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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-20) exists of draft-ietf-ice-rfc5245bis-18 == Outdated reference: A later version (-21) exists of draft-ietf-ice-trickle-17 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Jennings 3 Internet-Draft S. Nandakumar 4 Intended status: Standards Track Cisco 5 Expires: September 3, 2018 March 2, 2018 7 Snowflake - A Lighweight, Asymmetric, Flexible, Receiver Driven 8 Connectivity Establishment 9 draft-jennings-dispatch-snowflake-01 11 Abstract 13 Interactive Connectivity Establishment (ICE) (RFC5245) defines 14 protocol machinery for two peers to discover each other and establish 15 connectivity in order to send and receive Media Streams. 17 This draft raises some issues inherent in the assumptions with ICE 18 and proposes a lightweight receiver driven protocol for asymmetric 19 connectivity establishment. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on September 3, 2018. 38 Copyright Notice 40 Copyright (c) 2018 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 58 4. Snowflake for connectivity establishment . . . . . . . . . . 4 59 4.1. System Components . . . . . . . . . . . . . . . . . . . . 4 60 4.2. Protocol Workings . . . . . . . . . . . . . . . . . . . . 4 61 4.3. Advantages of Snowflake . . . . . . . . . . . . . . . . . 7 62 4.3.1. Diagnostics . . . . . . . . . . . . . . . . . . . . . 7 63 4.3.2. Timing . . . . . . . . . . . . . . . . . . . . . . . 7 64 4.3.3. Asymmetric Media . . . . . . . . . . . . . . . . . . 8 65 4.3.4. Fast Start . . . . . . . . . . . . . . . . . . . . . 8 66 5. IANA Consideration . . . . . . . . . . . . . . . . . . . . . 8 67 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 68 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 69 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 70 8.1. Normative References . . . . . . . . . . . . . . . . . . 8 71 8.2. Informative References . . . . . . . . . . . . . . . . . 8 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 74 1. Introduction 76 ICE was designed over a decade ago and certain assumptions about the 77 network topology, timing considerations, application complexity have 78 drastically changed since then. Newer additions/clarifications to 79 ICE in [I-D.ietf-ice-rfc5245bis] and Trickle ICE 80 [I-D.ietf-ice-trickle] have indeed help improve its performance and 81 the way the connectivity checks are performed. 83 However, enforcing stringent global pacing requirements coupled with 84 brute force connectivity checks, tightly coupled timing dependencies 85 between the ICE agents, the need for symmetric connection setup, for 86 example, has rendered the protocol inflexible for innovation and 87 increasingly difficult to apply and debug in a dynamic network and 88 evolving application contexts. 90 This specification defines Snowflake, where, like ICE, both sides 91 gather a set of address candidates that may work for communication. 92 However, instead of both sides trying to synchronize connectivity 93 checks in time-coupled fashion, the sending side acts as a slave and 94 sends STUN packets wherever the receiving side tells it to and when 95 it is told to do so. The receiving side is free to choose whatever 96 algorithm and timing it wants to find a path that works. The sender 97 and receiver roles are reversed for media flow in the opposite 98 direction. 100 The current version of this draft builds on its original 101 instantiation submitted in year 2015 as 102 104 2. Terminology 106 In this document, the key words "MUST", "MUST NOT", "SHOULD", "SHOULD 107 NOT", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 108 2119 [RFC2119] and indicate requirement levels for compliant 109 implementations. 111 3. Problem Statement 113 ICE was developed roughly ten years ago and several things have been 114 learned that could be improved: 116 1. It is spectacularly difficult to debug and analyze failures or 117 successes in ICE or develop good automated tests. Many 118 implementations have had significant bugs for long periods of 119 time. This is further complicated by the timing dependency as 120 explained next. 122 2. It is timing dependent. It relies on both sides to to do 123 something (candidate pairing, validation) at roughly the same 124 time and that ability to do this goes down with the number of 125 interfaces and candidates being handled. Mobile interfaces, dual 126 stack agents make this situation worse. 128 3. Differences in interpretation and implementation of the protocol 129 with respect to aggressive vs normal nomination may hinder rapid 130 convergence or may end up in agents choosing suboptimal routes. 