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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references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) == Outdated reference: A later version (-20) exists of draft-ietf-payload-flexible-fec-scheme-01 Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Audio/Video Transport Working Group V. Singh, Ed. 3 Internet-Draft callstats.io 4 Intended status: Standards Track C. Clark 5 Expires: April 22, 2016 Telchemy 6 October 20, 2015 8 RTP Control Protocol (RTCP) Extended Report (XR) Block for Independent 9 Reporting of Burst/Gap Discard Metric 10 draft-singh-xrblock-independent-burst-gap-discard-00 12 Abstract 14 This document defines an RTP Control Protocol (RTCP) Extended Report 15 (XR) block that allows the reporting of burst and gap discard metrics 16 independently of the burst and gap loss metrics for use in a range of 17 RTP applications. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on April 22, 2016. 36 Copyright Notice 38 Copyright (c) 2015 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 1.1. Burst-Gap Discard Metrics Block . . . . . . . . . . . . . 2 55 1.2. RTCP and RTCP Extended Reports . . . . . . . . . . . . . 3 56 1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3 57 1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 4 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 3. Burst/Gap Discard Metrics Block . . . . . . . . . . . . . . . 5 60 3.1. Report Block Structure . . . . . . . . . . . . . . . . . 5 61 3.2. Definition of Fields in Burst/Gap Discard Metrics Block . 5 62 3.3. Derived Metrics Based on the Reported Metrics . . . . . . 7 63 4. Considerations for Voice-over-IP Applications . . . . . . . . 8 64 5. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 8 65 5.1. SDP rtcp-xr Attribute Extension . . . . . . . . . . . . . 8 66 5.2. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . 9 67 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 68 6.1. New RTCP XR Block Type Value . . . . . . . . . . . . . . 9 69 6.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 9 70 6.3. Contact Information for Registrations . . . . . . . . . . 9 71 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 72 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9 73 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 74 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 75 10.1. Normative References . . . . . . . . . . . . . . . . . . 10 76 10.2. Informative References . . . . . . . . . . . . . . . . . 10 77 Appendix A. Metrics Represented Using the Template from RFC 6390 12 79 1. Introduction 81 1.1. Burst-Gap Discard Metrics Block 83 This document defines a new block type that extends the metrics 84 defined in [RFC7003], the metrics in this report block can be used in 85 a range of RTP applications. The new block type reports the 86 proportion of packets discarded by the jitter buffer at the receiver 87 in a burst and number of packets discarded depends on the dejitter 88 buffer algorithm implemented by the endpoint. 90 The new report block defined in this document is different from the 91 one defined in [RFC7003]. The metrics in [RFC7003] depends on the 92 metrics in the burstgap loss metric defined in [RFC6958]. 93 Consequently, an endpoint using [RFC7003] MUST report it along with 94 [RFC6958] for it to be useful. The combined usage is useful when an 95 endpoint observes correlated packet losses and discard. However, 96 when the burst of packet losses and discards do not occur 97 simultaneously, the application may prefer a concise report block 98 that just reports the burstgap of discarded packets. The report 99 block in this document provides the complete information and does not 100 require additional report blocks. That is, this block reports: the 101 total number of packets discarded, the total burst duration, and the 102 total number of bursts, all of these metrics are missing in 103 [RFC7003]. 105 This block provides information on transient network issues. Burst/ 106 gap metrics are typically used in cumulative reports; however, they 107 may also be used in interval reports (see the Interval Metric flag in 108 Section 3.2). The variation in the number of packet discard in a 109 burst affects the user experience. Based on the metrics reported in 110 the block, the sending endpoint may change the packetisation 111 interval, vary the bitrate, etc. The report may additionally be used 112 for diagnostics [RFC6792]. The metric belongs to the class of 113 transport-related end-system metrics defined in [RFC6792]. 