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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-18) exists of draft-ietf-mmusic-trickle-ice-sip-06 -- Obsolete informational reference (is this intentional?): RFC 4566 (Obsoleted by RFC 8866) -- Obsolete informational reference (is this intentional?): RFC 5389 (Obsoleted by RFC 8489) -- Obsolete informational reference (is this intentional?): RFC 5766 (Obsoleted by RFC 8656) Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group E. Ivov 3 Internet-Draft Atlassian 4 Intended status: Standards Track E. Rescorla 5 Expires: August 31, 2017 RTFM, Inc. 6 J. Uberti 7 Google 8 P. Saint-Andre 9 Filament 10 February 27, 2017 12 Trickle ICE: Incremental Provisioning of Candidates for the Interactive 13 Connectivity Establishment (ICE) Protocol 14 draft-ietf-ice-trickle-07 16 Abstract 18 This document describes "Trickle ICE", an extension to the 19 Interactive Connectivity Establishment (ICE) protocol that enables 20 ICE agents to send and receive candidates incrementally rather than 21 exchanging complete lists. With such incremental provisioning, ICE 22 agents can begin connectivity checks while they are still gathering 23 candidates and considerably shorten the time necessary for ICE 24 processing to complete. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on August 31, 2017. 43 Copyright Notice 45 Copyright (c) 2017 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 61 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 62 3. Determining Support for Trickle ICE . . . . . . . . . . . . . 5 63 4. Sending the Initial ICE Description . . . . . . . . . . . . . 6 64 5. Receiving the Initial ICE Description . . . . . . . . . . . . 7 65 5.1. Sending the Initial Response . . . . . . . . . . . . . . 7 66 5.2. Forming Check Lists and Beginning Connectivity 67 Checks . . . . . . . . . . . . . . . . . . . . . . . . . 7 68 6. Receiving the Initial Answer . . . . . . . . . . . . . . . . 8 69 7. Performing Connectivity Checks . . . . . . . . . . . . . . . 8 70 7.1. Scheduling Checks . . . . . . . . . . . . . . . . . . . . 8 71 7.2. Check List and Timer State Updates . . . . . . . . . . . 9 72 8. Discovering and Sending Additional Local Candidates . . . . . 9 73 8.1. Pairing Newly Learned Candidates and Updating 74 Check Lists . . . . . . . . . . . . . . . . . . . . . . . 11 75 8.1.1. Inserting a New Pair in a Check List . . . . . . . . 12 76 8.2. Announcing End of Candidates . . . . . . . . . . . . . . 13 77 9. Receiving Additional Remote Candidates . . . . . . . . . . . 14 78 10. Receiving an End-Of-Candidates Notification . . . . . . . . . 15 79 11. Trickle ICE and Peer Reflexive Candidates . . . . . . . . . . 15 80 12. Concluding ICE Processing . . . . . . . . . . . . . . . . . . 15 81 13. Subsequent Exchanges . . . . . . . . . . . . . . . . . . . . 15 82 14. Unilateral Use of Trickle ICE (Half Trickle) . . . . . . . . 16 83 15. Requirements for Signaling Protocols . . . . . . . . . . . . 17 84 16. Example Flow . . . . . . . . . . . . . . . . . . . . . . . . 17 85 17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 86 18. Security Considerations . . . . . . . . . . . . . . . . . . . 18 87 19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18 88 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 89 20.1. Normative References . . . . . . . . . . . . . . . . . . 19 90 20.2. Informative References . . . . . . . . . . . . . . . . . 19 91 Appendix A. Interaction with Regular ICE . . . . . . . . . . . . 20 92 Appendix B. Interaction with ICE Lite . . . . . . . . . . . . . 21 93 Appendix C. Preserving Candidate Order while Trickling . . . . . 22 94 Appendix D. Changes from Earlier Versions . . . . . . . . . . . 23 95 D.1. Changes from draft-ietf-ice-trickle-04 . . . . . . . . . 23 96 D.2. Changes from draft-ietf-ice-trickle-03 . . . . . . . . . 24 97 D.3. Changes from draft-ietf-ice-trickle-03 . . . . . . . . . 24 98 D.4. Changes from draft-ietf-ice-trickle-02 . . . . . . . . . 24 99 D.5. Changes from draft-ietf-ice-trickle-01 . . . . . . . . . 24 100 D.6. Changes from draft-ietf-ice-trickle-00 . . . . . . . . . 24 101 D.7. Changes from draft-mmusic-trickle-ice-02 . . . . . . . . 24 102 D.8. Changes from draft-ivov-01 and draft-mmusic-00 . . . . . 25 103 D.9. Changes from draft-ivov-00 . . . . . . . . . . . . . . . 25 104 D.10. Changes from draft-rescorla-01 . . . . . . . . . . . . . 26 105 D.11. Changes from draft-rescorla-00 . . . . . . . . . . . . . 27 106 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 108 1. Introduction 110 The Interactive Connectivity Establishment (ICE) protocol 111 [rfc5245bis] describes mechanisms for gathering candidates, 112 prioritizing them, choosing default ones, exchanging them with a 113 remote party, pairing them, and ordering them into check lists. Once 114 all of these actions have been completed (and only then), the parties 115 can begin a phase of connectivity checks and eventually select the 116 pair of candidates that will be used in a media session or for a 117 given media stream. 119 Although the sequence described above has the advantage of being 120 relatively straightforward to implement and debug once deployed, it 121 can also be rather lengthy. Candidate gathering often involves 122 things like querying STUN [RFC5389] servers and allocating relayed 123 candidates at TURN [RFC5766] servers. All of these actions can be 124 delayed for a noticeable amount of time; although they can be run in 125 parallel, they still need to respect the pacing requirements from 126 [rfc5245bis], which is likely to delay them even further. Some or 127 all of these actions also need be completed by the remote agent. 128 Both agents would next perform connectivity checks and only then 129 would they be ready to begin streaming media. 131 These factors can lead to relatively lengthy session establishment 132 times and thus to a degraded user experience. 134 This document defines an alternative or supplementary mode of 135 operation for ICE implementations, known as "Trickle ICE", in which 136 candidates can be exchanged incrementally. This enables ICE agents 137 to exchange candidates as soon as an ICE negotiation session has been 138 initiated. Connectivity checks for a media stream can also start as 139 soon as the first candidates for that stream become available. 141 Trickle ICE can reduce session establishment times in cases where 142 connectivity is confirmed for the first exchanged candidates (e.g., 143 where candidates for one of the agents are directly reachable from 144 the second agent, such as candidates at a media relay). Even when 145 this is not the case, performing candidate gathering for both agents 146 and connectivity checks in parallel can considerably shorten ICE 147 processing times. 149 It is worth noting that there is quite a bit of operational 150 experience with the Trickle ICE technique, going back as far as 2005 151 (when the XMPP Jingle extension defined a "dribble mode" as specified 152 in [XEP-0176]); this document incorporates feedback from those who 153 have implemented and deployed the technique. 