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Wu 6 Huawei 7 May 29, 2013 9 RTP Control Protocol (RTCP) Extended Report (XR) Blocks for 10 Synchronization Delay and Offset Metrics Reporting 11 draft-ietf-xrblock-rtcp-xr-synchronization-06 13 Abstract 15 This document defines two RTP Control Protocol (RTCP) Extended Report 16 (XR) Blocks that allow the reporting of synchronization delay and 17 offset metrics for use in a range of 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 November 30, 2013. 36 Copyright Notice 38 Copyright (c) 2013 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 1.1. Synchronization Delay and Offset Metrics Reporting 55 Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3 57 1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3 58 1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 3 59 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 2.1. Standards Language . . . . . . . . . . . . . . . . . . . . 4 61 3. RTP Flows Initial Synchronization Delay Report Block . . . . . 5 62 3.1. Metric Block Structure . . . . . . . . . . . . . . . . . . 5 63 3.2. Definition of Fields in RTP Flow Initial 64 Synchronization Delay Metrics Block . . . . . . . . . . . 5 65 4. RTP Flows Synchronization Offset Metrics Block . . . . . . . . 6 66 4.1. Metric Block Structure . . . . . . . . . . . . . . . . . . 7 67 4.2. Definition of Fields in RTP Flow General 68 Synchronization Offset Metrics Block . . . . . . . . . . . 7 69 5. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 9 70 5.1. SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . . 9 71 5.2. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . 9 72 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 73 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10 74 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 75 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 76 9.1. Normative References . . . . . . . . . . . . . . . . . . . 11 77 9.2. Informative References . . . . . . . . . . . . . . . . . . 11 78 Appendix A. Metrics represented using RFC6390 Template . . . . . 12 79 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 13 80 B.1. draft-ietf-xrblock-rtcp-xr-syncronization-06 . . . . . . . 13 81 B.2. draft-ietf-xrblock-rtcp-xr-syncronization-05 . . . . . . . 13 82 B.3. draft-ietf-xrblock-rtcp-xr-syncronization-04 . . . . . . . 13 83 B.4. draft-ietf-xrblock-rtcp-xr-syncronization-03 . . . . . . . 13 84 B.5. draft-ietf-xrblock-rtcp-xr-syncronization-02 . . . . . . . 13 85 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 87 1. Introduction 89 1.1. Synchronization Delay and Offset Metrics Reporting Blocks 91 This document defines two new block types to augment those defined in 92 [RFC3611], for use in a range of RTP applications. 94 The first new block type supports reporting of Initial 95 Synchronization Delay to establish multimedia session. Information 96 is recorded about time difference between the start of RTP sessions 97 and the time the RTP receiver acquires all components of RTP sessions 98 in the multimedia session [RFC6051]. 100 The second new block type supports reporting of the relative 101 synchronization offset time of two arbitrary streams (e.g., between 102 audio and video streams), with the same RTCP CNAME included in RTCP 103 SDES packets [RFC3550]. 105 These metrics belong to the class of transport level metrics defined 106 in [RFC6792]. 108 1.2. RTCP and RTCP XR Reports 110 The use of RTCP for reporting is defined in [RFC3550]. [RFC3611] 111 defined an extensible structure for reporting using an RTCP Extended 112 Report (XR). This document defines a new Extended Report block for 113 use with [RFC3550] and [RFC3611]. 115 1.3. Performance Metrics Framework 117 The RTP Monitoring Architectures [RFC6792] provides guideline for 118 reporting block format using RTCP XR. The new report block described 119 in this memo is in compliance with the monitoring architecture 120 specified in [RFC6792]. 