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Wu 6 Huawei 7 May 24, 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-05 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 25, 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-05 . . . . . . . 13 81 B.2. draft-ietf-xrblock-rtcp-xr-syncronization-04 . . . . . . . 13 82 B.3. draft-ietf-xrblock-rtcp-xr-syncronization-03 . . . . . . . 13 83 B.4. draft-ietf-xrblock-rtcp-xr-syncronization-02 . . . . . . . 13 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 86 1. Introduction 88 1.1. Synchronization Delay and Offset Metrics Reporting Blocks 90 This document defines two new block types to augment those defined in 91 [RFC3611], for use in a range of RTP applications. 93 The first new block type supports reporting of Initial 94 Synchronization Delay to establish multimedia session. Information 95 is recorded about time difference between the start of RTP sessions 96 and the time the RTP receiver acquires all components of RTP sessions 97 in the multimedia session [RFC6051]. 99 The second new block type supports reporting of the relative 100 synchronization offset time of two arbitrary streams (e.g., between 101 audio and video streams), with the same RTCP CNAME included in RTCP 102 SDES packets [RFC3550]. 104 These metrics belong to the class of transport level metrics defined 105 in [RFC6792]. 107 1.2. RTCP and RTCP XR Reports 109 The use of RTCP for reporting is defined in [RFC3550]. [RFC3611] 110 defined an extensible structure for reporting using an RTCP Extended 111 Report (XR). This document defines a new Extended Report block for 112 use with [RFC3550] and [RFC3611]. 114 1.3. Performance Metrics Framework 116 The RTP Monitoring Architectures [RFC6792] provides guideline for 117 reporting block format using RTCP XR. The new report block described 118 in this memo is in compliance with the monitoring architecture 119 specified in [RFC6792]. 121 1.4. Applicability 123 When joining each session in layered video sessions [RFC6190] or the 124 multimedia session, a receiver may not synchronize playout across the 125 multimedia session or layered video session until RTCP SR packets 126 have been received on all components of RTP sessions. The component 127 RTP session are referred to as each RTP session for each media type 128 in multimedia session or separate RTP session for each layer in the 129 layered video session. For multicast session, the initial 130 synchronization delay metric varies with the session bandwidth, the 131 number of members, and the number of senders in the session. The RTP 132 flow Initial synchronization delay block defined in this document can 133 be used to report such metric, i.e., the initial synchronization 134 delay to receive all the RTP streams belonging to the same multimedia 135 session or layered video session. In the absence of packet loss, the 136 initial synchronization delay equals to the average time taken to 137 receive the first RTCP packet in the RTP session with the longest 138 RTCP reporting interval. In the presence of packet loss, the media 139 synchronization should rely on the in-band mapping of RTP and NTP- 140 format timestamps [RFC6051] or wait until the reporting interval has 141 passed, and the next RTCP SR packet is sent. 143 Receivers of the RTP flow initial synchronization delay block could 144 use this metric to compare with targets (i.e., Service Level 145 Agreement or thresholds of the system) to help ensure the quality of 146 real-time application performance. 148 In an RTP multimedia session, there can be an arbitrary number of 149 streams carried in different RTP sessions, with the same RTCP CNAME. 150 These streams may be not synchronized with each other. For example, 151 one audio stream and one video stream belong to the same session, and 152 the audio stream is transmitted lagging behind video stream for 153 multiple tens of milliseconds [TR-126]. The RTP Flows 154 Synchronization Offset block can be used to report such 155 synchronization offset between video stream and audio stream. This 156 block is also applied to the case where an RTP session can contain 157 media streams with media from multiple media types. The metrics 158 defined in the RTP flows synchronization Offset block can be used by 159 network manager for trouble shooting and dealing with user experience 160 issues. 