155 In addition to the basics of Trickle ICE, this document also 156 describes how to discover support for Trickle ICE, how regular ICE 157 processing needs to be modified when building and updating check 158 lists, and how Trickle ICE implementations interoperate with agents 159 that only implement regular ICE processing as defined in 160 [rfc5245bis]. 162 This specification does not define the usage of Trickle ICE with any 163 specific signaling protocol (however, see 164 [I-D.ietf-mmusic-trickle-ice-sip] for usage with SIP [RFC3261] and 165 [XEP-0176] for usage with XMPP [RFC6120]). Similarly, it does not 166 define Trickle ICE in terms of the Session Description Protocol (SDP) 167 [RFC4566] or the offer/answer model [RFC3264] because the technique 168 can be and already is used in application protocols that are not tied 169 to SDP or to offer/answer semantics. However, because SDP and the 170 offer/answer model are familiar to most readers of this 171 specification, some examples in this document use those particulars 172 in order to explain the underlying concepts. 174 2. Terminology 176 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 177 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 178 document are to be interpreted as described in [RFC2119]. 180 This specification makes use of all terminology defined for 181 Interactive Connectivity Establishment in [rfc5245bis]. In addition, 182 it defines the following terms: 184 Candidate Gatherer: A module used by an ICE agent to obtain local 185 candidates. Candidate gatherers use different mechanisms for 186 discovering local candidates, such as STUN and TURN. 188 Generation: All of the candidates sent within an ICE negotiation 189 session; these are the candidates that are associated with a local 190 /remote ufrag pair (which will change on ICE restart, if any). 192 ICE Description: Any session-related (as opposed to candidate- 193 related) attributes required to configure an ICE agent. These 194 include but are not limited to "ice-ufrag", "ice-pwd", and "ice- 195 options". 197 ICE Negotiation Session: A virtual session involving all of the 198 interactions between ICE agents up until an ICE restart (if any). 200 Initiator: The ICE agent that starts an ICE negotiation session. 202 Responder: The ICE agent with which an initiator starts an ICE 203 negotiation session. 205 Trickled Candidates: Candidates that a Trickle ICE agent sends after 206 sending an initial ICE description or responding to an initial ICE 207 description, but within the same ICE negotiation session. 208 Trickled candidates can be sent in parallel with candidate 209 gathering and connectivity checks. 211 Trickling: The act of sending trickled candidates. 213 Half Trickle: A Trickle ICE mode of operation where the initiator 214 gathers a full generation of candidates strictly before creating 215 and sending the initial ICE description. Once sent, that ICE 216 description can be processed by regular ICE agents and does not 217 require support for this specification. It also allows Trickle 218 ICE capable responders to still gather candidates and perform 219 connectivity checks in a non-blocking way, thus roughly providing 220 "half" the advantages of Trickle ICE. The mechanism is mostly 221 meant for use in cases where the remote agent's support for 222 Trickle ICE cannot be confirmed prior to sending an initial ICE 223 description. 225 Full Trickle: The typical mode of operation for Trickle ICE agents, 226 in which an initial ICE description can include any number of 227 candidates (even zero candidates) and does not need to include a 228 full generation of candidates as in half trickle. 230 3. Determining Support for Trickle ICE 232 To fully support Trickle ICE, applications SHOULD incorporate one of 233 the following mechanisms to enable implementations to determine 234 whether Trickle ICE is supported: 236 1. Provide a capabilities discovery method so that agents can verify 237 support of Trickle ICE prior to initiating a session (XMPP's 238 Service Discovery [XEP-0030] is one such mechanism). 240 2. Make support for Trickle ICE mandatory so that user agents can 241 assume support. 243 If an application protocol does not provide a method of determining 244 ahead of time whether Trickle ICE is supported, agents can make use 245 of the half trickle procedure described in Section 14. 247 Prior to sending an initial ICE description, agents using signaling 248 protocols that support capabilities discovery can attempt to verify 249 whether or not the remote party supports Trickle ICE. If an agent 250 determines that the remote party does not support Trickle ICE, it 251 MUST fall back to using regular ICE or abandon the entire session. 253 Even if a signaling protocol does not include a capabilities 254 discovery method, a user agent can provide an indication within the 255 ICE description that it supports Trickle ICE (e.g., in SDP this would 256 be a token of "trickle" in the ice-options attribute). 258 Dedicated discovery semantics and half trickle are needed only prior 259 to session initiation. After a session is established and Trickle 260 ICE support is confirmed for both parties, either agent can use full 261 trickle for subsequent exchanges. 263 4. Sending the Initial ICE Description 265 An agent can start gathering candidates as soon as it has an 266 indication that communication is imminent (e.g., a user interface cue 267 or an explicit request to initiate a session). Unlike in regular 268 ICE, in Trickle ICE implementations do not need to gather candidates 269 in a blocking manner. Therefore, unless half trickle is being used, 270 agents SHOULD generate and transmit their initial ICE description as 271 early as possible, so that the remote party can start gathering and 272 trickling candidates. 274 Trickle ICE agents MAY include any mix of candidates in an ICE 275 description. This includes the possibility of sending an ICE 276 description that contains all the candidates that the agent plans to 277 use (as in half trickle mode), sending an ICE description that 278 contains only a publicly-reachable IP address (e.g., a candidate at a 279 media relay that is known to not be behind a firewall), or sending an 280 ICE description with no candidates at all (in which case the 281 initiator can obtain the responder's initial candidate list sooner 282 and the responder can begin candidate gathering more quickly). 284 Methods for calculating priorities and foundations, as well as 285 determining redundancy of candidates, work just as with regular ICE 286 (with the exception of pruning of duplicate peer reflexive candidates 287 as described under Section 5.2). 289 5. Receiving the Initial ICE Description 291 When a responder receives an initial ICE description, it will first 292 check if the ICE description or initiator indicates support for 293 Trickle ICE as explained in Section 3. If this is not the case, the 294 agent MUST process the ICE description according to regular ICE 295 procedures [rfc5245bis] (or, if no ICE support is detected at all, 296 according to relevant processing rules for the underlying signaling 297 protocol, such as offer/answer processing rules [RFC3264]). 