122 1.4. Applicability 124 When joining each session in layered video sessions [RFC6190] or the 125 multimedia session, a receiver may not synchronize playout across the 126 multimedia session or layered video session until RTCP SR packets 127 have been received on all components of RTP sessions. The component 128 RTP session are referred to as each RTP session for each media type 129 in multimedia session or separate RTP session for each layer in the 130 layered video session. For multicast session, the initial 131 synchronization delay metric varies with the session bandwidth, the 132 number of members, and the number of senders in the session. The RTP 133 flow Initial synchronization delay block defined in this document can 134 be used to report such metric, i.e., the initial synchronization 135 delay to receive all the RTP streams belonging to the same multimedia 136 session or layered video session. In the absence of packet loss, the 137 initial synchronization delay equals to the average time taken to 138 receive the first RTCP packet in the RTP session with the longest 139 RTCP reporting interval. In the presence of packet loss, the media 140 synchronization should rely on the in-band mapping of RTP and NTP- 141 format timestamps [RFC6051] or wait until the reporting interval has 142 passed, and the next RTCP SR packet is sent. 144 Receivers of the RTP flow initial synchronization delay block could 145 use this metric to compare with targets (i.e., Service Level 146 Agreement or thresholds of the system) to help ensure the quality of 147 real-time application performance. 149 In an RTP multimedia session, there can be an arbitrary number of 150 streams carried in different RTP sessions, with the same RTCP CNAME. 151 These streams may be not synchronized with each other. For example, 152 one audio stream and one video stream belong to the same session, and 153 the audio stream is transmitted lagging behind video stream for 154 multiple tens of milliseconds [TR-126]. The RTP Flows 155 Synchronization Offset block can be used to report such 156 synchronization offset between video stream and audio stream. This 157 block is also applied to the case where an RTP session can contain 158 media streams with media from multiple media types. The metrics 159 defined in the RTP flows synchronization Offset block can be used by 160 network manager for trouble shooting and dealing with user experience 161 issues. 163 2. Terminology 165 2.1. Standards Language 167 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 168 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 169 document are to be interpreted as described in RFC 2119 [RFC2119]. 171 In addition, the following terms are defined: 173 Initial Synchronization Delay: 175 A multimedia session comprises a set of concurrent RTP sessions 176 among a common group of participants, using one RTP session for 177 each media type. The initial synchronization Delay is the average 178 time for receiver to synchronize all components of a multimedia 179 session [RFC6051]. 181 Synchronization Offset: 183 Synchronization between two media streams must be maintained to 184 ensure satisfactory QoE. Two media streams can be of the same or 185 different media type belonging to one RTP session or in different 186 media types belonging to one multimedia session. The 187 Synchronization Offset is the relative time difference of the two 188 media streams that need to be synchronized. 190 3. RTP Flows Initial Synchronization Delay Report Block 192 This block is sent by RTP receivers and reports Initial 193 synchronization delay beyond the information carried in the standard 194 RTCP packet format. Information is recorded about time difference 195 between the start of multimedia session and the time when the RTP 196 receiver acquires all components of RTP sessions [RFC6051] measured 197 at the receiving end of RTP stream. 199 This block needs only be exchanged occasionally, for example sent 200 once at the start of RTP session. 202 3.1. Metric Block Structure 204 The RTP Flows Initial Synchronization Delay Report Block has the 205 following format: 207 0 1 2 3 208 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 1 209 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 210 | BT=RFISD | Reserved | Block length=2 | 211 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 212 | SSRC of Source | 213 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 214 | Initial Synchronization Delay | 215 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 3.2. Definition of Fields in RTP Flow Initial Synchronization Delay 218 Metrics Block 220 Block type (BT): 8 bits 222 The RTP Flows Initial Synchronization Delay Report Block is 223 identified by the constant . 225 [Note to RFC Editor: please replace RFISD with the IANA provided 226 RTCP XR block type for this block.] 228 Reserved: 8 bits 230 This field is reserved for future definition. In the absence of 231 such a definition, the bits in this field MUST be set to zero and 232 ignored by the receiver. 234 Block length: 16 bits 236 The constant 2, in accordance with the definition of this field in 237 Section 3 of RFC 3611 [RFC3611]. 