and
   punch holes in her NAT.  The NAT would hence be filtering Bob's
   checks as originating from an unknown endpoint.

Appendix B.  Interaction with ICE Lite

   The behavior of ICE lite agents that are capable of Trickle ICE does
   not require any particular rules other than those already defined in
   this specification and [rfc5245bis].  This section is hence provided
   only for informational purposes.

   An ICE lite agent would generate an ICE description as per
   [rfc5245bis] and would indicate support for Trickle ICE.  Given that
   they will contain a complete generation of candidates, these ICE



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   descriptions would also be accompanied by an end-of-candidates
   indication.

   When performing full trickle, a full ICE implementation could send an
   initial ICE description or response with no candidates.  After
   receiving a response that identifies the remote agent as an ICE lite
   implementation, the initiator can choose to not send any additional
   candidates.  The same is also true in the case when the ICE lite
   agent initiates the interaction and the full ICE agent is the
   responder.  In these cases the connectivity checks would be enough
   for the ICE lite implementation to discover all potentially useful
   candidates as peer reflexive.  The following example illustrates one
   such ICE session using SDP syntax:


           ICE Lite                                          Bob
            Agent
              |   Offer (a=ice-lite a=ice-options:trickle)    |
              |---------------------------------------------->|
              |                                               |no cand
              |         Answer (a=ice-options:trickle)        |trickling
              |<----------------------------------------------|
              |              Connectivity Checks              |
              |<--------------------------------------------->|
     peer rflx|                                               |
    cand disco|                                               |
              |                                               |
              |<=============== MEDIA FLOWS =================>|



                             Figure 3: Example

   In addition to reducing signaling traffic this approach also removes
   the need to discover STUN bindings or make TURN allocations, which
   may considerably lighten ICE processing.

Appendix C.  Preserving Candidate Order while Trickling

   One important aspect of regular ICE is that connectivity checks for a
   specific foundation and component are attempted simultaneously by
   both agents, so that any firewalls or NATs fronting the agents would
   whitelist both endpoints and allow all except for the first
   ("suicide") packets to go through.  This is also important to
   unfreezing candidates at the right time.  While not crucial,
   preserving this behavior in Trickle ICE is likely to improve ICE
   performance.




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   To achieve this, when trickling candidates agents MUST respect the
   order in which the components and streams as they have been
   negotiated appear (implicitly or explicitly) in the relevant ICE
   descriptions.  Therefore a candidate for a specific component MUST
   NOT be sent prior to candidates for other components within the same
   foundation.

   For example, the following SDP description contains two components
   (RTP and RTCP) and two foundations (host and server reflexive):


     v=0
     o=jdoe 2890844526 2890842807 IN IP6 2001:db8:a0b:12f0::1
     s=
     c=IN IP4 2001:db8:a0b:12f0::1
     t=0 0
     a=ice-pwd:asd88fgpdd777uzjYhagZg
     a=ice-ufrag:8hhY
     m=audio 5000 RTP/AVP 0
     a=rtpmap:0 PCMU/8000
     a=candidate:1 1 UDP 2130706431 2001:db8:a0b:12f0::1 5000 typ host
     a=candidate:1 2 UDP 2130706431 2001:db8:a0b:12f0::1 5001 typ host
     a=candidate:2 1 UDP 1694498815 2001:db8:a0b:12f0::3 5000 typ srflx
         raddr 2001:db8:a0b:12f0::1 rport 8998
     a=candidate:2 2 UDP 1694498815 2001:db8:a0b:12f0::3 5001 typ srflx
         raddr 2001:db8:a0b:12f0::1 rport 8998


   For this description the RTCP host candidate MUST NOT be sent prior
   to the RTP host candidate.  Similarly the RTP server reflexive
   candidate MUST be sent together with or prior to the RTCP server
   reflexive candidate.

   Similar considerations apply at the level of media streams in
   addition to foundations; this is covered by the requirement to always
   start unfreezing candidates starting from the first media stream as
   described under Section 5.2.

Appendix D.  Changes from Earlier Versions

   Note to the RFC-Editor: please remove this section prior to
   publication as an RFC.

D.1.  Changes from draft-ietf-ice-trickle-04

   o  Removed dependency on SDP and offer/answer model.





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   o  Removed mentions of aggressive nomination, since it is deprecated
      in 5245bis.

   o  Added section on requirements for signaling protocols.

   o  Clarified terminology.

   o  Addressed various WG feedback.

D.2.  Changes from draft-ietf-ice-trickle-03

   o  Copy edit.

D.3.  Changes from draft-ietf-ice-trickle-03

   o  Provided more detailed description of unfreezing behavior,
      specifically how to replace pre-existing peer-reflexive candidates
      with higher-priority ones received via trickling.

D.4.  Changes from draft-ietf-ice-trickle-02

   o  Adjusted unfreezing behavior when there are disparate foundations.

D.5.  Changes from draft-ietf-ice-trickle-01

   o  Changed examples to use IPv6.