299 If support for Trickle ICE is confirmed, an agent will automatically 300 assume support for regular ICE as well even if the support 301 verification procedure in [rfc5245bis] indicates otherwise. 302 Specifically, the rules from [rfc5245bis] would imply that ICE itself 303 is not supported if the initial ICE description includes no 304 candidates; however, such a conclusion is not warranted if the 305 responder can confirm that the initiator supports Trickle ICE; in 306 this case, fallback to [RFC3264] is not necessary. 308 If the initial ICE description does indicate support for Trickle ICE, 309 the agent will determine its role and start gathering and 310 prioritizing candidates; while doing so, it will also respond by 311 sending its own ICE description, so that both agents can start 312 forming check lists and begin connectivity checks. 314 5.1. Sending the Initial Response 316 An agent can respond to an initial ICE description at any point while 317 gathering candidates. Here again the ICE description MAY contain any 318 set of candidates, including all candidates or no candidates. (The 319 benefit of including no candidates is to send the ICE description as 320 quickly as possible, so that both parties can consider the overall 321 session to be under active negotiation as soon as possible.) 323 As noted in Section 3, in application protocols that use SDP the 324 responder's ICE description can indicate support for Trickle ICE by 325 including a token of "trickle" in the ice-options attribute. 327 5.2. Forming Check Lists and Beginning Connectivity Checks 329 After the initiator and responder exchange ICE descriptions, and as 330 soon as they have obtained local and remote candidates, agents begin 331 forming candidate pairs, computing candidate pair priorities, 332 ordering candidate pairs, pruning duplicate pairs, and creating check 333 lists according to regular ICE procedures [rfc5245bis]. 335 According to those procedures, in order for candidate pairing to be 336 possible and for duplicate candidates to be pruned, the candidates 337 would need to be provided in the relevant ICE descriptions. Under 338 Trickle ICE, check lists can be empty until candidate pairs are sent 339 or received. Therefore Trickle ICE agents handle check lists and 340 candidate pairing in a slightly different way than regular ICE 341 agents: the agents still create the check lists, but they populate 342 the check lists only after they actually have the candidate pairs. 344 A Trickle ICE agent initially considers all check lists to be frozen. 345 It then inspects the first check list and attempts to unfreeze all 346 candidate pairs it has received so far that belong to the first 347 component on the first media stream (i.e., the first media stream 348 that was reported to the ICE implementation from the using 349 application). If that first component of the first media stream does 350 not contain candidates for one or more of the currently known pair 351 foundations, and if candidate pairs already exist for that foundation 352 in one of the following components or media streams, then the agent 353 unfreezes the first of those candidate pairs. 355 With regard to pruning of duplicate candidate pairs, a Trickle ICE 356 agent SHOULD follow a policy of "highest priority wins, except for 357 peer reflexive candidates". 359 6. Receiving the Initial Answer 361 When processing an ICE description from a responder, the initiator 362 follows regular ICE procedures to determine its role, after which it 363 forms check lists (as described in Section 5.2) and begins 364 connectivity checks. 366 7. Performing Connectivity Checks 368 For the most part, Trickle ICE agents perform connectivity checks 369 following regular ICE procedures. However, the fact that gathering 370 and communicating candidates is asynchronous in Trickle ICE imposes a 371 number of changes as described in the following sections. 373 7.1. Scheduling Checks 375 The ICE specification [rfc5245bis], Section 5.8, requires that agents 376 terminate the timer for a triggered check in relation to an active 377 check list once the agent has exhausted all frozen pairs in the check 378 list. This will not work with Trickle ICE, because more pairs will 379 be added to the check list incrementally. 381 Therefore, a Trickle ICE agent SHOULD NOT terminate the timer until 382 the state of the check list is Completed or Failed as specified 383 herein (see Section 8.2). 385 7.2. Check List and Timer State Updates 387 The ICE specification [rfc5245bis], Section 7.1.3.3, requires that 388 agents update check lists and timer states upon completing a 389 connectivity check transaction. During such an update, regular ICE 390 agents would set the state of a check list to Failed if both of the 391 following two conditions are satisfied: 393 o all of the pairs in the check list are either in the Failed state 394 or Succeeded state; and 396 o there is not a pair in the valid list for each component of the 397 media stream. 399 With Trickle ICE, the above situation would often occur when 400 candidate gathering and trickling are still in progress, even though 401 it is quite possible that future checks will succeed. For this 402 reason, Trickle ICE agents add the following conditions to the above 403 list: 405 o all candidate gatherers have completed and the agent is not 406 expecting to discover any new local candidates; 408 o the remote agent has sent an end-of-candidates indication for that 409 check list as described in Section 8.2. 411 Regular ICE requires that agents then update all other check lists, 412 placing one pair from each of them into the Waiting state, 413 effectively unfreezing all remaining check lists. However, under 414 Trickle ICE other check lists might still be empty at that point. 415 Therefore a Trickle ICE agent MUST monitor whether a check list is 416 active or frozen independently of the state of the candidate pairs 417 that the check list contains, and MUST consider a check list to be 418 active when unfreezing the first candidate pair in the check list. 419 When there is no candidate pair in a check list (i.e., when the check 420 list is empty), a Trickle ICE agent MAY consider it to be either 421 active or frozen. An empty frozen check list SHOULD be changed to 422 active if another check list is completely finished (i.e., every pair 423 is either Successful or Failed), or if another checklist has a valid 424 candidate pair for all components. 426 8. Discovering and Sending Additional Local Candidates 428 After ICE descriptions have been sent, agents will most likely 429 continue discovering new local candidates as STUN, TURN, and other 430 non-host candidate gathering mechanisms begin to yield results. 431 Whenever an agent discovers such a new candidate it will compute its 432 priority, type, foundation and component ID according to regular ICE 433 procedures. 