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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Jones 3 Internet-Draft S. Dhesikan 4 Intended status: Standards Track C. Jennings 5 Expires: September 11, 2016 Cisco Systems 6 D. Druta 7 AT&T 8 March 10, 2016 10 DSCP and other packet markings for WebRTC QoS 11 draft-ietf-tsvwg-rtcweb-qos-14 13 Abstract 15 Many networks, such as service provider and enterprise networks, can 16 provide different forwarding treatments for individual packets based 17 on Differentiated Services Code Point (DSCP) values on a per-hop 18 basis. This document provides the recommended DSCP values for web 19 browsers to use for various classes of WebRTC traffic. 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 11, 2016. 38 Copyright Notice 40 Copyright (c) 2016 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. Relation to Other Specifications . . . . . . . . . . . . . . 3 57 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 4. Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 5. DSCP Mappings . . . . . . . . . . . . . . . . . . . . . . . . 5 60 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 61 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 62 8. Downward References . . . . . . . . . . . . . . . . . . . . . 7 63 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 64 10. Dedication . . . . . . . . . . . . . . . . . . . . . . . . . 8 65 11. Document History . . . . . . . . . . . . . . . . . . . . . . 8 66 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 67 12.1. Normative References . . . . . . . . . . . . . . . . . . 8 68 12.2. Informative References . . . . . . . . . . . . . . . . . 9 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 71 1. Introduction 73 Differentiated Services Code Point (DSCP) [RFC2474] packet marking 74 can help provide QoS in some environments. This specification 75 provides default packet marking for browsers that support WebRTC 76 applications, but does not change any advice or requirements in 77 existing IETF RFCs. The contents of this specification are intended 78 to be a simple set of implementation recommendations based on the 79 previous RFCs. 81 There are many use cases where such marking does not help, but it 82 seldom makes things worse if packets are marked appropriately. There 83 are some environments where DSCP markings frequently help, though. 84 These include: 86 1. Private, wide-area networks. 88 2. Residential Networks. If the congested link is the broadband 89 uplink in a cable or DSL scenario, often residential routers/NAT 90 support preferential treatment based on DSCP. 92 3. Wireless Networks. If the congested link is a local wireless 93 network, marking may help. 95 DSCP values are in principle site specific, with each site selecting 96 its own code points for controlling per-hop-behavior to influence the 97 QoS for transport-layer flows. However in the WebRTC use cases, the 98 browsers need to set them to something when there is no site specific 99 information. In this document, "browsers" is used synonymously with 100 "Interactive User Agent" as defined in the HTML specification, 101 [W3C.REC-html5-20141028]. This document describes a subset of DSCP 102 code point values drawn from existing RFCs and common usage for use 103 with WebRTC applications. These code points are solely defaults. 105 This specification defines inputs that are provided by the WebRTC 106 application hosted in the browser that aid the browser in determining 107 how to set the various packet markings. The specification also 108 defines the mapping from abstract QoS policies (flow type, priority 109 level) to those packet markings. 111 2. Relation to Other Specifications 113 This document is a complement to [RFC7657], which describes the 114 interaction between DSCP and real-time communications. That RFC 115 covers the implications of using various DSCP values, particularly 116 focusing on Real-time Transport Protocol (RTP) [RFC3550] streams that 117 are multiplexed onto a single transport-layer flow. 119 There are a number of guidelines specified in [RFC7657] that apply to 120 marking traffic sent by WebRTC applications, as it is common for 121 multiple RTP streams to be multiplexed on the same transport-layer 122 flow. Generally, the RTP streams would be marked with a value as 123 appropriate from Table 1. A WebRTC application might also multiplex 124 data channel [I-D.ietf-rtcweb-data-channel] traffic over the same 125 5-tuple as RTP streams, which would also be marked as per that table. 