115 The definitions of "burst", "gap", "loss", and "discard" are 116 consistent with the definitions in [RFC3611]. To accommodate the 117 range of jitter buffer algorithms and packet discard logic that may 118 be used by implementors, the method used to distinguish between 119 bursts and gaps shall use an equivalent method to that defined in 120 Section 4.7.2 of [RFC3611]. Note that reporting the specific jitter 121 buffer algorithms and/or packet discard logic is out of the scope of 122 this document. 124 1.2. RTCP and RTCP Extended Reports 126 The use of RTCP for reporting is defined in [RFC3550]. [RFC3611] 127 defined an extensible structure for reporting using an RTCP Extended 128 Report (XR). This document defines a new Extended Report block for 129 use with [RFC3550] and [RFC3611]. 131 1.3. Performance Metrics Framework 133 The Performance Metrics Framework [RFC6390] provides guidance on the 134 definition and specification of performance metrics. The RTP 135 Monitoring Framework [RFC6792] provides guidelines for reporting 136 block format using RTCP XR. The metrics block described in this 137 document is in accordance with the guidelines in [RFC6390] and 138 [RFC6792]. 140 1.4. Applicability 142 These metrics are applicable to a range of RTP applications that 143 contain de-jitter buffers [RFC5481] at the receiving end to smooth 144 variation in packet-arrival time and don't use stream repair means, 145 e.g., Forward Error Correction (FEC) 146 [I-D.ietf-payload-flexible-fec-scheme] and/or retransmission 147 [RFC4588]. 149 2. 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 RFC 2119 [RFC2119]. 155 In addition, the following terms are defined: 157 Received, Lost, and Discarded 159 A packet shall be regarded as "lost" if it fails to arrive within 160 an implementation-specific time window. A packet that arrives 161 within this time window but is too early to be played out, too 162 late to be played out, or thrown away before playout due to packet 163 duplication or redundancy shall be regarded as discarded. A 164 packet shall not be regarded as discarded if it arrives within 165 this time window but is dropped during decoding by some higher- 166 layer decoder, e.g., due to a decoding error. A packet shall be 167 classified as one of received (or OK), discarded, or lost. The 168 metric "cumulative number of packets lost" defined in [RFC3550] 169 reports a count of packets lost from the media stream (single 170 synchronization source (SSRC) within a single RTP session). 171 Similarly, the metric "number of packets discarded" defined in 172 [RFC7002] reports a count of packets discarded from the media 173 stream (single SSRC within a single RTP session) arriving at the 174 receiver. Another metric, defined in [RFC5725], is available to 175 report on packets that are not recovered by any repair techniques 176 that may be in use. Note that the term "discard" defined here 177 builds on the "discard" definition in [RFC3611] but extends the 178 concept to take into account packet duplication and reports 179 different types of discard counts [RFC7002]. 181 Bursts and Gaps 183 The terms "burst" and "gap" are used in a manner consistent with 184 that of RTCP XR [RFC3611]. RTCP XR views an RTP stream as being 185 divided into bursts, which are periods during which the discard 186 rate is high enough to cause noticeable quality degradation 187 (generally over 5 percent discard rate), and gaps, which are 188 periods during which discarded packets are infrequent and hence 189 quality is generally acceptable. 191 3. Burst/Gap Discard Metrics Block 193 Metrics in this block report on burst/gap discard in the stream 194 arriving at the RTP system. Measurements of these metrics are made 195 at the receiving end of the RTP stream. Instances of this metrics 196 block use the synchronization source (SSRC) to refer to the separate 197 auxiliary Measurement Information Block [RFC6776], which describes 198 measurement periods in use (see [RFC6776], Section 4.2). 200 This metrics block relies on the measurement period in the 201 Measurement Information Block indicating the span of the report. 