435 The new candidate is then checked for redundancy against the existing 436 list of local candidates. If its transport address and base match 437 those of an existing candidate, it will be considered redundant and 438 will be ignored. This would often happen for server reflexive 439 candidates that match the host addresses they were obtained from 440 (e.g., when the latter are public IPv4 addresses). Contrary to 441 regular ICE, Trickle ICE agents will consider the new candidate 442 redundant regardless of its priority. 444 Next the agent sends (i.e., trickles) the newly discovered 445 candidate(s) to the remote agent. The actual delivery of the new 446 candidates is handled by a signaling protocol such as SIP or XMPP. 447 Trickle ICE imposes no restrictions on the way this is done (e.g., 448 some applications may choose not to send trickle updates for server 449 reflexive candidates and instead rely on the discovery of peer 450 reflexive ones). 452 When trickle updates are sent, each candidate MUST be delivered to 453 the receiving Trickle ICE implementation not more than once. If 454 there are any candidate retransmissions, they need to be hidden from 455 the ICE implementation. 457 Also, candidate trickling needs to be correlated to a specific ICE 458 negotiation session, so that if there is an ICE restart, any delayed 459 updates for a previous session can be recognized as such and ignored 460 by the receiving party. For example, applications that choose to 461 signal candidates via SDP may include a ufrag value in the 462 corresponding a=candidate line such as: 464 a=candidate:1 1 UDP 2130706431 2001:db8::1 5000 typ host ufrag 8hhY 466 Or as another example, WebRTC implementations may include a ufrag in 467 the JavaScript objects that represent candidates. 469 Note: The signaling protocol needs to provide a mechanism for both 470 parties to indicate and agree on the ICE negotiation session in force 471 (as identified by the ufrag) so that they have a consistent view of 472 which candidates are to be paired. This is especially important in 473 the case of ICE restarts (see Section 13). 475 Once the candidate has been sent to the remote party, the agent 476 checks if any remote candidates are currently known for this same 477 stream. If not, the new candidate will simply be added to the list 478 of local candidates. 480 Otherwise, if the agent has already learned of one or more remote 481 candidates for this stream and component, it will begin pairing the 482 new local candidates with them and adding the pairs to the existing 483 check lists according to their priority. 485 Note: A Trickle ICE agent MUST NOT pair a local candidate until it 486 has been trickled to the remote agent. 488 8.1. Pairing Newly Learned Candidates and Updating Check Lists 490 Forming candidate pairs works as described in the ICE specification 491 [rfc5245bis]. However, actually adding the new pair to a check list 492 happens according to the rules described below. 494 If the check list where the pair is to be added already contains the 495 maximum number of candidate pairs (100 by default as per 496 [rfc5245bis]), the new pair is discarded. 498 If the new pair's local candidate is server reflexive, the server 499 reflexive candidate MUST be replaced by its base before adding the 500 pair to the list. 502 Once this is done, the agent examines the check list looking for 503 another pair that would be redundant with the new one. If such a 504 pair exists and the type of its remote candidate is not peer 505 reflexive, the pair with the higher priority is kept and the one with 506 the lower priority is discarded. If, on the other hand, the type of 507 the remote candidate in the pre-existing pair is peer reflexive, the 508 agent MUST replace it with the newly formed pair (regardless of their 509 respective priorities); this is done by setting the priority of the 510 new candidate to the priority of the pre-existing candidate and then 511 re-sorting the check list. 513 Note: So that both agents will have the same view of candidate 514 priorities, it is important to replacing existing pairs with 515 seemingly equivalent higher-priority ones and to always update 516 peer-reflexive candidates if equivalent alternatives are received 517 through signaling. 519 For all other pairs, including those with a server reflexive local 520 candidate that were not found to be redundant, the rules specified in 521 the following section apply. 523 8.1.1. Inserting a New Pair in a Check List 525 Consider the following tabular representation of all checklists in an 526 agent: 528 +------------+------+------+------+------+------+ 529 | | f1 | f2 | f3 | f4 | f5 | 530 +------------+------+------+------+------+------+ 531 | Audio.RTP | cp | cp | cp | | | 532 +------------+------+------+------+------+------+ 533 | Audio.RTCP | cp | cp | cp | cp | | 534 +------------+------+------+------+------+------+ 535 | Video.RTP | cp | | | | cp | 536 +------------+------+------+------+------+------+ 537 | Video.RTCP | cp | | | | cp | 538 +------------+------+------+------+------+------+ 540 Figure 1: Trickle State Updates 542 Each row in the table represents a component for a given media 543 stream. Each column represents one foundation. Each cell represents 544 one candidate pair. 546 When an agent commences ICE processing as per [rfc5245bis], it will 547 unfreeze (i.e., place in the Waiting state) the topmost candidate 548 pair in every column. Then, as the checks proceed, for each pair 549 that enters the Succeeded state the agent will unfreeze the pair that 550 is immediately underneath the pair that succeeded (e.g., if the pair 551 in column 1, row 1 succeeds then the agent will unfreeze the pair in 552 column 1, row 2). ICE also specifies that, if all the pairs in a 553 media stream for one foundation are unfrozen (e.g., column 1, rows 1 554 and 2 representing both components for the audio stream), then all of 555 the candidate pairs in the entire column are unfrozen (e.g., column 556 1, rows 3 and 4). 558 Trickle ICE preserves all of these rules. This implies that if, for 559 some reason, a Trickle agent were to begin connectivity checks with 560 all of its pairs already present, the way that pair states change is 561 indistinguishable from that of a regular ICE agent. 563 Of course, the major difference with Trickle ICE is that candidates 564 can arrive after connectivity checks have started. When this 565 happens, an agent sets the state of the newly formed pair as follows: 567 Waiting: if the newly formed pair is the topmost pair in this 568 column; 570 Waiting: if the pair immediately above the newly formed pair in 571 this column is in the Succeeded state; 573 Waiting: if there is at least one pair in this column below the row 574 of the newly formed pair whose state is either Succeeded or 575 Failed. 577 Frozen: in all other cases. 