126 The guidance in [RFC7657] says that all data channel traffic would be 127 marked with a single value that is typically different than the 128 value(s) used for RTP streams multiplexed with the data channel 129 traffic over the same 5-tuple, assuming RTP streams are marked with a 130 value other than default forwarding (DF). This is expanded upon 131 further in the next section. 133 This specification does not change or override the advice in any 134 other standards about setting packet markings. Rather, it simply 135 selects a subset of DSCP values that is relevant in the WebRTC 136 context. 138 The DSCP value set by the endpoint is not trusted by the network. In 139 addition, the DSCP value may be remarked at any place in the network 140 for a variety of reasons to any other DSCP value, including default 141 forwarding (DF) value to provide basic best effort service. Even so, 142 there is benefit in marking traffic even if it only benefits the 143 first few hops. The implications are discussed in Secton 3.2 of 144 [RFC7657]. Further, a mitigation for such action is through an 145 authorization mechanism. Such an authorization mechanism is outside 146 the scope of this document. 148 3. Terminology 150 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 151 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 152 document are to be interpreted as described in [RFC2119]. 154 4. Inputs 156 WebRTC applications send and receive two types of flows of 157 significance to this document: 159 o media flows which are RTP streams [I-D.ietf-rtcweb-rtp-usage] 161 o data flows which are data channels [I-D.ietf-rtcweb-data-channel] 163 Each of the RTP streams and distinct data channels consists of all of 164 the packets associated with an independent media entity, so an RTP 165 stream or distinct data channel is not always equivalent to a 166 transport-layer flow defined by a 5-tuple (source address, 167 destination address, source port, destination port, and protocol). 168 There may be multiple RTP streams and data channels multiplexed over 169 the same 5-tuple, with each having a different level of importance to 170 the application and, therefore, potentially marked using different 171 DSCP values than another RTP stream or data channel within the same 172 transport-layer flow. (Note that there are restrictions with respect 173 to marking different data channels carried within the same SCTP 174 association as outlined in Section 5.) 176 The following are the inputs provided by the WebRTC application to 177 the browser: 179 o Flow Type: The browser provides this input as it knows if the flow 180 is audio, interactive video with or without audio, non-interactive 181 video with or without audio, or data. 183 o Application Priority: Another input is the relative importance of 184 an RTP stream or data channel. Many applications have multiple 185 flows of the same Flow Type and often some flows are more 186 important than others. For example, in a video conference where 187 there are usually audio and video flows, the audio flow may be 188 more important than the video flow. JavaScript applications can 189 tell the browser whether a particular flow is high, medium, low or 190 very low importance to the application. 192 [I-D.ietf-rtcweb-transports] defines in more detail what an 193 individual flow is within the WebRTC context and priorities for media 194 and data flows. 196 5. DSCP Mappings 198 The DSCP values for each flow type of interest to WebRTC based on 199 application priority are shown in the following table. These values 200 are based on the framework and recommended values in [RFC4594]. A 201 web browser SHOULD use these values to mark the appropriate media 202 packets. More information on EF can be found in [RFC3246]. More 203 information on AF can be found in [RFC2597]. DF is default 204 forwarding which provides the basic best effort service [RFC2474]. 206 +------------------------+-------+------+-------------+-------------+ 207 | Flow Type | Very | Low | Medium | High | 208 | | Low | | | | 209 +------------------------+-------+------+-------------+-------------+ 210 | Audio | CS1 | DF | EF (46) | EF (46) | 211 | | (8) | (0) | | | 212 | | | | | | 213 | Interactive Video with | CS1 | DF | AF42, AF43 | AF41, AF42 | 214 | or without audio | (8) | (0) | (36, 38) | (34, 36) | 215 | | | | | | 216 | Non-Interactive Video | CS1 | DF | AF32, AF33 | AF31, AF32 | 217 | with or without audio | (8) | (0) | (28, 30) | (26, 28) | 218 | | | | | | 219 | Data | CS1 | DF | AF11 | AF21 | 220 | | (8) | (0) | | | 221 +------------------------+-------+------+-------------+-------------+ 223 Table 1: Recommended DSCP Values for WebRTC Applications 225 The application priority, indicated by the columns "very low", "low", 226 "Medium", and "high", signifies the relative importance of the flow 227 within the application. It is an input that the browser receives to 228 assist in selecting the DSCP value and adjusting the network 229 transport behavior. 