162 2. Terminology 164 2.1. Standards Language 166 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 167 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 168 document are to be interpreted as described in RFC 2119 [RFC2119]. 170 In addition, the following terms are defined: 172 Initial Synchronization Delay: 174 A multimedia session comprises a set of concurrent RTP sessions 175 among a common group of participants, using one RTP session for 176 each media type. The initial synchronization Delay is the average 177 time for receiver to synchronize all components of a multimedia 178 session [RFC6051]. 180 Synchronization Offset: 182 Synchronization between two media streams must be maintained to 183 ensure satisfactory QoE. Two media streams can be of the same or 184 different media type belonging to one RTP session or in different 185 media types belonging to one multimedia session. The 186 Synchronization Offset is the relative time difference of the two 187 media streams that need to be synchronized. 189 3. RTP Flows Initial Synchronization Delay Report Block 191 This block is sent by RTP receivers and reports Initial 192 synchronization delay beyond the information carried in the standard 193 RTCP packet format. Information is recorded about time difference 194 between the start of multimedia session and the time when the RTP 195 receiver acquires all components of RTP sessions [RFC6051] measured 196 at the receiving end of RTP stream. 198 This block needs only be exchanged occasionally, for example sent 199 once at the start of RTP session. 201 3.1. Metric Block Structure 203 The RTP Flows Initial Synchronization Delay Report Block has the 204 following format: 206 0 1 2 3 207 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 1 208 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 209 | BT=RFISD | Reserved | Block length=2 | 210 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 211 | SSRC of Source | 212 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 213 | Initial Synchronization Delay | 214 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 216 3.2. Definition of Fields in RTP Flow Initial Synchronization Delay 217 Metrics Block 219 Block type (BT): 8 bits 221 The RTP Flows Initial Synchronization Delay Report Block is 222 identified by the constant . 224 Reserved: 8 bits 226 This field is reserved for future definition. In the absence of 227 such a definition, the bits in this field MUST be set to zero and 228 ignored by the receiver. 230 Block length: 16 bits 232 The constant 2, in accordance with the definition of this field in 233 Section 3 of RFC 3611 [RFC3611]. 235 SSRC of source: 32 bits 237 The SSRC of the media source SHALL be set to the value of the SSRC 238 identifier carried in any arbitrary component of RTP sessions 239 belonging to the same multimedia session. 241 Initial Synchronization Delay: 32 bits 243 The average delay, expressed in units of 1/65536 seconds, from the 244 beginning of multimedia session [RFC6051] to the time when RTCP 245 packets are received on all of the components RTP sessions. It is 246 recommended that the beginning of multimedia session is chosen as 247 the time when the receiver has joined the first RTP session of the 248 multimedia session. The value of the initial synchronization 249 delay is calculated based on received RTCP SR packets or the RTP 250 header extension containing in-band mapping of RTP and NTP-format 251 timestamps [RFC6051]. If there is no packet loss, the initial 252 synchronization delay is expected to be equal to the average time 253 taken to receive the first RTCP packet in the RTP session with the 254 longest RTCP reporting interval or the average time taken to 255 receive the first RTP header extension containing in-band mapping 256 of RTP and NTP-format timestamps. 258 If the measurement is unavailable, the value of this field with 259 all bits set to 1 MUST be reported. 