579 8.2. Announcing End of Candidates 581 Once all candidate gathering is completed or expires for a specific 582 media stream, the agent will generate an "end-of-candidates" 583 indication for that stream and send it to the remote agent via the 584 signaling channel. The exact form of the indication depends on the 585 application protocol. The indication can be sent in the following 586 ways: 588 o As part of an initiation request (which would typically be the 589 case with an initial ICE description for half trickle) 591 o Along with the last candidate an agent can send for a stream 593 o As a standalone notification (e.g., after STUN Binding requests or 594 TURN Allocate requests to a server time out and the agent has no 595 other active gatherers) 597 Sending an end-of-candidates indication in a timely manner is 598 important in order to avoid ambiguities and speed up the conclusion 599 of ICE processing. In particular: 601 o A controlled Trickle ICE agent SHOULD send an end-of-candidates 602 indication after it has completed gathering for a media stream, 603 unless ICE processing terminates before the agent has had a chance 604 to complete gathering. 606 o A controlling agent MAY conclude ICE processing prior to sending 607 end-of-candidates indications for all streams. However, it is 608 RECOMMENDED for a controlling agent to send end-of-candidates 609 indications whenever possible for the sake of consistency and to 610 keep middleboxes and controlled agents up-to-date on the state of 611 ICE processing. 613 When sending an end-of-candidates indication during trickling (rather 614 than as a part of an initial ICE description or response), it is the 615 responsibility of the using protocol to define methods for relating 616 the indication to one or more specific media streams. 618 Receiving an end-of-candidates indication enables an agent to update 619 check list states and, in case valid pairs do not exist for every 620 component in every media stream, determine that ICE processing has 621 failed. It also enables agents to speed up the conclusion of ICE 622 processing when a candidate pair has been validated but it involves 623 the use of lower-preference transports such as TURN. In such 624 situations, an implementation MAY choose to wait and see if higher- 625 priority candidates are received; in this case the end-of-candidates 626 indication provides a notification that such candidates are not 627 forthcoming. 629 An agent MAY also choose to generate an end-of-candidates indication 630 before candidate gathering has actually completed, if the agent 631 determines that gathering has continued for more than an acceptable 632 period of time. However, an agent MUST NOT send any more candidates 633 after it has sent an end-of-candidates indication. 635 When performing half trickle, an agent SHOULD send an end-of- 636 candidates indication together with its initial ICE description 637 unless it is planning to potentially send additional candidates 638 (e.g., in case the remote party turns out to support Trickle ICE). 640 After an agent sends the end-of-candidates indication, it will update 641 the state of the corresponding check list as explained in 642 Section 7.2. Past that point, an agent MUST NOT send any new 643 candidates within this ICE negotiation session. After an agent has 644 received an end-of-candidates indication, it MUST also ignore any 645 newly received candidates for that media stream or media session. 646 Therefore, adding new candidates to the negotiation is possible only 647 through an ICE restart (see Section 13). 649 This specification does not override regular ICE semantics for 650 concluding ICE processing. Therefore, even if end-of-candidates 651 indications are sent, agents will still have to go through pair 652 nomination. Also, if pairs have been nominated for components and 653 media streams, ICE processing MAY still conclude even if end-of- 654 candidates indications have not been received for all streams. 656 9. Receiving Additional Remote Candidates 658 At any time during ICE processing, a Trickle ICE agent might receive 659 new candidates from the remote agent. When this happens and no local 660 candidates are currently known for this same stream, the new remote 661 candidates are added to the list of remote candidates. 663 Otherwise, the new candidates are used for forming candidate pairs 664 with the pool of local candidates and they are added to the local 665 check lists as described in Section 8.1. 667 Once the remote agent has completed candidate gathering, it will send 668 an end-of-candidates indication. Upon receiving such an indication, 669 the local agent MUST update check list states as per Section 7.2. 670 This might lead to some check lists being marked as Failed. 672 10. Receiving an End-Of-Candidates Notification 674 When an agent receives an end-of-candidates indication for a specific 675 media stream, it will update the state of the relevant check list as 676 per Section 7.2. If the check list is still in the Active state 677 after the update, the agent will persist the fact that an end-of- 678 candidates indication has been received and take it into account in 679 future updates to the check list. 681 11. Trickle ICE and Peer Reflexive Candidates 683 Even though Trickle ICE does not explicitly modify the procedures for 684 handling peer-reflexive candidates, use of Trickle ICE can have an 685 impact on how they are processed. With Trickle ICE, it is possible 686 that server reflexive candidates can be discovered as peer reflexive 687 in cases where incoming connectivity checks are received from these 688 candidates before the trickle updates that carry them. 690 While this would certainly increase the number of cases where ICE 691 processing nominates and selects candidates discovered as peer- 692 reflexive, it does not require any change in processing. 694 It is also likely that some applications would prefer not to trickle 695 server reflexive candidates to entities that are known to be publicly 696 accessible and where sending a direct STUN binding request is likely 697 to reach the destination faster than the trickle update that travels 698 through the signaling path. 700 12. Concluding ICE Processing 702 This specification does not directly modify the procedures for ending 703 ICE processing described in Section 8 of [rfc5245bis], and Trickle 704 ICE implementations follow the same rules. 706 13. Subsequent Exchanges 708 Either agent MAY generate a subsequent ICE description at any time 709 allowed by [RFC3264]. When this happens agents will use [rfc5245bis] 710 semantics to determine whether or not the new ICE description 711 requires an ICE restart. If an ICE restart occurs, the user agents 712 can assume that Trickle ICE is still supported if support was 713 determined previously, and thus can engage in Trickle ICE behavior as 714 they would in an initial exchange of ICE descriptions where support 715 was determined through a capabilities discovery method. 