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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-26) exists of draft-ietf-rtcweb-rtp-usage-25 == Outdated reference: A later version (-12) exists of draft-ietf-rtcweb-security-08 == Outdated reference: A later version (-17) exists of draft-ietf-rtcweb-transports-10 ** Downref: Normative reference to an Informational RFC: RFC 4594 ** Downref: Normative reference to an Informational RFC: RFC 7657 Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). 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: July 30, 2016 Cisco Systems 6 D. Druta 7 AT&T 8 January 27, 2016 10 DSCP and other packet markings for WebRTC QoS 11 draft-ietf-tsvwg-rtcweb-qos-12 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 July 30, 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 Standards . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . . . . . 7 65 11. Document History . . . . . . . . . . . . . . . . . . . . . . 8 66 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 67 12.1. Normative References . . . . . . . . . . . . . . . . . . 8 68 12.2. Informative References . . . . . . . . . . . . . . . . . 9 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 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 Traditionally, DSCP values have been thought of as being site 96 specific, with each site selecting its own code points for 97 controlling per-hop-behavior to influence the QoS for transport-layer 98 flows. However in the WebRTC use cases, the browsers need to set 99 them to something when there is no site specific information. In 100 this document, "browsers" is used synonymously with "Interactive User 101 Agent" as defined in the HTML specification, 102 [W3C.REC-html5-20141028]. This document describes a subset of DSCP 103 code point values drawn from existing RFCs and common usage for use 104 with WebRTC applications. These code points are solely defaults. 106 This specification defines inputs that are provided by the WebRTC 107 application hosted in the browser that aid the browser in determining 108 how to set the various packet markings. The specification also 109 defines the mapping from abstract QoS policies (flow type, priority 110 level) to those packet markings. 112 2. Relation to Other Standards 114 This document is a complement to [RFC7657], which describes the 115 interaction between DSCP and real-time communications. That RFC 116 covers the implications of using various DSCP values, particularly 117 focusing on Real-time Transport Protocol (RTP) [RFC3550] streams that 118 are multiplexed onto a single transport-layer flow. 120 There are a number of guidelines specified in [RFC7657] that apply to 121 marking traffic sent by WebRTC applications, as it is common for 122 multiple RTP streams to be multiplexed on the same transport-layer 123 flow. Generally, the RTP streams would be marked with a value as 124 appropriate from Table 1. A WebRTC application might also multiplex 125 data channel [I-D.ietf-rtcweb-data-channel] traffic over the same 126 5-tuple as RTP streams, which would also be marked as per that table. 127 The guidance in [RFC7657] says that all data channel traffic would be 128 marked with a single value that is typically different than the 129 value(s) used for RTP streams multiplexed with the data channel 130 traffic over the same 5-tuple, assuming RTP streams are marked with a 131 value other than default forwarding (DF). This is expanded upon 132 further in the next section. 134 This specification does not change or override the advice in any 135 other standards about setting packet markings. Rather, it simply 136 selects a subset of DSCP values that is relevant in the WebRTC 137 context. 139 The DSCP value set by the endpoint is not trusted by the network. In 140 addition, the DSCP value may be remarked at any place in the network 141 for a variety of reasons to any other DSCP value, including default 142 forwarding (DF) value to provide basic best effort service. The 143 mitigation for such action is through an authorization mechanism. 144 Such authorization mechanism is outside the scope of this document. 146 There is benefit in marking traffic even if it only benefits the 147 first few hops. 149 3. Terminology 151 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 152 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 153 document are to be interpreted as described in [RFC2119]. 155 4. Inputs 157 WebRTC applications send and receive two types of flows of 158 significance to this document: 160 o media flows which are RTP streams [I-D.ietf-rtcweb-rtp-usage] 162 o data flows which are data channels [I-D.ietf-rtcweb-data-channel] 164 Each of the RTP streams and distinct data channels consists of all of 165 the packets associated with an independent media entity, so an RTP 166 stream or distinct data channel is not always equivalent to a 167 transport-layer flow defined by a 5-tuple (source address, 168 destination address, source port, destination port, and protocol). 169 There may be multiple RTP streams and data channels multiplexed over 170 the same 5-tuple, with each having a different level of importance to 171 the application and, therefore, potentially marked using different 172 DSCP values than another RTP stream or data channel within the same 173 transport-layer flow. (Note that there are restrictions with respect 174 to marking different data channels carried within the same SCTP 175 association as outlined in Section 5.) 