261 4. RTP Flows Synchronization Offset Metrics Block 263 In the RTP multimedia sessions or one RTP session, there can be an 264 arbitrary number of Media streams and each media stream (e.g., audio 265 stream or video stream) is sent in a separate RTP stream. In case of 266 one RTP session, each media stream or each medium uses different 267 SSRC. The receiver associates RTP streams to be synchronized by 268 means of RTCP CNAME contained in the RTCP Source Description (SDES) 269 packets [RFC3550]. 271 This block is sent by RTP receivers and reports synchronization 272 offset of two arbitrary RTP streams that needs to be synchronized in 273 the RTP multimedia session. Information is recorded about the 274 relative average time difference between two arbitrary RTP streams 275 (one is reporting stream, the other is reference stream) with the 276 same CNAME and measured at the receiving end of RTP stream. In order 277 to tell what the offset of reporting stream is relative to, the block 278 for reference stream with synchronization offset of zero should be 279 reported. 281 Instances of this Block refer by Synchronization source (SSRC) to the 282 separate auxiliary Measurement Information block [RFC6776] which 283 describes measurement periods in use (see [RFC6776] section 4.2). 284 This metrics block relies on the measurement period in the 285 Measurement Information block indicating the span of the report and 286 SHOULD be sent in the same compound RTCP packet as the measurement 287 information block. If the measurement period is not received in the 288 same compound RTCP packet as this Block, this Block MUST be 289 discarded. 291 4.1. Metric Block Structure 293 The RTP Flow General Synchronization Offset Report Block has the 294 following format: 296 0 1 2 3 297 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 1 298 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 299 | BT=RFSO | I | Reserved | Block length=3 | 300 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 301 | SSRC of source | 302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 303 | Synchronization Offset, most significant word | 304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 305 | Synchronization Offset, least significant word | 306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 308 4.2. Definition of Fields in RTP Flow General Synchronization Offset 309 Metrics Block 311 Block type (BT): 8 bits 313 The RTP Flow General Synchronization Offset Report Block is 314 identified by the constant . 316 Interval Metric Flag (I): 2 bits 318 This field is used to indicate whether the Burst/Gap Discard 319 Summary Statistics metrics are Sampled, Interval or Cumulative 320 metrics: 322 I=10: Interval Duration - the reported value applies to the 323 most recent measurement interval duration between successive 324 metrics reports. 325 I=11: Cumulative Duration - the reported value applies to the 326 accumulation period characteristic of cumulative measurements. 327 I=01: Sampled Value - the reported value is a sampled 328 instantaneous value. 330 In this document, the value I=00 is the reserved value and MUST 331 NOT be used. 333 Reserved: 6 bits 335 This field is reserved for future definition. In the absence of 336 such a definition, the bits in this field MUST be set to zero and 337 MUST be ignored by the receiver. 339 Block length: 16 bits 341 The constant 3, in accordance with the definition of this field in 342 Section 3 of RFC 3611 [RFC3611]. 344 SSRC of Source: 32 bits 346 The SSRC of the media source SHALL be set to the value of the SSRC 347 identifier of the reporting RTP stream to which the XR relates. 