202 Senders MUST send this block in the same compound RTCP packet as the 203 Measurement Information Block. Receivers MUST verify that the 204 measurement period is received in the same compound RTCP packet as 205 this metrics block. If not, this metrics block MUST be discarded. 207 3.1. Report Block Structure 209 The structure of the Burst/Gap Discard Metrics Block is as follows. 211 0 1 2 3 212 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 213 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 214 | BT=IBGD | I | resv | Block Length = 5 | 215 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 216 | SSRC of Source | 217 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 218 | Threshold | Sum of Burst Durations (ms) | 219 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 220 | Packets Discarded in Bursts | Number of | 221 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 222 | Bursts | Total Packets Expected in Bursts | 223 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 224 | Discard Count | 225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 227 Figure 1: Report Block Structure 229 3.2. Definition of Fields in Burst/Gap Discard Metrics Block 231 Block Type (BT): 8 bits 233 A Burst/Gap Discard Metrics Block is identified by the constant 234 IBGD. 236 [Note to RFC Editor: Please replace IBGD with the IANA provided 237 RTCP XR block type for this block.] 239 Interval Metric flag (I): 2 bits 241 This field is used to indicate whether the burst/gap discard 242 metrics are Sampled, Interval, or Cumulative metrics [RFC6792]: 244 I=10: Interval Duration - the reported value applies to the 245 most recent measurement interval duration between successive 246 metrics reports. 248 I=11: Cumulative Duration - the reported value applies to the 249 accumulation period characteristic of cumulative measurements. 251 I=01: Sampled Value - the reported value is a sampled 252 instantaneous value. 254 In this document, burst/gap discard metrics can only be measured 255 over definite intervals and cannot be sampled. Also, the value 256 I=00 is reserved for future use. Senders MUST NOT use the values 257 I=00 or I=01. If a block is received with I=00 or I=01, the 258 receiver MUST discard the block. 260 Reserved (resv): 6 bits 262 These bits are reserved. They MUST be set to zero by senders and 263 ignored by receivers (see [RFC6709], Section 4.2). 265 Block Length: 16 bits 267 The length of this report block in 32-bit words, minus one. For 268 the Burst/Gap Discard Metrics Block, the block length is equal to 269 5. The block MUST be discarded if the block length is set to a 270 different value. 272 SSRC of Source: 32 bits 274 As defined in Section 4.1 of [RFC3611]. 276 Threshold: 8 bits 278 The Threshold is equivalent to Gmin in [RFC3611], i.e., the number 279 of successive packets that must not be discarded prior to and 280 following a discard packet in order for this discarded packet to 281 be regarded as part of a gap. Note that the Threshold is set in 282 accordance with the Gmin calculation defined in Section 4.7.2 of 283 [RFC3611]. 285 Sum of Burst Durations (ms): 24 bits 287 The total duration of bursts of discarded packets in the period of 288 the report (Interval or Cumulative). 290 The measured value is an unsigned value. If the measured value 291 exceeds 0xFFFFFD, the value 0xFFFFFE MUST be reported to indicate 292 an over-range measurement. If the measurement is unavailable, the 293 value 0xFFFFFF MUST be reported. 295 Packets Discarded in Bursts: 24 bits 297 The total number of packets discarded during discard bursts, as 298 defined in Section 3.2 of [RFC7002]. 300 Number of Bursts: 16 bits 302 The number of discard bursts in the period of the report (Interval 303 or Cumulative). 305 The measured value is an unsigned value. If the measured value 306 exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an 307 over-range measurement. If the measurement is unavailable, the 308 value 0xFFFF MUST be reported. 310 Total Packets Expected in Bursts: 24 bits 312 The total number of packets expected during discarded bursts (that 313 is, the sum of received packets and lost packets). The metric is 314 defined in [RFC7003]. 316 Discard Count: 32 bits 318 Number of packets discarded over the period (Interval or 319 Cumulative) covered by this report, as defined in Section 3.2 of 320 [RFC7002]. 