D.6.  Changes from draft-ietf-ice-trickle-00

   o  Removed dependency on SDP (which is to be provided in a separate
      specification).

   o  Clarified text about the fact that a check list can be empty if no
      candidates have been sent or received yet.

   o  Clarified wording about check list states so as not to define new
      states for "Active" and "Frozen" because those states are not
      defined for check lists (only for candidate pairs) in ICE core.

   o  Removed open issues list because it was out of date.

   o  Completed a thorough copy edit.

D.7.  Changes from draft-mmusic-trickle-ice-02

   o  Addressed feedback from Rajmohan Banavi and Brandon Williams.





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   o  Clarified text about determining support and about how to proceed
      if it can be determined that the answering agent does not support
      Trickle ICE.

   o  Clarified text about check list and timer updates.

   o  Clarified when it is appropriate to use half trickle or to send no
      candidates in an offer or answer.

   o  Updated the list of open issues.

D.8.  Changes from draft-ivov-01 and draft-mmusic-00

   o  Added a requirement to trickle candidates by order of components
      to avoid deadlocks in the unfreezing algorithm.

   o  Added an informative note on peer-reflexive candidates explaining
      that nothing changes for them semantically but they do become a
      more likely occurrence for Trickle ICE.

   o  Limit the number of pairs to 100 to comply with 5245.

   o  Added clarifications on the non-importance of how newly discovered
      candidates are trickled/sent to the remote party or if this is
      done at all.

   o  Added transport expectations for trickled candidates as per Dale
      Worley's recommendation.

D.9.  Changes from draft-ivov-00

   o  Specified that end-of-candidates is a media level attribute which
      can of course appear as session level, which is equivalent to
      having it appear in all m-lines.  Also made end-of-candidates
      optional for cases such as aggressive nomination for controlled
      agents.

   o  Added an example for ICE lite and Trickle ICE to illustrate how,
      when talking to an ICE lite agent doesn't need to send or even
      discover any candidates.

   o  Added an example for ICE lite and Trickle ICE to illustrate how,
      when talking to an ICE lite agent doesn't need to send or even
      discover any candidates.

   o  Added wording that explicitly states ICE lite agents have to be
      prepared to receive no candidates over signaling and that they




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      should not freak out if this happens.  (Closed the corresponding
      open issue).

   o  It is now mandatory to use MID when trickling candidates and using
      m-line indexes is no longer allowed.

   o  Replaced use of 0.0.0.0 to IP6 :: in order to avoid potential
      issues with RFC2543 SDP libraries that interpret 0.0.0.0 as an on-
      hold operation.  Also changed the port number here from 1 to 9
      since it already has a more appropriate meaning.  (Port change
      suggested by Jonathan Lennox).

   o  Closed the Open Issue about use about what to do with cands
      received after end-of-cands.  Solution: ignore, do an ICE restart
      if you want to add something.

   o  Added more terminology, including trickling, trickled candidates,
      half trickle, full trickle,

   o  Added a reference to the SIP usage for Trickle ICE as requested at
      the Boston interim.

D.10.  Changes from draft-rescorla-01

   o  Brought back explicit use of Offer/Answer.  There are no more
      attempts to try to do this in an O/A independent way.  Also
      removed the use of ICE Descriptions.

   o  Added SDP specification for trickled candidates, the trickle
      option and 0.0.0.0 addresses in m-lines, and end-of-candidates.

   o  Support and Discovery.  Changed that section to be less abstract.
      As discussed in IETF85, the draft now says implementations and
      usages need to either determine support in advance and directly
      use trickle, or do half trickle.  Removed suggestion about use of
      discovery in SIP or about letting implementing protocols do what
      they want.

   o  Defined Half Trickle.  Added a section that says how it works.
      Mentioned that it only needs to happen in the first o/a (not
      necessary in updates), and added Jonathan's comment about how it
      could, in some cases, offer more than half the improvement if you
      can pre-gather part or all of your candidates before the user
      actually presses the call button.

   o  Added a short section about subsequent offer/answer exchanges.





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   o  Added a short section about interactions with ICE Lite
      implementations.

   o  Added two new entries to the open issues section.

D.11.  Changes from draft-rescorla-00

   o  Relaxed requirements about verifying support following a
      discussion on MMUSIC.

   o  Introduced ICE descriptions in order to remove ambiguous use of
      3264 language and inappropriate references to offers and answers.

   o  Removed inappropriate assumption of adoption by RTCWEB pointed out
      by Martin Thomson.

Authors' Addresses

   Emil Ivov
   Atlassian
   303 Colorado Street, #1600
   Austin  78701
   USA

   Phone: +1-512-640-3000
   Email: eivov@atlassian.com


   Eric Rescorla
   RTFM, Inc.
   2064 Edgewood Drive
   Palo Alto, CA  94303
   USA

   Phone: +1 650 678 2350
   Email: ekr@rtfm.com


   Justin Uberti
   Google
   747 6th St S
   Kirkland, WA  98033
   USA

   Phone: +1 857 288 8888
   Email: justin@uberti.name





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   Peter Saint-Andre
   Filament
   P.O. Box 787
   Parker, CO  80134
   USA

   Phone: +1 720 256 6756
   Email: peter@filament.com
   URI:   https://filament.com/










































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