349 Synchronization Offset: 64 bits 351 The synchronization offset of the reporting RTP stream relative to 352 the reference stream with the same CNAME. The calculation of 353 Synchronization Offset is similar to Difference D calculation in 354 the RFC3550. That is to say, if Si is the NTP timestamp from the 355 reporting RTP packet i, and Ri is the time of arrival in NTP 356 timestamp units for reporting RTP packet i, Sj is the NTP 357 timestamp from the reference RTP packet j, and Rj is the time of 358 arrival in NTP timestamp units for reference RTP packet j, then 359 the value of the synchronization offset D may be expressed as 360 D(i,j) = (Rj - Ri) - (Sj - Si) = (Rj - Sj) - (Ri - Si) 362 If in-band delivery of NTP-format timestamps is supported 363 [RFC6051], Si and Sj should be obtained directly from the RTP 364 packets where NTP timestamps are available. If not, Si and Sj 365 should be calculated from their corresponding RTP timestamps. The 366 value of the synchronization offset is represented using a 64-bit 367 signed NTP-format timestamp as defined in [RFC5905], which is 64- 368 bit signed fixed-point number with the integer part in the first 369 32 bits and the fractional part in the last 32 bits. A positive 370 value of the synchronization offset means that the reporting 371 stream leads before the reference stream, while a negative one 372 means the reporting stream lags behind the reference stream. The 373 synchronization offset of zero means the stream is the reference 374 stream. 376 If the measurement is unavailable, the value of this field with 377 all bits set to 1 MUST be reported. 379 5. SDP Signaling 381 [RFC3611] defines the use of SDP (Session Description Protocol) 382 [RFC4566] for signaling the use of XR blocks. XR blocks MAY be used 383 without prior signaling. 385 5.1. SDP rtcp-xr-attrib Attribute Extension 387 Two new parameters are defined for the two report blocks defined in 388 this document to be used with Session Description Protocol (SDP) 389 [RFC4566] using the Augmented Backus-Naur Form (ABNF) [RFC5234]. 390 They have the following syntax within the "rtcp-xr" attribute 391 [RFC3611]: 393 xr-format = xr-rfisd-block 394 / xr-rfso-block 396 xr-rfisd-block = " rtp-flow-init-syn-delay" 397 xr-rfso-block = " rtp-flow-syn-offset" 399 Refer to Section 5.1 of RFC 3611 [RFC3611] for a detailed description 400 and the full syntax of the "rtcp-xr" attribute. 402 5.2. Offer/Answer Usage 404 When SDP is used in offer-answer context, the SDP Offer/Answer usage 405 defined in [RFC3611] applies. 407 6. IANA Considerations 409 New report block types for RTCP XR are subject to IANA registration. 410 For general guidelines on IANA allocations for RTCP XR, refer to 411 Section 6.2 of [RFC3611]. 413 This document assigns two new block type values in the RTCP XR Block 414 Type Registry: 416 Name: RFISD 417 Long Name: RTP Flows Initial Synchronization Delay 418 Value 419 Reference: Section 3 421 Name: RFSO 422 Long Name: RTP Flows Synchronization Offset Metrics Block 423 Value 424 Reference: Section 4 426 This document also registers two new SDP [RFC4566] parameters for the 427 "rtcp-xr" attribute in the RTCP XR SDP Parameters Registry: 429 * "xr-rfisd " 430 * "xr-rfso" 432 The contact information for the registrations is: 434 Qin Wu 435 sunseawq@huawei.com 436 101 Software Avenue, Yuhua District 437 Nanjing, Jiangsu 210012, China 439 7. Security Considerations 441 The new RTCP XR report blocks proposed in this document introduces no 442 new security considerations beyond those described in [RFC3611]. 444 8. Acknowledgements 446 The authors would like to thank Bill Ver Steeg, David R Oran, Ali 447 Begen, Colin Perkins, Roni Even, Kevin Gross, Jing Zhao, Fernando 448 Boronat Segui, Mario Montagud Climent, Youqing Yang, Wenxiao Yu and 449 Yinliang Hu,Jonathan Lennox for their valuable comments and 450 suggestions on this document. 452 9. References 454 9.1. Normative References 456 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 457 Requirement Levels", BCP 14, RFC 2119, March 1997. 459 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 460 Jacobson, "RTP: A Transport Protocol for Real-Time 461 Applications", STD 64, RFC 3550, July 2003. 463 [RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control 464 Protocol Extended Reports (RTCP XR)", RFC 3611, 465 November 2003. 467 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 468 Description Protocol", RFC 4566, July 2006. 470 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 471 Specifications: ABNF", STD 68, RFC 5234, January 2008. 