177 The following are the inputs provided by the WebRTC application to 178 the browser: 180 o Flow Type: The browser provides this input as it knows if the flow 181 is audio, interactive video with or without audio, non-interactive 182 video with or without audio, or data. 184 o Application Priority: Another input is the relative importance of 185 an RTP stream or data channel. Many applications have multiple 186 flows of the same Flow Type and often some flows are more 187 important than others. For example, in a video conference where 188 there are usually audio and video flows, the audio flow may be 189 more important than the video flow. JavaScript applications can 190 tell the browser whether a particular flow is high, medium, low or 191 very low importance to the application. 193 [I-D.ietf-rtcweb-transports] defines in more detail what an 194 individual flow is within the WebRTC context and priorities for media 195 and data flows. 197 5. DSCP Mappings 199 The DSCP values for each flow type of interest to WebRTC based on 200 application priority are shown in the following table. These values 201 are based on the framework and recommended values in [RFC4594]. A 202 web browser SHOULD use these values to mark the appropriate media 203 packets. More information on EF can be found in [RFC3246]. More 204 information on AF can be found in [RFC2597]. DF is default 205 forwarding which provides the basic best effort service [RFC2474]. 207 +------------------------+-------+------+-------------+-------------+ 208 | Flow Type | Very | Low | Medium | High | 209 | | Low | | | | 210 +------------------------+-------+------+-------------+-------------+ 211 | Audio | CS1 | DF | EF (46) | EF (46) | 212 | | (8) | (0) | | | 213 | | | | | | 214 | Interactive Video with | CS1 | DF | AF42, AF43 | AF41, AF42 | 215 | or without audio | (8) | (0) | (36, 38) | (34, 36) | 216 | | | | | | 217 | Non-Interactive Video | CS1 | DF | AF32, AF33 | AF31, AF32 | 218 | with or without audio | (8) | (0) | (28, 30) | (26, 28) | 219 | | | | | | 220 | Data | CS1 | DF | AF11 | AF21 | 221 | | (8) | (0) | | | 222 +------------------------+-------+------+-------------+-------------+ 224 Table 1: Recommended DSCP Values for WebRTC Applications 226 The application priority, indicated by the columns "very low", "low", 227 "Medium", and "high", signifies the relative importance of the flow 228 within the application. It is an input that the browser receives to 229 assist it in selecting the DSCP value. Application priority does not 230 refer to priority in the network transport. 232 The above table assumes that packets marked with CS1 are treated as 233 "less than best effort". However, the treatment of CS1 is 234 implementation dependent. If an implementation treats CS1 as other 235 than "less than best effort", then the actual priority (or, more 236 precisely, the per-hop-behavior) of the packets may be changed from 237 what is intended. It is common for CS1 to be treated the same as DF, 238 so applications and browsers using CS1 cannot assume that CS1 will be 239 treated differently than DF [RFC7657]. Implementers should also note 240 that excess EF traffic is dropped. This could mean that a packet 241 marked as EF may not get through as opposed to a packet marked with a 242 different DSCP value. 244 The browser SHOULD first select the flow type of the flow. Within 245 the flow type, the relative importance of the flow SHOULD be used to 246 select the appropriate DSCP value. 248 The combination of flow type and application priority provides 249 specificity and helps in selecting the right DSCP value for the flow. 250 All packets within a flow SHOULD have the same application priority. 251 In some cases, the selected application priority cell may have 252 multiple DSCP values, such as AF41 and AF42. These offer different 253 drop precedences. The different drop precedence values provides 254 additional granularity in classifying packets within a flow. For 255 example, in a video conference, the video flow may have medium 256 application priority. If so, either AF42 or AF43 may be selected. 257 If the I-frames in the stream are more important than the P-frames, 258 then the I-frames can be marked with AF42 and the P-frames marked 259 with AF43. 261 It is worth noting that the application priority is utilized by the 262 SCTP scheduler for data channel traffic per 263 [I-D.ietf-rtcweb-data-channel]. 265 For reasons discussed in Section 6 of [RFC7657], if multiple flows 266 are multiplexed using a reliable transport (e.g., TCP) then all of 267 the packets for all flows multiplexed over that transport-layer flow 268 MUST be marked using the same DSCP value. Likewise, all WebRTC data 269 channel packets transmitted over an SCTP association MUST be marked 270 using the same DSCP value, regardless of how many data channels 271 (streams) exist or what kind of traffic is carried over the various 272 SCTP streams. In the event that the browser wishes to change the 273 DSCP value in use for an SCTP association, it MUST reset the SCTP 274 congestion controller after changing values. Frequent changes in the 275 DSCP value used for an SCTP association are discouraged, though, as 276 this would defeat any attempts at effectively managing congestion. 277 It should also be noted that any change in DSCP value that results in 278 a reset of the congestion controller puts the SCTP association back 279 into slow start, which may have undesirable effects on application 280 performance. 