717 14. Unilateral Use of Trickle ICE (Half Trickle) 719 In half trickle mode, the initiator sends a regular ICE description 720 with a full generation of candidates. This ensures that the ICE 721 description can be processed by a regular ICE responder and is mostly 722 meant for use in cases where support for Trickle ICE cannot be 723 confirmed prior to sending an initial ICE description. The initial 724 ICE description indicates support for Trickle ICE, which means the 725 responder can respond with something less than a full generation of 726 candidates and then trickle the rest. A half trickle ICE description 727 would typically contain an end-of-candidates indication, although 728 this is not mandatory because if trickle support is confirmed then 729 the initiator can choose to trickle additional candidates before it 730 sends an end-of-candidates indication. 732 The half trickle mechanism can be used in cases where there is no way 733 for an agent to verify in advance whether a remote party supports 734 Trickle ICE. Because the initial ICE description contains a full 735 generation of candidates, it can thus be handled by a regular ICE 736 agent, while still allowing a Trickle ICE agent to use the 737 optimization defined in this specification. This prevents 738 negotiation from failing in the former case while still giving 739 roughly half the Trickle ICE benefits in the latter (hence the name 740 of the mechanism). 742 Use of half trickle is only necessary during an initial exchange of 743 ICE descriptions. After both parties have received a session 744 description from their peer, they can each reliably determine Trickle 745 ICE support and use it for all subsequent exchanges. 747 In some instances, using half trickle might bring more than just half 748 the improvement in terms of user experience. This can happen when an 749 agent starts gathering candidates upon user interface cues that the 750 user will soon be initiating an interaction, such as activity on a 751 keypad or the phone going off hook. This would mean that some or all 752 of the candidate gathering could be completed before the agent 753 actually needs to send the ICE description. Because the responder 754 will be able to trickle candidates, both agents will be able to start 755 connectivity checks and complete ICE processing earlier than with 756 regular ICE and potentially even as early as with full trickle. 758 However, such anticipation is not always possible. For example, a 759 multipurpose user agent or a WebRTC web page where communication is a 760 non-central feature (e.g., calling a support line in case of a 761 problem with the main features) would not necessarily have a way of 762 distinguishing between call intentions and other user activity. In 763 such cases, using full trickle is most likely to result in an ideal 764 user experience. Even so, using half trickle would be an improvement 765 over regular ICE because it would result in a better experience for 766 responders. 768 15. Requirements for Signaling Protocols 770 In order to fully enable the use of Trickle ICE, this specification 771 defines the following requirements for signaling protocols. 773 o A signaling protocol SHOULD provide a way for parties to advertise 774 and discover support for Trickle ICE before an ICE negotiation 775 session begins (see Section 3). 777 o A signaling protocol MUST provide methods for incrementally 778 sending (i.e., "trickling") additional candidates after sending 779 the initial ICE description (see Section 8). 781 o A signaling protocol MUST provide a mechanism for both parties to 782 indicate and agree on the ICE negotiation session in force (see 783 Section 8). 785 o A signaling protocol MUST provide a way for parties to communicate 786 the end-of-candidates indication (see Section 8.2). 788 16. Example Flow 790 As an example, a typical successful Trickle ICE exchange with a 791 signaling protocol that follows the offer/answer model would look 792 this way: 794 Alice Bob 795 | Offer | 796 |---------------------------------------------->| 797 | Additional Candidates | 798 |---------------------------------------------->| 799 | | 800 | Answer | 801 |<----------------------------------------------| 802 | Additional Candidates | 803 |<----------------------------------------------| 804 | | 805 | Additional Candidates and Connectivity Checks | 806 |<--------------------------------------------->| 807 | | 808 |<=============== MEDIA FLOWS =================>| 810 Figure 2: Example 812 17. IANA Considerations 814 This specification requests no actions from IANA. 816 18. Security Considerations 818 This specification inherits most of its semantics from [rfc5245bis] 819 and as a result all security considerations described there apply to 820 Trickle ICE. 822 If the privacy implications of revealing host addresses on an 823 endpoint device are a concern, agents can generate an ICE description 824 that contains no candidates and then only trickle candidates that do 825 not reveal host addresses (e.g., relayed candidates). 827 19. Acknowledgements 829 The authors would like to thank Bernard Aboba, Flemming Andreasen, 830 Rajmohan Banavi, Taylor Brandstetter, Christer Holmberg, Jonathan 831 Lennox, Enrico Marocco, Pal Martinsen, Martin Thomson, Dale R. 832 Worley, and Brandon Williams for their reviews and suggestions on 833 improving this document. 835 20. References 836 20.1. Normative References 838 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 839 Requirement Levels", BCP 14, RFC 2119, March 1997. 841 [rfc5245bis] 842 Keranen, A., Keranen, A., and J. Rosenberg, "Interactive 843 Connectivity Establishment (ICE): A Protocol for Network 844 Address Translator (NAT) Traversal", draft-ietf-ice- 845 rfc5245bis-08 (work in progress), December 2016. 847 20.2. Informative References 849 [I-D.ietf-mmusic-trickle-ice-sip] 850 Ivov, E., Thomas, T., Marocco, E., and C. Holmberg, "A 851 Session Initiation Protocol (SIP) usage for Trickle ICE", 852 draft-ietf-mmusic-trickle-ice-sip-06 (work in progress), 853 October 2016. 855 [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., 856 and E. Lear, "Address Allocation for Private Internets", 857 BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996, 858 . 860 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 861 A., Peterson, J., Sparks, R., Handley, M., and E. 862 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 863 June 2002. 865 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 866 with Session Description Protocol (SDP)", RFC 3264, June 867 2002. 869 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 870 Description Protocol", RFC 4566, July 2006. 872 [RFC4787] Audet, F., Ed. and C. Jennings, "Network Address 873 Translation (NAT) Behavioral Requirements for Unicast 874 UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January 875 2007, . 877 [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, 878 "Session Traversal Utilities for NAT (STUN)", RFC 5389, 879 DOI 10.17487/RFC5389, October 2008, 880 . 882 [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using 883 Relays around NAT (TURN): Relay Extensions to Session 884 Traversal Utilities for NAT (STUN)", RFC 5766, April 2010. 886 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 887 Protocol (XMPP): Core", RFC 6120, March 2011. 