239 SSRC of source: 32 bits 241 The SSRC of the media source SHALL be set to the value of the SSRC 242 identifier carried in any arbitrary component of RTP sessions 243 belonging to the same multimedia session. 245 Initial Synchronization Delay: 32 bits 247 The average delay, expressed in units of 1/65536 seconds, from the 248 beginning of multimedia session [RFC6051] to the time when RTCP 249 packets are received on all of the components RTP sessions. It is 250 recommended that the beginning of multimedia session is chosen as 251 the time when the receiver has joined the first RTP session of the 252 multimedia session. The value of the initial synchronization 253 delay is calculated based on received RTCP SR packets or the RTP 254 header extension containing in-band mapping of RTP and NTP-format 255 timestamps [RFC6051]. If there is no packet loss, the initial 256 synchronization delay is expected to be equal to the average time 257 taken to receive the first RTCP packet in the RTP session with the 258 longest RTCP reporting interval or the average time taken to 259 receive the first RTP header extension containing in-band mapping 260 of RTP and NTP-format timestamps. 262 If the measurement is unavailable, the value of this field with 263 all bits set to 1 MUST be reported. 265 4. RTP Flows Synchronization Offset Metrics Block 267 In the RTP multimedia sessions or one RTP session, there can be an 268 arbitrary number of Media streams and each media stream (e.g., audio 269 stream or video stream) is sent in a separate RTP stream. In case of 270 one RTP session, each media stream or each medium uses different 271 SSRC. The receiver associates RTP streams to be synchronized by 272 means of RTCP CNAME contained in the RTCP Source Description (SDES) 273 packets [RFC3550]. 275 This block is sent by RTP receivers and reports synchronization 276 offset of two arbitrary RTP streams that needs to be synchronized in 277 the RTP multimedia session. Information is recorded about the 278 relative average time difference between two arbitrary RTP streams 279 (one is reporting stream, the other is reference stream) with the 280 same CNAME and measured at the receiving end of RTP stream. In order 281 to tell what the offset of reporting stream is relative to, the block 282 for reference stream with synchronization offset of zero should be 283 reported. 285 Instances of this Block refer by Synchronization source (SSRC) to the 286 separate auxiliary Measurement Information block [RFC6776] which 287 describes measurement periods in use (see [RFC6776] section 4.2). 288 This metrics block relies on the measurement period in the 289 Measurement Information block indicating the span of the report and 290 SHOULD be sent in the same compound RTCP packet as the measurement 291 information block. If the measurement period is not received in the 292 same compound RTCP packet as this Block, this Block MUST be 293 discarded. 295 4.1. Metric Block Structure 297 The RTP Flow General Synchronization Offset Report Block has the 298 following format: 300 0 1 2 3 301 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 1 302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 303 | BT=RFSO | I | Reserved | Block length=3 | 304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 305 | SSRC of source | 306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 307 | Synchronization Offset, most significant word | 308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 309 | Synchronization Offset, least significant word | 310 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 4.2. Definition of Fields in RTP Flow General Synchronization Offset 313 Metrics Block 315 Block type (BT): 8 bits 317 The RTP Flow General Synchronization Offset Report Block is 318 identified by the constant . 320 [Note to RFC Editor: please replace RFSO with the IANA provided 321 RTCP XR block type for this block.] 323 Interval Metric Flag (I): 2 bits 325 This field is used to indicate whether the Burst/Gap Discard 326 Summary Statistics metrics are Sampled, Interval or Cumulative 327 metrics: 329 I=10: Interval Duration - the reported value applies to the 330 most recent measurement interval duration between successive 331 metrics reports. 332 I=11: Cumulative Duration - the reported value applies to the 333 accumulation period characteristic of cumulative measurements. 334 I=01: Sampled Value - the reported value is a sampled 335 instantaneous value. 337 In this document, the value I=00 is the reserved value and MUST 338 NOT be used. 340 Reserved: 6 bits 342 This field is reserved for future definition. In the absence of 343 such a definition, the bits in this field MUST be set to zero and 344 MUST be ignored by the receiver. 