231 The above table assumes that packets marked with CS1 are treated as 232 "less than best effort", such as the LE behavior described in 233 [RFC3662]. However, the treatment of CS1 is implementation 234 dependent. If an implementation treats CS1 as other than "less than 235 best effort", then the actual priority (or, more precisely, the per- 236 hop-behavior) of the packets may be changed from what is intended. 237 It is common for CS1 to be treated the same as DF, so applications 238 and browsers using CS1 cannot assume that CS1 will be treated 239 differently than DF [RFC7657]. However, it is also possible per 241 [RFC2474] for CS1 traffic to be given better treatment than DF, thus 242 caution should be exercised when electing to use CS1. 244 Implementers should also note that excess EF traffic is dropped. 245 This could mean that a packet marked as EF may not get through as 246 opposed to a packet marked with a different DSCP value. This is not 247 a flaw, but how excess EF traffic is intended to be treated. 249 The browser SHOULD first select the flow type of the flow. Within 250 the flow type, the relative importance of the flow SHOULD be used to 251 select the appropriate DSCP value. 253 The combination of flow type and application priority provides 254 specificity and helps in selecting the right DSCP value for the flow. 255 All packets within a flow SHOULD have the same application priority. 256 In some cases, the selected application priority cell may have 257 multiple DSCP values, such as AF41 and AF42. These offer different 258 drop precedences. The different drop precedence values provides 259 additional granularity in classifying packets within a flow. For 260 example, in a video conference, the video flow may have medium 261 application priority. If so, either AF42 or AF43 may be selected. 262 If the I-frames in the stream are more important than the P-frames, 263 then the I-frames can be marked with AF42 and the P-frames marked 264 with AF43. 266 It is worth noting that the application priority is utilized by the 267 coupled congestion control mechanism for media flows per 268 [I-D.ietf-rmcat-coupled-cc] and the SCTP scheduler for data channel 269 traffic per [I-D.ietf-rtcweb-data-channel]. 271 For reasons discussed in Section 6 of [RFC7657], if multiple flows 272 are multiplexed using a reliable transport (e.g., TCP) then all of 273 the packets for all flows multiplexed over that transport-layer flow 274 MUST be marked using the same DSCP value. Likewise, all WebRTC data 275 channel packets transmitted over an SCTP association MUST be marked 276 using the same DSCP value, regardless of how many data channels 277 (streams) exist or what kind of traffic is carried over the various 278 SCTP streams. In the event that the browser wishes to change the 279 DSCP value in use for an SCTP association, it MUST reset the SCTP 280 congestion controller after changing values. Frequent changes in the 281 DSCP value used for an SCTP association are discouraged, though, as 282 this would defeat any attempts at effectively managing congestion. 283 It should also be noted that any change in DSCP value that results in 284 a reset of the congestion controller puts the SCTP association back 285 into slow start, which may have undesirable effects on application 286 performance. 288 For the data channel traffic multiplexed over an SCTP association, it 289 is RECOMMENDED that the DSCP value selected be the one associated 290 with the highest priority requested for all data channels multiplexed 291 over the SCTP association. Likewise, when multiplexing multiple 292 flows over a TCP connection, the DCSP value selected should be the 293 one associated with the highest priority requested for all 294 multiplexed flows. 296 If a packet enters a network that has no support for a flow type- 297 application priority combination specified in Table 1 (above), then 298 the network node at the edge will remark the DSCP value based on 299 policies. This could result in the flow not getting the network 300 treatment it expects based on the original DSCP value in the packet. 301 Subsequently, if the packet enters a network that supports a larger 302 number of these combinations, there may not be sufficient information 303 in the packet to restore the original markings. Mechanisms for 304 restoring such original DSCP is outside the scope of this document. 