282 For the data channel traffic multiplexed over an SCTP association, it 283 is RECOMMENDED that the DSCP value selected be the one associated 284 with the highest priority requested for all data channels multiplexed 285 over the SCTP association. Likewise, when multiplexing multiple 286 flows over a TCP connection, the DCSP value selected should be the 287 one associated with the highest priority requested for all 288 multiplexed flows. 290 If a packet enters a network that has no support for a flow type- 291 application priority combination specified in Table 1 (above), then 292 the network node at the edge will remark the DSCP value based on 293 policies. This could result in the flow not getting the network 294 treatment it expects based on the original DSCP value in the packet. 295 Subsequently, if the packet enters a network that supports a larger 296 number of these combinations, there may not be sufficient information 297 in the packet to restore the original markings. Mechanisms for 298 restoring such original DSCP is outside the scope of this document. 300 In summary, DSCP marking provides neither guarantees nor promised 301 levels of service. The service provided to a packet is dependent 302 upon the network design along the path, as well as the network 303 conditions at every hop. 305 6. Security Considerations 307 This specification does not add any additional security implication 308 other than the normal application use of DSCP not already addressed 309 by the following specifications. For security implications on use of 310 DSCP, please refer to Section 7 of [RFC7657] and Section 6 of 311 [RFC4594]. Please also see [I-D.ietf-rtcweb-security] as an 312 additional reference. 314 7. IANA Considerations 316 This specification does not require any actions from IANA. 318 8. Downward References 320 This specification contains a downwards reference to [RFC4594]. 321 However, the parts of that RFC used by this specification are 322 sufficiently stable for this downward reference. 324 9. Acknowledgements 326 Thanks to David Black, Magnus Westerland, Paolo Severini, Jim 327 Hasselbrook, Joe Marcus, Erik Nordmark, and Michael Tuexen for their 328 invaluable input. 330 10. Dedication 332 This document is dedicated to the memory of James Polk, a long-time 333 friend and colleague. James made important contributions to this 334 specification, including being one of its primary authors. The IETF 335 global community mourns his loss and he will be missed dearly. 337 11. Document History 339 Note to RFC Editor: Please remove this section. 341 This document was originally an individual submission in RTCWeb WG. 342 The RTCWeb working group selected it to be become a WG document. 343 Later the transport ADs requested that this be moved to the TSVWG WG 344 as that seemed to be a better match. 346 12. References 348 12.1. Normative References 350 [I-D.ietf-rtcweb-data-channel] 351 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data 352 Channels", draft-ietf-rtcweb-data-channel-13 (work in 353 progress), January 2015. 355 [I-D.ietf-rtcweb-rtp-usage] 356 Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time 357 Communication (WebRTC): Media Transport and Use of RTP", 358 draft-ietf-rtcweb-rtp-usage-25 (work in progress), June 359 2015. 361 [I-D.ietf-rtcweb-security] 362 Rescorla, E., "Security Considerations for WebRTC", draft- 363 ietf-rtcweb-security-08 (work in progress), February 2015. 365 [I-D.ietf-rtcweb-transports] 366 Alvestrand, H., "Transports for WebRTC", draft-ietf- 367 rtcweb-transports-10 (work in progress), October 2015. 369 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 370 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 371 RFC2119, March 1997, 372 . 374 [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration 375 Guidelines for DiffServ Service Classes", RFC 4594, DOI 376 10.17487/RFC4594, August 2006, 377 . 379 [RFC7657] Black, D., Ed. and P. Jones, "Differentiated Services 380 (Diffserv) and Real-Time Communication", RFC 7657, DOI 381 10.17487/RFC7657, November 2015, 382 . 384 12.2. Informative References 386 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 387 "Definition of the Differentiated Services Field (DS 388 Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI 389 10.17487/RFC2474, December 1998, 390 . 392 [RFC2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski, 393 "Assured Forwarding PHB Group", RFC 2597, DOI 10.17487/ 394 RFC2597, June 1999, 395 . 397 [RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec, 398 J., Courtney, W., Davari, S., Firoiu, V., and D. 399 Stiliadis, "An Expedited Forwarding PHB (Per-Hop 400 Behavior)", RFC 3246, DOI 10.17487/RFC3246, March 2002, 401 . 403 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 404 Jacobson, "RTP: A Transport Protocol for Real-Time 405 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 406 July 2003, . 408 [W3C.REC-html5-20141028] 409 Hickson, I., Berjon, R., Faulkner, S., Leithead, T., 410 Navara, E., O'Connor, E., and S. Pfeiffer, "HTML5", 411 World Wide Web Consortium Recommendation REC- 412 html5-20141028, October 2014, 413 . 415 Authors' Addresses 417 Paul E. Jones 418 Cisco Systems 420 Email: paulej@packetizer.com 422 Subha Dhesikan 423 Cisco Systems 425 Email: sdhesika@cisco.com 426 Cullen Jennings 427 Cisco Systems 429 Email: fluffy@cisco.com 431 Dan Druta 432 AT&T 434 Email: dd5826@att.com