346 Block length: 16 bits 348 The constant 3, in accordance with the definition of this field in 349 Section 3 of RFC 3611 [RFC3611]. 351 SSRC of Source: 32 bits 353 The SSRC of the media source SHALL be set to the value of the SSRC 354 identifier of the reporting RTP stream to which the XR relates. 356 Synchronization Offset: 64 bits 358 The synchronization offset of the reporting RTP stream relative to 359 the reference stream with the same CNAME. The calculation of 360 Synchronization Offset is similar to Difference D calculation in 361 the RFC3550. That is to say, if Si is the NTP timestamp from the 362 reporting RTP packet i, and Ri is the time of arrival in NTP 363 timestamp units for reporting RTP packet i, Sj is the NTP 364 timestamp from the reference RTP packet j, and Rj is the time of 365 arrival in NTP timestamp units for reference RTP packet j, then 366 the value of the synchronization offset D may be expressed as 367 D(i,j) = (Rj - Ri) - (Sj - Si) = (Rj - Sj) - (Ri - Si) 369 If in-band delivery of NTP-format timestamps is supported 370 [RFC6051], Si and Sj should be obtained directly from the RTP 371 packets where NTP timestamps are available. If not, Si and Sj 372 should be calculated from their corresponding RTP timestamps. The 373 value of the synchronization offset is represented using a 64-bit 374 signed NTP-format timestamp as defined in [RFC5905], which is 64- 375 bit signed fixed-point number with the integer part in the first 376 32 bits and the fractional part in the last 32 bits. A positive 377 value of the synchronization offset means that the reporting 378 stream leads before the reference stream, while a negative one 379 means the reporting stream lags behind the reference stream. The 380 synchronization offset of zero means the stream is the reference 381 stream. 383 If the measurement is unavailable, the value of this field with 384 all bits set to 1 MUST be reported. 386 5. SDP Signaling 388 [RFC3611] defines the use of SDP (Session Description Protocol) 389 [RFC4566] for signaling the use of XR blocks. XR blocks MAY be used 390 without prior signaling. 392 5.1. SDP rtcp-xr-attrib Attribute Extension 394 Two new parameters are defined for the two report blocks defined in 395 this document to be used with Session Description Protocol (SDP) 396 [RFC4566] using the Augmented Backus-Naur Form (ABNF) [RFC5234]. 397 They have the following syntax within the "rtcp-xr" attribute 398 [RFC3611]: 400 xr-format = xr-rfisd-block 401 / xr-rfso-block 403 xr-rfisd-block = " rtp-flow-init-syn-delay" 404 xr-rfso-block = " rtp-flow-syn-offset" 406 Refer to Section 5.1 of RFC 3611 [RFC3611] for a detailed description 407 and the full syntax of the "rtcp-xr" attribute. 409 5.2. Offer/Answer Usage 411 When SDP is used in offer-answer context, the SDP Offer/Answer usage 412 defined in [RFC3611] applies. 414 6. IANA Considerations 416 New report block types for RTCP XR are subject to IANA registration. 417 For general guidelines on IANA allocations for RTCP XR, refer to 418 Section 6.2 of [RFC3611]. 420 This document assigns two new block type values in the RTCP XR Block 421 Type Registry: 423 Name: RFISD 424 Long Name: RTP Flows Initial Synchronization Delay 425 Value 426 Reference: Section 3 428 Name: RFSO 429 Long Name: RTP Flows Synchronization Offset Metrics Block 430 Value 431 Reference: Section 4 433 This document also registers two new SDP [RFC4566] parameters for the 434 "rtcp-xr" attribute in the RTCP XR SDP Parameters Registry: 436 * "xr-rfisd " 437 * "xr-rfso" 439 The contact information for the registrations is: 441 Qin Wu 442 sunseawq@huawei.com 443 101 Software Avenue, Yuhua District 444 Nanjing, Jiangsu 210012, China 446 7. Security Considerations 448 The new RTCP XR report blocks proposed in this document introduces no 449 new security considerations beyond those described in [RFC3611]. 451 8. Acknowledgements 453 The authors would like to thank Bill Ver Steeg, David R Oran, Ali 454 Begen, Colin Perkins, Roni Even, Kevin Gross, Jing Zhao, Fernando 455 Boronat Segui, Mario Montagud Climent, Youqing Yang, Wenxiao Yu and 456 Yinliang Hu,Jonathan Lennox for their valuable comments and 457 suggestions on this document. 459 9. References 461 9.1. Normative References 463 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 464 Requirement Levels", BCP 14, RFC 2119, March 1997. 466 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 467 Jacobson, "RTP: A Transport Protocol for Real-Time 468 Applications", STD 64, RFC 3550, July 2003. 470 [RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control 471 Protocol Extended Reports (RTCP XR)", RFC 3611, 472 November 2003. 