322 3.3. Derived Metrics Based on the Reported Metrics 324 The metrics described here are intended to be used in conjunction 325 with information from the Measurement Information Block [RFC6776]. 327 These metrics provide the following information relevant to 328 statistical parameters (depending on cumulative of interval 329 measures), for example: 331 o The average discarded burst size, which can be calculated by 332 dividing the metric "Packets Discarded in Bursts" with the "Number 333 of Bursts". 335 o The average burst duration, which can be calculated by dividing 336 the metric "Sum of Burst Durations (ms)" with the "Number of 337 bursts". 339 4. Considerations for Voice-over-IP Applications 341 This metrics block is applicable to a broad range of RTP 342 applications. Where the metric is used with a Voice-over-IP (VoIP) 343 application and the stream repair means is not available, the 344 following considerations apply. 346 RTCP XR views a call as being divided into bursts, which are periods 347 during which the discard rate is high enough to cause noticeable call 348 quality degradation (generally over 5 percent discard rate) and gaps, 349 which are periods during which discarded packets are infrequent and 350 hence call quality is generally acceptable. 352 If voice activity detection is used, the burst and gap duration shall 353 be determined as if silence packets had been sent, i.e., a period of 354 silence in excess of Gmin packets will terminate a burst condition. 356 The recommended value for the threshold Gmin in [RFC3611] results in 357 a burst being a period of time during which the call quality is 358 degraded to a similar extent to a typical pulse code modulation (PCM) 359 severely errored second. 361 5. SDP Signaling 363 [RFC3611] defines the use of SDP (Session Description Protocol) 364 [RFC4566] for signaling the use of XR blocks. XR blocks MAY be used 365 without prior signaling. 367 5.1. SDP rtcp-xr Attribute Extension 369 This section augments the SDP [RFC4566] attribute "rtcp-xr" defined 370 in [RFC3611] by providing an additional value of "xr-format" to 371 signal the use of the report block defined in this document. The 372 ABNF [RFC5234] syntax is as follows. 374 xr-format =/ xr-ind-bgd-block 376 xr-ind-bgd-block = "ind-burst-gap-discard" 378 5.2. Offer/Answer Usage 380 When SDP is used in Offer/Answer context, the SDP Offer/Answer usage 381 defined in [RFC3611] for unilateral "rtcp-xr" attribute parameters 382 applies. For detailed usage in Offer/Answer for unilateral 383 parameters, refer to Section 5.2 of [RFC3611]. 385 6. IANA Considerations 387 New block types for RTCP XR are subject to IANA registration. For 388 general guidelines on IANA considerations for RTCP XR, refer to 389 [RFC3611]. 391 6.1. New RTCP XR Block Type Value 393 This document assigns the block type value IBGD in the IANA "RTP 394 Control Protocol Extended Reports (RTCP XR) Block Type Registry" to 395 the "Burst/Gap Discard Metrics Block". 397 [Note to RFC Editor: Please replace IBGD with the IANA provided RTCP 398 XR block type for this block.] 400 6.2. New RTCP XR SDP Parameter 402 This document also registers a new parameter "ind-burst-gap-discard" 403 in the "RTP Control Protocol Extended Reports (RTCP XR) Session 404 Description Protocol (SDP) Parameters Registry". 406 6.3. Contact Information for Registrations 408 The contact information for the registrations is: 410 RAI Area Directors 412 7. Security Considerations 414 It is believed that this RTCP XR block introduces no new security 415 considerations beyond those described in [RFC3611]. This block does 416 not provide per-packet statistics, so the risk to confidentiality 417 documented in Section 7, paragraph 3 of [RFC3611] does not apply. 419 8. Contributors 421 Qin Wu, Rachel Adams, and Alan Clark wrote the initial draft of this 422 document. 424 9. Acknowledgments 426 The authors acknowledge the reviews and feedback provided by various 427 people. 429 10. References 431 10.1. Normative References 433 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 434 Requirement Levels", BCP 14, RFC 2119, March 1997. 436 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 437 Jacobson, "RTP: A Transport Protocol for Real-Time 438 Applications", STD 64, RFC 3550, July 2003. 