889 [XEP-0030] 890 Hildebrand, J., Millard, P., Eatmon, R., and P. Saint- 891 Andre, "XEP-0030: Service Discovery", XEP XEP-0030, June 892 2008. 894 [XEP-0176] 895 Beda, J., Ludwig, S., Saint-Andre, P., Hildebrand, J., 896 Egan, S., and R. McQueen, "XEP-0176: Jingle ICE-UDP 897 Transport Method", XEP XEP-0176, June 2009. 899 Appendix A. Interaction with Regular ICE 901 The ICE protocol was designed to be flexible enough to work in and 902 adapt to as many network environments as possible. Despite that 903 flexibility, ICE as specified in [rfc5245bis] does not by itself 904 support trickle ICE. This section describes how trickling of 905 candidates interacts with ICE. 907 [rfc5245bis] describes the conditions required to update check lists 908 and timer states while an ICE agent is in the Running state. These 909 conditions are verified upon transaction completion and one of them 910 stipulates that: 912 If there is not a pair in the valid list for each component of the 913 media stream, the state of the check list is set to Failed. 915 This could be a problem and cause ICE processing to fail prematurely 916 in a number of scenarios. Consider the following case: 918 1. Alice and Bob are both located in different networks with Network 919 Address Translation (NAT). Alice and Bob themselves have 920 different address but both networks use the same [RFC1918] block. 922 2. Alice sends Bob the candidate 2001:db8:a0b:12f0::10 which also 923 happens to correspond to an existing host on Bob's network. 925 3. Bob creates a check list consisting solely of 926 2001:db8:a0b:12f0::10 and starts checks. 928 4. These checks reach the host at 2001:db8:a0b:12f0::10 in Bob's 929 network, which responds with an ICMP "port unreachable" error and 930 per [rfc5245bis] Bob marks the transaction as Failed. 932 At this point the check list only contains Failed candidates and the 933 valid list is empty. This causes the media stream and potentially 934 all ICE processing to fail. 936 A similar race condition would occur if the initial ICE description 937 from Alice only contains candidates that can be determined as 938 unreachable from any of the candidates that Bob has gathered (e.g., 939 this would be the case if Bob's candidates only contain IPv4 940 addresses and the first candidate that he receives from Alice is an 941 IPv6 one). 943 Another potential problem could arise when a non-trickle ICE 944 implementation initiates an interaction with a Trickle ICE 945 implementation. Consider the following case: 947 1. Alice's client has a non-Trickle ICE implementation. 949 2. Bob's client has support for Trickle ICE. 951 3. Alice and Bob are behind NATs with address-dependent filtering 952 [RFC4787]. 954 4. Bob has two STUN servers but one of them is currently 955 unreachable. 957 After Bob's agent receives Alice's initial ICE description it would 958 immediately start connectivity checks. It would also start gathering 959 candidates, which would take a long time because of the unreachable 960 STUN server. By the time Bob's answer is ready and sent to Alice, 961 Bob's connectivity checks may well have failed: until Alice gets 962 Bob's answer, she won't be able to start connectivity checks and 963 punch holes in her NAT. The NAT would hence be filtering Bob's 964 checks as originating from an unknown endpoint. 966 Appendix B. Interaction with ICE Lite 968 The behavior of ICE lite agents that are capable of Trickle ICE does 969 not require any particular rules other than those already defined in 970 this specification and [rfc5245bis]. This section is hence provided 971 only for informational purposes. 973 An ICE lite agent would generate an ICE description as per 974 [rfc5245bis] and would indicate support for Trickle ICE. Given that 975 the ICE description will contain a full generation of candidates, it 976 would also be accompanied by an end-of-candidates indication. 978 When performing full trickle, a full ICE implementation could send an 979 initial ICE description or response with no candidates. After 980 receiving a response that identifies the remote agent as an ICE lite 981 implementation, the initiator can choose to not send any additional 982 candidates. The same is also true in the case when the ICE lite 983 agent initiates the interaction and the full ICE agent is the 984 responder. In these cases the connectivity checks would be enough 985 for the ICE lite implementation to discover all potentially useful 986 candidates as peer reflexive. The following example illustrates one 987 such ICE session using SDP syntax: 989 ICE Lite Bob 990 Agent 991 | Offer (a=ice-lite a=ice-options:trickle) | 992 |---------------------------------------------->| 993 | |no cand 994 | Answer (a=ice-options:trickle) |trickling 995 |<----------------------------------------------| 996 | Connectivity Checks | 997 |<--------------------------------------------->| 998 peer rflx| | 999 cand disco| | 1000 | | 1001 |<=============== MEDIA FLOWS =================>| 1003 Figure 3: Example 1005 In addition to reducing signaling traffic this approach also removes 1006 the need to discover STUN bindings or make TURN allocations, which 1007 may considerably lighten ICE processing. 1009 Appendix C. Preserving Candidate Order while Trickling 1011 One important aspect of regular ICE is that connectivity checks for a 1012 specific foundation and component are attempted simultaneously by 1013 both agents, so that any firewalls or NATs fronting the agents would 1014 whitelist both endpoints and allow all except for the first 1015 ("suicide") packets to go through. This is also important to 1016 unfreezing candidates at the right time. While not crucial, 1017 preserving this behavior in Trickle ICE is likely to improve ICE 1018 performance. 1020 To achieve this, when trickling candidates agents MUST respect the 1021 order in which the components and streams as they have been 1022 negotiated appear (implicitly or explicitly) in the relevant ICE 1023 descriptions. Therefore a candidate for a specific component MUST 1024 NOT be sent prior to candidates for other components within the same 1025 foundation. 1027 For example, the following SDP description contains two components 1028 (RTP and RTCP) and two foundations (host and server reflexive): 1030 v=0 1031 o=jdoe 2890844526 2890842807 IN IP6 2001:db8:a0b:12f0::1 1032 s= 1033 c=IN IP4 2001:db8:a0b:12f0::1 1034 t=0 0 1035 a=ice-pwd:asd88fgpdd777uzjYhagZg 1036 a=ice-ufrag:8hhY 1037 m=audio 5000 RTP/AVP 0 1038 a=rtpmap:0 PCMU/8000 1039 a=candidate:1 1 UDP 2130706431 2001:db8:a0b:12f0::1 5000 typ host 1040 a=candidate:1 2 UDP 2130706431 2001:db8:a0b:12f0::1 5001 typ host 1041 a=candidate:2 1 UDP 1694498815 2001:db8:a0b:12f0::3 5000 typ srflx 1042 raddr 2001:db8:a0b:12f0::1 rport 8998 1043 a=candidate:2 2 UDP 1694498815 2001:db8:a0b:12f0::3 5001 typ srflx 1044 raddr 2001:db8:a0b:12f0::1 rport 8998 1046 For this description the RTCP host candidate MUST NOT be sent prior 1047 to the RTP host candidate. Similarly the RTP server reflexive 1048 candidate MUST be sent together with or prior to the RTCP server 1049 reflexive candidate. 