474 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 475 Description Protocol", RFC 4566, July 2006. 477 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 478 Specifications: ABNF", STD 68, RFC 5234, January 2008. 480 [RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network 481 Time Protocol Version 4: Protocol and Algorithms 482 Specification", RFC 5905, June 2010. 484 [RFC6051] Perkins, C. and T. Schierl, "Rapid Synchronisation of RTP 485 Flows", RFC 6051, November 2010. 487 [RFC6190] Wenger, S., Wang, Y., Schierl, T., and A. Eleftheriadis, 488 "RTP Payload Format for Scalable Video Coding", RFC 6190, 489 May 2011. 491 [RFC6776] Wu, Q., "Measurement Identity and information Reporting 492 using SDES item and XR Block", RFC 6776, August 2012. 494 9.2. Informative References 496 [RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New 497 Performance Metric Development", RFC 6390, October 2011. 499 [RFC6792] Wu, Q., "Guidelines for Use of the RTP Monitoring 500 Framework", RFC 6792, November 2012. 502 [TR-126] BBF Forum, "Triple-play Services Quality of Experience 503 (QoE) Requirements", December 2006. 505 [Y.1540] ITU-T, "ITU-T Rec. Y.1540, IP packet transfer and 506 availability performance parameters", November 2007. 508 Appendix A. Metrics represented using RFC6390 Template 510 RFC EDITOR NOTE: please change XXXX in [RFCXXXX] by the new RFC 511 number, when assigned. 513 a. Initial Synchronization Delay Metric 515 * Metric Name: RTP Initial Synchronization Delay 517 * Metric Description: See Section 2.1,Initial Synchronization 518 Delay term [RFCXXXX]. 520 * Method of Measurement or Calculation: See section 3.2, Initial 521 Synchronization Delay definition [RFCXXXX]. 523 * Units of Measurement: See section 3.2, Initial Synchronization 524 Delay definition [RFCXXXX]. 526 * Measurement Point(s) with Potential Measurement Domain: See 527 section 3, 1st paragraph [RFCXXXX]. 529 * Measurement Timing: See section 3, 2nd paragraph [RFCXXXX] for 530 measurement timing. 532 * Use and applications: See section 1.4 [RFCXXXX]. 534 * Reporting model: See RFC3611. 536 b. Synchronization Offset Metric 538 * Metric Name: RTP Synchronization Offset Delay 540 * Metric Description: See Section 2.1, Synchronization Offset 541 term [RFCXXXX]. 543 * Method of Measurement or Calculation: See section 4.2, Initial 544 Synchronization Delay definition [RFCXXXX]. 546 * Units of Measurement: See section 4.2, Initial Synchronization 547 Delay definition [RFCXXXX]. 549 * Measurement Point(s) with Potential Measurement Domain: See 550 section 4, 2nd paragraph [RFCXXXX]. 552 * Measurement Timing: See section 4, 3rd paragraph [RFCXXXX] for 553 measurement timing and section 4.2 [RFCXXXX] for Interval 554 Metric flag. 556 * Use and applications: See section 1.4 [RFCXXXX]. 558 * Reporting model: See RFC3611. 560 Appendix B. Change Log 562 Note to the RFC-Editor: please remove this section prior to 563 publication as an RFC. 565 B.1. draft-ietf-xrblock-rtcp-xr-syncronization-06 567 The following are the major changes compared to previous version: 569 Some Editorial changes. 571 B.2. draft-ietf-xrblock-rtcp-xr-syncronization-05 573 The following are the major changes compared to previous version: 575 Editorial changes and typo fixed. 577 B.3. draft-ietf-xrblock-rtcp-xr-syncronization-04 579 The following are the major changes compared to previous version: 581 Additional text to clarify on how to distinguish report stream 582 from reference stream. 583 Other Editorial changes. 585 B.4. draft-ietf-xrblock-rtcp-xr-syncronization-03 587 The following are the major changes compared to previous version: 589 Remove the need to signal the reference source in the 590 synchronisation offset metrics RTCP XR report. 591 Apply RFC6390 template to metrics in the appendix. 592 Other editorial changes to get inline with other XRBLOCK drafts. 594 B.5. draft-ietf-xrblock-rtcp-xr-syncronization-02 596 The following are the major changes compared to previous version: 598 Editorial change based on comments raised on the list and in the 599 IETF85 meeting 601 Authors' Addresses 603 Hitoshi Asaeda 604 National Institute of Information and Communications Technology 605 4-2-1 Nukui-Kitamachi 606 Koganei, Tokyo 184-8795 607 Japan 609 Email: asaeda@nict.go.jp 611 Rachel Huang 612 Huawei Technologies Co., Ltd. 613 101 Software Avenue, Yuhua District 614 Nanjing, Jiangsu 210012 615 China 617 Email: Rachel@huawei.com 619 Qin Wu 620 Huawei Technologies Co., Ltd. 621 101 Software Avenue, Yuhua District 622 Nanjing, Jiangsu 210012 623 China 625 Email: sunseawq@huawei.com