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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references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) == Outdated reference: A later version (-20) exists of draft-ietf-payload-flexible-fec-scheme-01 Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 1 comment (--).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 3 Internet-Draft callstats.io 4 Intended status: Standards Track C. Perkins 5 Expires: June 15, 2016 University of Glasgow 6 A. Clark 7 Telchemy 8 R. Huang 9 Huawei 10 December 13, 2015 12 RTP Control Protocol (RTCP) Extended Report (XR) Block for Independent 13 Reporting of Burst/Gap Discard Metric 14 draft-ietf-xrblock-independent-burst-gap-discard-00 16 Abstract 18 This document defines an RTP Control Protocol (RTCP) Extended Report 19 (XR) block that allows the reporting of burst and gap discard metrics 20 independently of the burst and gap loss metrics for use in a range of 21 RTP applications. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on June 15, 2016. 40 Copyright Notice 42 Copyright (c) 2015 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 1.1. Burst-Gap Discard Metrics Block . . . . . . . . . . . . . 2 59 1.2. RTCP and RTCP Extended Reports . . . . . . . . . . . . . 3 60 1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3 61 1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 4 62 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 63 3. Burst/Gap Discard Metrics Block . . . . . . . . . . . . . . . 5 64 3.1. Report Block Structure . . . . . . . . . . . . . . . . . 5 65 3.2. Definition of Fields in Burst/Gap Discard Metrics Block . 5 66 3.3. Derived Metrics Based on the Reported Metrics . . . . . . 7 67 4. Considerations for Voice-over-IP Applications . . . . . . . . 8 68 5. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 8 69 5.1. SDP rtcp-xr Attribute Extension . . . . . . . . . . . . . 8 70 5.2. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . 9 71 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 72 6.1. New RTCP XR Block Type Value . . . . . . . . . . . . . . 9 73 6.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 9 74 6.3. Contact Information for Registrations . . . . . . . . . . 9 75 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 76 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9 77 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 78 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 79 10.1. Normative References . . . . . . . . . . . . . . . . . . 10 80 10.2. Informative References . . . . . . . . . . . . . . . . . 10 81 Appendix A. Metrics Represented Using the Template from RFC 6390 12 83 1. Introduction 85 1.1. Burst-Gap Discard Metrics Block 87 This document defines a new block type that extends the metrics 88 defined in [RFC7003], the metrics in this report block can be used in 89 a range of RTP applications. The new block type reports the 90 proportion of packets discarded by the jitter buffer at the receiver 91 in a burst and number of packets discarded depends on the de-jitter 92 buffer algorithm implemented by the endpoint. 94 The new report block defined in this document is different from the 95 one defined in [RFC7003]. The metrics in [RFC7003] depends on the 96 metrics in the burst-gap loss metric defined in [RFC6958]. 98 Consequently, an endpoint using [RFC7003] MUST report it along with 99 [RFC6958] for it to be useful. The combined usage is useful when an 100 endpoint observes correlated packet losses and discard. However, 101 when the burst of packet losses and discards do not occur 102 simultaneously, the application may prefer a concise report block 103 that just reports the burst-gap of discarded packets. The report 104 block in this document provides the complete information and does not 105 require additional report blocks. That is, this block reports: the 106 total number of packets discarded, the total burst duration, and the 107 total number of bursts, all of these metrics are missing in 108 [RFC7003]. 110 This block provides information on transient network issues. Burst/ 111 gap metrics are typically used in cumulative reports; however, they 112 may also be used in interval reports (see the Interval Metric flag in 113 Section 3.2). The variation in the number of packet discard in a 114 burst affects the user experience. Based on the metrics reported in 115 the block, the sending endpoint may change the packetisation 116 interval, vary the bitrate, etc. The report may additionally be used 117 for diagnostics [RFC6792]. The metric belongs to the class of 118 transport-related end-system metrics defined in [RFC6792]. 120 The definitions of "burst", "gap", "loss", and "discard" are 121 consistent with the definitions in [RFC3611]. To accommodate the 122 range of jitter buffer algorithms and packet discard logic that may 123 be used by implementors, the method used to distinguish between 124 bursts and gaps shall use an equivalent method to that defined in 125 Section 4.7.2 of [RFC3611]. Note that reporting the specific jitter 126 buffer algorithms and/or packet discard logic is out of the scope of 127 this document. 129 1.2. RTCP and RTCP Extended Reports 131 The use of RTCP for reporting is defined in [RFC3550]. [RFC3611] 132 defined an extensible structure for reporting using an RTCP Extended 133 Report (XR). This document defines a new Extended Report block for 134 use with [RFC3550] and [RFC3611]. 