306 In summary, DSCP marking provides neither guarantees nor promised 307 levels of service. However, DSCP marking is expected to provide a 308 statistical improvement in real-time service as a whole. The service 309 provided to a packet is dependent upon the network design along the 310 path, as well as the network conditions at every hop. 312 6. Security Considerations 314 This specification does not add any additional security implication 315 other than the normal application use of DSCP not already addressed 316 by the following specifications. For security implications on use of 317 DSCP, please refer to Section 7 of [RFC7657] and Section 6 of 318 [RFC4594]. Please also see [I-D.ietf-rtcweb-security] as an 319 additional reference. 321 7. IANA Considerations 323 This specification does not require any actions from IANA. 325 8. Downward References 327 This specification contains a downwards reference to [RFC4594]. 328 However, the parts of that RFC used by this specification are 329 sufficiently stable for this downward reference. 331 9. Acknowledgements 333 Thanks to David Black, Magnus Westerland, Paolo Severini, Jim 334 Hasselbrook, Joe Marcus, Erik Nordmark, Michael Tuexen, and Brian 335 Carpenter for their invaluable input. 337 10. Dedication 339 This document is dedicated to the memory of James Polk, a long-time 340 friend and colleague. James made important contributions to this 341 specification, including being one of its primary authors. The IETF 342 global community mourns his loss and he will be missed dearly. 344 11. Document History 346 Note to RFC Editor: Please remove this section. 348 This document was originally an individual submission in RTCWeb WG. 349 The RTCWeb working group selected it to be become a WG document. 350 Later the transport ADs requested that this be moved to the TSVWG WG 351 as that seemed to be a better match. 353 12. References 355 12.1. Normative References 357 [I-D.ietf-rtcweb-data-channel] 358 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data 359 Channels", draft-ietf-rtcweb-data-channel-13 (work in 360 progress), January 2015. 362 [I-D.ietf-rtcweb-rtp-usage] 363 Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time 364 Communication (WebRTC): Media Transport and Use of RTP", 365 draft-ietf-rtcweb-rtp-usage-25 (work in progress), June 366 2015. 368 [I-D.ietf-rtcweb-security] 369 Rescorla, E., "Security Considerations for WebRTC", draft- 370 ietf-rtcweb-security-08 (work in progress), February 2015. 372 [I-D.ietf-rtcweb-transports] 373 Alvestrand, H., "Transports for WebRTC", draft-ietf- 374 rtcweb-transports-11 (work in progress), January 2016. 376 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 377 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 378 RFC2119, March 1997, 379 . 381 [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration 382 Guidelines for DiffServ Service Classes", RFC 4594, DOI 383 10.17487/RFC4594, August 2006, 384 . 386 [RFC7657] Black, D., Ed. and P. Jones, "Differentiated Services 387 (Diffserv) and Real-Time Communication", RFC 7657, DOI 388 10.17487/RFC7657, November 2015, 389 . 391 12.2. Informative References 393 [I-D.ietf-rmcat-coupled-cc] 394 Islam, S., Welzl, M., and S. Gjessing, "Coupled congestion 395 control for RTP media", draft-ietf-rmcat-coupled-cc-00 396 (work in progress), September 2015. 398 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 399 "Definition of the Differentiated Services Field (DS 400 Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI 401 10.17487/RFC2474, December 1998, 402 . 404 [RFC2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski, 405 "Assured Forwarding PHB Group", RFC 2597, DOI 10.17487/ 406 RFC2597, June 1999, 407 . 409 [RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec, 410 J., Courtney, W., Davari, S., Firoiu, V., and D. 411 Stiliadis, "An Expedited Forwarding PHB (Per-Hop 412 Behavior)", RFC 3246, DOI 10.17487/RFC3246, March 2002, 413 . 415 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 416 Jacobson, "RTP: A Transport Protocol for Real-Time 417 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 418 July 2003, . 420 [RFC3662] Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort 421 Per-Domain Behavior (PDB) for Differentiated Services", 422 RFC 3662, DOI 10.17487/RFC3662, December 2003, 423 . 425 [W3C.REC-html5-20141028] 426 Hickson, I., Berjon, R., Faulkner, S., Leithead, T., 427 Navara, E., O'Connor, E., and S. Pfeiffer, "HTML5", 428 World Wide Web Consortium Recommendation REC- 429 html5-20141028, October 2014, 430 . 432 Authors' Addresses 434 Paul E. Jones 435 Cisco Systems 437 Email: paulej@packetizer.com 439 Subha Dhesikan 440 Cisco Systems 442 Email: sdhesika@cisco.com 444 Cullen Jennings 445 Cisco Systems 447 Email: fluffy@cisco.com 449 Dan Druta 450 AT&T 452 Email: dd5826@att.com