473 [RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network 474 Time Protocol Version 4: Protocol and Algorithms 475 Specification", RFC 5905, June 2010. 477 [RFC6051] Perkins, C. and T. Schierl, "Rapid Synchronisation of RTP 478 Flows", RFC 6051, November 2010. 480 [RFC6190] Wenger, S., Wang, Y., Schierl, T., and A. Eleftheriadis, 481 "RTP Payload Format for Scalable Video Coding", RFC 6190, 482 May 2011. 484 [RFC6776] Wu, Q., "Measurement Identity and information Reporting 485 using SDES item and XR Block", RFC 6776, August 2012. 487 9.2. Informative References 489 [RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New 490 Performance Metric Development", RFC 6390, October 2011. 492 [RFC6792] Wu, Q., "Guidelines for Use of the RTP Monitoring 493 Framework", RFC 6792, November 2012. 495 [TR-126] BBF Forum, "Triple-play Services Quality of Experience 496 (QoE) Requirements", December 2006. 498 [Y.1540] ITU-T, "ITU-T Rec. Y.1540, IP packet transfer and 499 availability performance parameters", November 2007. 501 Appendix A. Metrics represented using RFC6390 Template 503 RFC EDITOR NOTE: please change XXXX in [RFCXXXX] by the new RFC 504 number, when assigned. 506 a. Initial Synchronization Delay Metric 508 * Metric Name: RTP Initial Synchronization Delay 510 * Metric Description: See Section 2.1,Initial Synchronization 511 Delay term [RFCXXXX]. 513 * Method of Measurement or Calculation: See section 3.2, Initial 514 Synchronization Delay definition [RFCXXXX]. 516 * Units of Measurement: See section 3.2, Initial Synchronization 517 Delay definition [RFCXXXX]. 519 * Measurement Point(s) with Potential Measurement Domain: See 520 section 3, 1st paragraph [RFCXXXX]. 522 * Measurement Timing: See section 3, 2nd paragraph [RFCXXXX] for 523 measurement timing. 525 * Use and applications: See section 1.4 [RFCXXXX]. 527 * Reporting model: See RFC3611. 529 b. Synchronization Offset Metric 531 * Metric Name: RTP Synchronization Offset Delay 533 * Metric Description: See Section 2.1, Synchronization Offset 534 term [RFCXXXX]. 536 * Method of Measurement or Calculation: See section 4.2, Initial 537 Synchronization Delay definition [RFCXXXX]. 539 * Units of Measurement: See section 4.2, Initial Synchronization 540 Delay definition [RFCXXXX]. 542 * Measurement Point(s) with Potential Measurement Domain: See 543 section 4, 2nd paragraph [RFCXXXX]. 545 * Measurement Timing: See section 4, 3rd paragraph [RFCXXXX] for 546 measurement timing and section 4.2 [RFCXXXX] for Interval 547 Metric flag. 549 * Use and applications: See section 1.4 [RFCXXXX]. 551 * Reporting model: See RFC3611. 553 Appendix B. Change Log 555 Note to the RFC-Editor: please remove this section prior to 556 publication as an RFC. 558 B.1. draft-ietf-xrblock-rtcp-xr-syncronization-05 560 The following are the major changes compared to previous version: 562 Editorial changes and typo fixed. 564 B.2. draft-ietf-xrblock-rtcp-xr-syncronization-04 566 The following are the major changes compared to previous version: 568 Additional text to clarify on how to distinguish report stream 569 from reference stream. 570 Other Editorial changes. 572 B.3. draft-ietf-xrblock-rtcp-xr-syncronization-03 574 The following are the major changes compared to previous version: 576 Remove the need to signal the reference source in the 577 synchronisation offset metrics RTCP XR report. 578 Apply RFC6390 template to metrics in the appendix. 579 Other editorial changes to get inline with other XRBLOCK drafts. 581 B.4. draft-ietf-xrblock-rtcp-xr-syncronization-02 583 The following are the major changes compared to previous version: 585 Editorial change based on comments raised on the list and in the 586 IETF85 meeting 588 Authors' Addresses 590 Hitoshi Asaeda 591 National Institute of Information and Communications Technology 592 4-2-1 Nukui-Kitamachi 593 Koganei, Tokyo 184-8795 594 Japan 596 Email: asaeda@nict.go.jp 598 Rachel Huang 599 Huawei Technologies Co., Ltd. 600 101 Software Avenue, Yuhua District 601 Nanjing, Jiangsu 210012 602 China 604 Email: Rachel@huawei.com 606 Qin Wu 607 Huawei Technologies Co., Ltd. 608 101 Software Avenue, Yuhua District 609 Nanjing, Jiangsu 210012 610 China 612 Email: sunseawq@huawei.com