136 1.3. Performance Metrics Framework 138 The Performance Metrics Framework [RFC6390] provides guidance on the 139 definition and specification of performance metrics. The RTP 140 Monitoring Framework [RFC6792] provides guidelines for reporting 141 block format using RTCP XR. The metrics block described in this 142 document is in accordance with the guidelines in [RFC6390] and 143 [RFC6792]. 145 1.4. Applicability 147 These metrics are applicable to a range of RTP applications that 148 contain de-jitter buffers [RFC5481] at the receiving end to smooth 149 variation in packet-arrival time and don't use stream repair means, 150 e.g., Forward Error Correction (FEC) 151 [I-D.ietf-payload-flexible-fec-scheme] and/or retransmission 152 [RFC4588]. 154 2. Terminology 156 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 157 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 158 document are to be interpreted as described in RFC 2119 [RFC2119]. 160 In addition, the following terms are defined: 162 Received, Lost, and Discarded 164 A packet shall be regarded as "lost" if it fails to arrive within 165 an implementation-specific time window. A packet that arrives 166 within this time window but is too early to be played out, too 167 late to be played out, or thrown away before playout due to packet 168 duplication or redundancy shall be regarded as discarded. A 169 packet shall not be regarded as discarded if it arrives within 170 this time window but is dropped during decoding by some higher- 171 layer decoder, e.g., due to a decoding error. A packet shall be 172 classified as one of received (or OK), discarded, or lost. The 173 metric "cumulative number of packets lost" defined in [RFC3550] 174 reports a count of packets lost from the media stream (single 175 synchronization source (SSRC) within a single RTP session). 176 Similarly, the metric "number of packets discarded" defined in 177 [RFC7002] reports a count of packets discarded from the media 178 stream (single SSRC within a single RTP session) arriving at the 179 receiver. Another metric, defined in [RFC5725], is available to 180 report on packets that are not recovered by any repair techniques 181 that may be in use. Note that the term "discard" defined here 182 builds on the "discard" definition in [RFC3611] but extends the 183 concept to take into account packet duplication and reports 184 different types of discard counts [RFC7002]. 186 Bursts and Gaps 188 The terms "burst" and "gap" are used in a manner consistent with 189 that of RTCP XR [RFC3611]. RTCP XR views an RTP stream as being 190 divided into bursts, which are periods during which the discard 191 rate is high enough to cause noticeable quality degradation 192 (generally over 5 percent discard rate), and gaps, which are 193 periods during which discarded packets are infrequent and hence 194 quality is generally acceptable. 196 3. Burst/Gap Discard Metrics Block 198 Metrics in this block report on burst/gap discard in the stream 199 arriving at the RTP system. Measurements of these metrics are made 200 at the receiving end of the RTP stream. Instances of this metrics 201 block use the synchronization source (SSRC) to refer to the separate 202 auxiliary Measurement Information Block [RFC6776], which describes 203 measurement periods in use (see [RFC6776], Section 4.2). 205 This metrics block relies on the measurement period in the 206 Measurement Information Block indicating the span of the report. 207 Senders MUST send this block in the same compound RTCP packet as the 208 Measurement Information Block. Receivers MUST verify that the 209 measurement period is received in the same compound RTCP packet as 210 this metrics block. If not, this metrics block MUST be discarded. 212 3.1. Report Block Structure 214 The structure of the Burst/Gap Discard Metrics Block is as follows. 216 0 1 2 3 217 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 1 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 219 | BT=IBGD | I | resv | block length | 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 221 | SSRC of Source | 222 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 223 | Threshold | Sum of Burst Durations (ms) | 224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 225 | Packets Discarded in Bursts | Number of | 226 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 227 | Bursts | Total Packets Expected in Bursts | 228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 229 | Discard Count | 230 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 232 Figure 1: Report Block Structure 234 3.2. Definition of Fields in Burst/Gap Discard Metrics Block 236 Block Type (BT): 8 bits 238 A Burst/Gap Discard Metrics Block is identified by the constant 239 IBGD. 241 [Note to RFC Editor: Please replace IBGD with the IANA provided 242 RTCP XR block type for this block.] 244 Interval Metric flag (I): 2 bits 246 This field is used to indicate whether the burst/gap discard 247 metrics are Sampled, Interval, or Cumulative metrics [RFC6792]: 249 I=10: Interval Duration - the reported value applies to the 250 most recent measurement interval duration between successive 251 metrics reports. 253 I=11: Cumulative Duration - the reported value applies to the 254 accumulation period characteristic of cumulative measurements. 256 I=01: Sampled Value - the reported value is a sampled 257 instantaneous value. 259 In this document, burst/gap discard metrics can only be measured 260 over definite intervals and cannot be sampled. Also, the value 261 I=00 is reserved for future use. Senders MUST NOT use the values 262 I=00 or I=01. If a block is received with I=00 or I=01, the 263 receiver MUST discard the block. 