132 4. It does not discover asymmetric routes. For example UDP leaving 133 a device may work just fine even though UDP coming into that 134 device may not work at all. 136 5. Many deployments consider using a TURN/Media Router in their 137 topology today in order to support fast session start or ensuring 138 reliable connection (although with small latency overhead). At 139 the time ICE was designed it was not understood if this would be 140 too expensive or not so. ICE works without TURN but better with 141 it. 143 6. The asymmetric nature of the controlling / controlled roles has 144 caused many interoperability problems and bugs. Also Role 145 conflicts might lead to degrade connection setup depending on 146 which side gets the the controlling role. 148 7. Priorities are complicated in dual stack world and ICE is brittle 149 to changes in this part of the algorithm. Although there are 150 advises in [I-D.ietf-ice-dualstack-fairness] specification that 151 might help here. 153 4. Snowflake for connectivity establishment 155 Snowflake is a light weight, asymmetric, flexible and receiver 156 controlled protocol for end points to establish connectivity between 157 them. 159 The following subsections go into further details of its working. 161 4.1. System Components 163 A typical Snowflake operating model has the following components 165 o Sender Agent: A Software agent interested in sending data 166 stream(s) to a remote receiver. 168 o Receiver Agent: A Software agent capable of receiving data 169 stream(s). 171 o Snowflake Agent: A software agent that is expected to have a STUN 172 Client implementation at the minimum for gathering candidates and 173 performing connectivity checks. Sender/Receiver agents are 174 Snowflake agents as well. 176 o CallAgent/Backchannel: Publicly reachable Server in the cloud 177 accessible by both the Sender and the receiver agents, acts as 178 backchannel/message bus for carrying signals between the Snowflake 179 agents. 181 o STUN Server: Optional component for determining the public facing 182 transport address of an agent behind NAT. 184 o TURN Server/Media Router: Recommended component acting as media 185 relay between the agents. A TURN Server can also act as 186 backchannel in certain instantiations. 188 4.2. Protocol Workings 190 The basic principle here is, each side (Receiver Agent) is 191 responsible for discovering a viable path for it's incoming media. 192 It does so by indicating the addresses for the Sender to verify the 193 connectivity. Once a viable path is established, the Sender Agent 194 continues to transmit the media. This process deviates from ICE by 195 negating the need for agent's role (controlled vs controlling), 196 nomination procedures (aggressive vs passive) and tightly coupled 197 symmetric checklists validation. 199 As a precursor to connectivity establishment, the protocol assumes 200 that there exists a dedicated backchannel that the agents can use to 201 exchange protocol control messages. 203 The protocol starts with the Sender Agent conveying its intention to 204 send media via the backchannel to the Receiver agent. The sender 205 does so by sending a "PlaceCall" control message and populates the 206 same with the ICE candidates gathered so far. 208 On receiving the sender's intention to send media (via the 209 backchannel), the Receiver Agent proceeds with gathering the 210 candidates defined by its local policies or previous knowledge of 211 connectivity checks. The Receiver Agent then directs the Sender 212 Agent to carryout STUN connectivity checks towards the receiver by 213 sending the "DoPing" control message via the backchannel. This 214 message is populated with the candidate pair that the receiver wants 215 the sender to verify the reachability. 217 The Receiver Agent may sends multiple "DoPing" messages to the Sender 218 Agent, sending "DoPing" message per candidate pair to be tested for 219 connectivity, as deemed necessary. The order, the timing and the 220 number of candidate pairs to be tested are fully controlled by the 221 Receiver Agent's implementation. 223 On receiving the "DoPing" message with the candidate pair to be 224 tested, the Sender Agent carries out STUN ping checks on that 225 candidate pair. It does so by sending the STUN Binding Request 226 message towards the receiver over the media path (as its done with 227 ICE today). This opens up the required local pinholes and are 228 further maintained by the Sender for the duration of the session. 229 The Sender Agent also ensures that the frequency and the timing of 230 these checks respect the congestion control requirements for the 231 underlying transport. 233 On receiving the STUN Ping from the Sender Agent, the Receiver Agent 234 does the following two things: 236 1. It responds to the connectivity check on the media path by 237 sending a STUN Binding Response. 239 2. It also sends a "GotPing" control message with the details from 240 the STUN Binding Response over the backchannel to the Sender 241 Agent. This is done so that the Sender Agent can verify the 242 connectivity status results over the backchannel as well. This 243 mechanism is especially beneficial for one-sided media scenarios 244 where the Receiver Agent can't send the STUN response to the 245 sender or if the response to STUN connectivity response was lost 246 in transmission. 