440 [RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control 441 Protocol Extended Reports (RTCP XR)", RFC 3611, November 442 2003. 444 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 445 Description Protocol", RFC 4566, July 2006. 447 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 448 Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/ 449 RFC5234, January 2008, 450 . 452 [RFC5725] Begen, A., Hsu, D., and M. Lague, "Post-Repair Loss RLE 453 Report Block Type for RTP Control Protocol (RTCP) Extended 454 Reports (XRs)", RFC 5725, February 2010. 456 [RFC6776] Clark, A. and Q. Wu, "Measurement Identity and Information 457 Reporting Using a Source Description (SDES) Item and an 458 RTCP Extended Report (XR) Block", RFC 6776, October 2012. 460 10.2. Informative References 462 [I-D.ietf-payload-flexible-fec-scheme] 463 Singh, V., Begen, A., Zanaty, M., and G. Mandyam, "RTP 464 Payload Format for Flexible Forward Error Correction 465 (FEC)", draft-ietf-payload-flexible-fec-scheme-01 (work in 466 progress), October 2015. 468 [RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. 469 Hakenberg, "RTP Retransmission Payload Format", RFC 4588, 470 July 2006. 472 [RFC5481] Morton, A. and B. Claise, "Packet Delay Variation 473 Applicability Statement", RFC 5481, DOI 10.17487/RFC5481, 474 March 2009, . 476 [RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New 477 Performance Metric Development", BCP 170, RFC 6390, 478 October 2011. 480 [RFC6709] Carpenter, B., Aboba, B., Ed., and S. Cheshire, "Design 481 Considerations for Protocol Extensions", RFC 6709, DOI 482 10.17487/RFC6709, September 2012, 483 . 485 [RFC6792] Wu, Q., Ed., Hunt, G., and P. Arden, "Guidelines for Use 486 of the RTP Monitoring Framework", RFC 6792, DOI 10.17487/ 487 RFC6792, November 2012, 488 . 490 [RFC6958] Clark, A., Zhang, S., Zhao, J., and Q. Wu, "RTP Control 491 Protocol (RTCP) Extended Report (XR) Block for Burst/Gap 492 Loss Metric Reporting", RFC 6958, May 2013. 494 [RFC7002] Clark, A., Zorn, G., and Q. Wu, "RTP Control Protocol 495 (RTCP) Extended Report (XR) Block for Discard Count Metric 496 Reporting", RFC 7002, September 2013. 498 [RFC7003] Clark, A., Huang, R., and Q. Wu, "RTP Control Protocol 499 (RTCP) Extended Report (XR) Block for Burst/Gap Discard 500 Metric Reporting", RFC 7003, September 2013. 502 Appendix A. Metrics Represented Using the Template from RFC 6390 504 a. Threshold Metric 506 * Defined in Appenix A.a of [RFC7003]. 508 b. Sum of burst durations (ms) 510 * Metric Name: Sum of Burst Durations with Discarded RTP 511 Packets. 513 * Metric Description: The total duration of bursts of discarded 514 RTP packets in the period of the report. 516 * Method of Measurement or Calculation: See Section 3.1, Sum of 517 Burst Durations definition. 519 * Units of Measurement: See Section 3.1, Sum of Burst Durations 520 definition. 522 * Measurement Point(s) with Potential Measurement Domain: See 523 Section 3, 1st paragraph. 525 * Measurement Timing: See Section 3, 2nd paragraph for 526 measurement timing and Section 3.1 for Interval Metric flag. 528 * Use and Applications: See Section 1.4. 530 * Reporting Model: See RFC 3611. 532 c. Packets Discarded in Bursts Metric 534 * Defined in Appenix A.b of [RFC7003]. 536 d. Number of bursts 538 * Metric Name: Number of discard bursts in RTP. 540 * Metric Description: The total number of bursts with discarded 541 RTP packets in the period of the report. 543 * Method of Measurement or Calculation: See Section 3.1, Number 544 of discard bursts definition. 546 * Units of Measurement: See Section 3.1 for the Number of bursts 547 definition. 549 * Measurement Point(s) with Potential Measurement Domain: See 550 Section 3, 1st paragraph. 552 * Measurement Timing: See Section 3, 2nd paragraph for 553 measurement timing and Section 3.1 for Interval Metric flag. 555 * Use and Applications: See Section 1.4. 557 * Reporting Model: See RFC 3611. 559 e. Total Packets Expected in Bursts Metric 561 * Defined in Appenix A.c of [RFC7003]. 563 f. Discard Count 565 * Defined in Appenix A.a of [RFC7002]. 567 Authors' Addresses 569 Varun Singh (editor) 570 Nemu Dialogue Systems Oy 571 Runeberginkatu 4c A 4 572 Helsinki 00100 573 Finland 575 EMail: varun@callstats.io 576 URI: http://www.callstats.io/ 578 Colin Perkins 579 University of Glasgow 580 School of Computing Science 581 Glasgow G12 8QQ 582 United Kingdom 584 EMail: csp@csperkins.org