1051 Similar considerations apply at the level of media streams in 1052 addition to foundations; this is covered by the requirement to always 1053 start unfreezing candidates starting from the first media stream as 1054 described under Section 5.2. 1056 Appendix D. Changes from Earlier Versions 1058 Note to the RFC-Editor: please remove this section prior to 1059 publication as an RFC. 1061 D.1. Changes from draft-ietf-ice-trickle-04 1063 o Removed dependency on SDP and offer/answer model. 1065 o Removed mentions of aggressive nomination, since it is deprecated 1066 in 5245bis. 1068 o Added section on requirements for signaling protocols. 1070 o Clarified terminology. 1072 o Addressed various WG feedback. 1074 D.2. Changes from draft-ietf-ice-trickle-03 1076 o Copy edit. 1078 D.3. Changes from draft-ietf-ice-trickle-03 1080 o Provided more detailed description of unfreezing behavior, 1081 specifically how to replace pre-existing peer-reflexive candidates 1082 with higher-priority ones received via trickling. 1084 D.4. Changes from draft-ietf-ice-trickle-02 1086 o Adjusted unfreezing behavior when there are disparate foundations. 1088 D.5. Changes from draft-ietf-ice-trickle-01 1090 o Changed examples to use IPv6. 1092 D.6. Changes from draft-ietf-ice-trickle-00 1094 o Removed dependency on SDP (which is to be provided in a separate 1095 specification). 1097 o Clarified text about the fact that a check list can be empty if no 1098 candidates have been sent or received yet. 1100 o Clarified wording about check list states so as not to define new 1101 states for "Active" and "Frozen" because those states are not 1102 defined for check lists (only for candidate pairs) in ICE core. 1104 o Removed open issues list because it was out of date. 1106 o Completed a thorough copy edit. 1108 D.7. Changes from draft-mmusic-trickle-ice-02 1110 o Addressed feedback from Rajmohan Banavi and Brandon Williams. 1112 o Clarified text about determining support and about how to proceed 1113 if it can be determined that the answering agent does not support 1114 Trickle ICE. 1116 o Clarified text about check list and timer updates. 1118 o Clarified when it is appropriate to use half trickle or to send no 1119 candidates in an offer or answer. 1121 o Updated the list of open issues. 1123 D.8. Changes from draft-ivov-01 and draft-mmusic-00 1125 o Added a requirement to trickle candidates by order of components 1126 to avoid deadlocks in the unfreezing algorithm. 1128 o Added an informative note on peer-reflexive candidates explaining 1129 that nothing changes for them semantically but they do become a 1130 more likely occurrence for Trickle ICE. 1132 o Limit the number of pairs to 100 to comply with 5245. 1134 o Added clarifications on the non-importance of how newly discovered 1135 candidates are trickled/sent to the remote party or if this is 1136 done at all. 1138 o Added transport expectations for trickled candidates as per Dale 1139 Worley's recommendation. 1141 D.9. Changes from draft-ivov-00 1143 o Specified that end-of-candidates is a media level attribute which 1144 can of course appear as session level, which is equivalent to 1145 having it appear in all m-lines. Also made end-of-candidates 1146 optional for cases such as aggressive nomination for controlled 1147 agents. 1149 o Added an example for ICE lite and Trickle ICE to illustrate how, 1150 when talking to an ICE lite agent doesn't need to send or even 1151 discover any candidates. 1153 o Added an example for ICE lite and Trickle ICE to illustrate how, 1154 when talking to an ICE lite agent doesn't need to send or even 1155 discover any candidates. 1157 o Added wording that explicitly states ICE lite agents have to be 1158 prepared to receive no candidates over signaling and that they 1159 should not freak out if this happens. (Closed the corresponding 1160 open issue). 1162 o It is now mandatory to use MID when trickling candidates and using 1163 m-line indexes is no longer allowed. 1165 o Replaced use of 0.0.0.0 to IP6 :: in order to avoid potential 1166 issues with RFC2543 SDP libraries that interpret 0.0.0.0 as an on- 1167 hold operation. Also changed the port number here from 1 to 9 1168 since it already has a more appropriate meaning. (Port change 1169 suggested by Jonathan Lennox). 1171 o Closed the Open Issue about use about what to do with cands 1172 received after end-of-cands. Solution: ignore, do an ICE restart 1173 if you want to add something. 1175 o Added more terminology, including trickling, trickled candidates, 1176 half trickle, full trickle, 1178 o Added a reference to the SIP usage for Trickle ICE as requested at 1179 the Boston interim. 1181 D.10. Changes from draft-rescorla-01 1183 o Brought back explicit use of Offer/Answer. There are no more 1184 attempts to try to do this in an O/A independent way. Also 1185 removed the use of ICE Descriptions. 1187 o Added SDP specification for trickled candidates, the trickle 1188 option and 0.0.0.0 addresses in m-lines, and end-of-candidates. 1190 o Support and Discovery. Changed that section to be less abstract. 1191 As discussed in IETF85, the draft now says implementations and 1192 usages need to either determine support in advance and directly 1193 use trickle, or do half trickle. Removed suggestion about use of 1194 discovery in SIP or about letting implementing protocols do what 1195 they want. 1197 o Defined Half Trickle. Added a section that says how it works. 1198 Mentioned that it only needs to happen in the first o/a (not 1199 necessary in updates), and added Jonathan's comment about how it 1200 could, in some cases, offer more than half the improvement if you 1201 can pre-gather part or all of your candidates before the user 1202 actually presses the call button. 1204 o Added a short section about subsequent offer/answer exchanges. 1206 o Added a short section about interactions with ICE Lite 1207 implementations. 1209 o Added two new entries to the open issues section. 1211 D.11. Changes from draft-rescorla-00 1213 o Relaxed requirements about verifying support following a 1214 discussion on MMUSIC. 1216 o Introduced ICE descriptions in order to remove ambiguous use of 1217 3264 language and inappropriate references to offers and answers. 1219 o Removed inappropriate assumption of adoption by RTCWEB pointed out 1220 by Martin Thomson. 1222 Authors' Addresses 1224 Emil Ivov 1225 Atlassian 1226 303 Colorado Street, #1600 1227 Austin 78701 1228 USA 1230 Phone: +1-512-640-3000 1231 Email: eivov@atlassian.com 1233 Eric Rescorla 1234 RTFM, Inc. 1235 2064 Edgewood Drive 1236 Palo Alto, CA 94303 1237 USA 1239 Phone: +1 650 678 2350 1240 Email: ekr@rtfm.com 1242 Justin Uberti 1243 Google 1244 747 6th St S 1245 Kirkland, WA 98033 1246 USA 1248 Phone: +1 857 288 8888 1249 Email: justin@uberti.name 1250 Peter Saint-Andre 1251 Filament 1252 P.O. Box 787 1253 Parker, CO 80134 1254 USA 1256 Phone: +1 720 256 6756 1257 Email: peter@filament.com 1258 URI: https://filament.com/