248 If a successful STUN Ping response was received (either via the media 249 path or the backchannel), there is a viable path for the Sender to 250 transmit the media. 252 The above set of procedures can be continuously performed during the 253 lifetime of the session as and when the Receiver Agent determines 254 better candidates for receiving the media. Such a decision is 255 totally defined by the local policies and can be performed 256 independently of the other side. 258 Below picture captures one instance of protocol exchange where the 259 Receiver Agent indicates the Sender Agent to carry out the 260 connectivity checks. One can envision multiple executions of the 261 protocol as and when receiver has updated its knowledge of addresses 262 or priorities or bandwidth availability. 264 Snowflake Information Flow (One-way Media) 265 --------------------------------------------- 267 Sender Agent CallAgent(backchannel) Receiver Agent 268 | | | 269 | | | 270 | | | 271 |(1) connect to backchannel | 272 |.................................................| 273 | | | 274 | | | 275 |Gather Sender Candidates| | 276 | | | 277 | | | 278 | | | 279 |(2) PlaceCall [Sender Candidates] | 280 |----------------------->| | 281 | | | 282 | | | 283 | |(3) PlaceCall [Sender Candidates] 284 | |----------------------->| 285 | | | 286 | | | 287 | | |Gather Receiver Candidates 288 | | | 289 | | | 290 | | | 291 | |(4) DoPing [Candidate Pair] 292 | |<-----------------------| 293 | | | 294 | | | 295 |(5) DoPing [Candidate Pair] | 296 |<-----------------------| | 297 | | | 298 | | | 299 |(6) STUN Ping (over media path) | 300 |<----------------------------------------------->| 301 | | | 302 | | | 303 | |(7) GotPing (STUN Ping Response) 304 | |<-----------------------| 305 | | | 306 | | | 307 |(8) GotPing (STUN Ping Respnse) | 308 |<-----------------------| | 309 | | | 310 | | |Repeat Steps 4-8 as needed 311 | | |for other candidate pairs 312 | | | 313 | | | 314 | | | 315 |(9) Found a viable path for sending media | 316 |.................................................| 317 | | | 318 | | | 320 4.3. Advantages of Snowflake 322 4.3.1. Diagnostics 324 This makes it very easy to see which outbound connection were sent 325 from the Sender Agent to open a pin hole. Then when the Sender asked 326 the Receiver Agent to send a test STUN Ping, the connectivity can be 327 easily verified. It becomes easier to set up a client with an 328 automated test jig that tests all the combinations and makes sure 329 they work as you only need to test receiving capability and sender 330 capability independently. 332 4.3.2. Timing 334 This more or less removes the timing complexity by allowing both 335 sides to be responsible for their own timing. If it turns out that 336 we can pace things much faster than 50ms then this allows us to take 337 advantage of that without both sides upgrading at the same time. 338 If we end up with a lot more candidates due to v6, mobile etc, this 339 removes the issue we have today where a path might have worked but 340 the two sides did not find it due to timing issues. 342 4.3.3. Asymmetric Media 344 This allows media to be sent in one direction over a path that does 345 not work in the reverse direction. 347 4.3.4. Fast Start 349 Given there exists a dedicated backchannel, this protocol can speed 350 up the media flow by using TURN server for the backchannel, for 351 example. Once either agents learns more about the candidates, each 352 can update the other side to ensure a better low latency path is used 353 for media. 355 5. IANA Consideration 357 TODO 359 6. Security Considerations 361 TODO 363 7. Acknowledgements 365 TODO 367 8. References 369 8.1. Normative References 371 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 372 Requirement Levels", BCP 14, RFC 2119, 373 DOI 10.17487/RFC2119, March 1997, . 376 8.2. Informative References 378 [I-D.ietf-ice-dualstack-fairness] 379 Martinsen, P., Reddy, T., and P. Patil, "ICE Multihomed 380 and IPv4/IPv6 Dual Stack Guidelines", draft-ietf-ice- 381 dualstack-fairness-07 (work in progress), November 2016. 383 [I-D.ietf-ice-rfc5245bis] 384 Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive 385 Connectivity Establishment (ICE): A Protocol for Network 386 Address Translator (NAT) Traversal", draft-ietf-ice- 387 rfc5245bis-18 (work in progress), February 2018. 389 [I-D.ietf-ice-trickle] 390 Ivov, E., Rescorla, E., Uberti, J., and P. Saint-Andre, 391 "Trickle ICE: Incremental Provisioning of Candidates for 392 the Interactive Connectivity Establishment (ICE) 393 Protocol", draft-ietf-ice-trickle-17 (work in progress), 394 February 2018. 396 Authors' Addresses 398 Cullen Jennings 399 Cisco 401 Email: fluffy@iii.ca 403 Suhas Nandakumar 404 Cisco 406 Email: snandaku@cisco.com