265 Reserved (resv): 6 bits 267 These bits are reserved. They MUST be set to zero by senders and 268 ignored by receivers (see [RFC6709], Section 4.2). 270 block length: 16 bits 272 The length of this report block in 32-bit words, minus one. For 273 the Burst/Gap Discard Metrics Block, the block length is equal to 274 5. The block MUST be discarded if the block length is set to a 275 different value. 277 SSRC of Source: 32 bits 279 As defined in Section 4.1 of [RFC3611]. 281 Threshold: 8 bits 283 The Threshold is equivalent to Gmin in [RFC3611], i.e., the number 284 of successive packets that must not be discarded prior to and 285 following a discard packet in order for this discarded packet to 286 be regarded as part of a gap. Note that the Threshold is set in 287 accordance with the Gmin calculation defined in Section 4.7.2 of 288 [RFC3611]. 290 Sum of Burst Durations (ms): 24 bits 292 The total duration of bursts of discarded packets in the period of 293 the report (Interval or Cumulative). 295 The measured value is an unsigned value. If the measured value 296 exceeds 0xFFFFFD, the value 0xFFFFFE MUST be reported to indicate 297 an over-range measurement. If the measurement is unavailable, the 298 value 0xFFFFFF MUST be reported. 300 Packets Discarded in Bursts: 24 bits 302 The total number of packets discarded during discard bursts, as 303 defined in Section 3.2 of [RFC7002]. 305 Number of Bursts: 16 bits 307 The number of discard bursts in the period of the report (Interval 308 or Cumulative). 310 The measured value is an unsigned value. If the measured value 311 exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an 312 over-range measurement. If the measurement is unavailable, the 313 value 0xFFFF MUST be reported. 315 Total Packets Expected in Bursts: 24 bits 317 The total number of packets expected during discarded bursts (that 318 is, the sum of received packets and lost packets). The metric is 319 defined in [RFC7003]. 321 Discard Count: 32 bits 323 Number of packets discarded over the period (Interval or 324 Cumulative) covered by this report, as defined in Section 3.2 of 325 [RFC7002]. 327 3.3. Derived Metrics Based on the Reported Metrics 329 The metrics described here are intended to be used in conjunction 330 with information from the Measurement Information Block [RFC6776]. 332 These metrics provide the following information relevant to 333 statistical parameters (depending on cumulative of interval 334 measures), for example: 336 o The average discarded burst size, which can be calculated by 337 dividing the metric "Packets Discarded in Bursts" with the "Number 338 of Bursts". 340 o The average burst duration, which can be calculated by dividing 341 the metric "Sum of Burst Durations (ms)" with the "Number of 342 bursts". 344 4. Considerations for Voice-over-IP Applications 346 This metrics block is applicable to a broad range of RTP 347 applications. Where the metric is used with a Voice-over-IP (VoIP) 348 application and the stream repair means is not available, the 349 following considerations apply. 351 RTCP XR views a call as being divided into bursts, which are periods 352 during which the discard rate is high enough to cause noticeable call 353 quality degradation (generally over 5 percent discard rate) and gaps, 354 which are periods during which discarded packets are infrequent and 355 hence call quality is generally acceptable. 357 If voice activity detection is used, the burst and gap duration shall 358 be determined as if silence packets had been sent, i.e., a period of 359 silence in excess of Gmin packets will terminate a burst condition. 361 The recommended value for the threshold Gmin in [RFC3611] results in 362 a burst being a period of time during which the call quality is 363 degraded to a similar extent to a typical pulse code modulation (PCM) 364 severely errored second. 366 5. SDP Signaling 368 [RFC3611] defines the use of SDP (Session Description Protocol) 369 [RFC4566] for signaling the use of XR blocks. XR blocks MAY be used 370 without prior signaling. 372 5.1. SDP rtcp-xr Attribute Extension 374 This section augments the SDP [RFC4566] attribute "rtcp-xr" defined 375 in [RFC3611] by providing an additional value of "xr-format" to 376 signal the use of the report block defined in this document. The 377 ABNF [RFC5234] syntax is as follows. 379 xr-format =/ xr-ind-bgd-block 381 xr-ind-bgd-block = "ind-burst-gap-discard" 383 5.2. Offer/Answer Usage 385 When SDP is used in Offer/Answer context, the SDP Offer/Answer usage 386 defined in [RFC3611] for unilateral "rtcp-xr" attribute parameters 387 applies. For detailed usage in Offer/Answer for unilateral 388 parameters, refer to Section 5.2 of [RFC3611]. 390 6. IANA Considerations 392 New block types for RTCP XR are subject to IANA registration. For 393 general guidelines on IANA considerations for RTCP XR, refer to 394 [RFC3611]. 396 6.1. New RTCP XR Block Type Value 398 This document assigns the block type value IBGD in the IANA "RTP 399 Control Protocol Extended Reports (RTCP XR) Block Type Registry" to 400 the "Burst/Gap Discard Metrics Block". 402 [Note to RFC Editor: Please replace IBGD with the IANA provided RTCP 403 XR block type for this block.] 405 6.2. New RTCP XR SDP Parameter 407 This document also registers a new parameter "ind-burst-gap-discard" 408 in the "RTP Control Protocol Extended Reports (RTCP XR) Session 409 Description Protocol (SDP) Parameters Registry". 411 6.3. Contact Information for Registrations 413 The contact information for the registrations is: 415 RAI Area Directors 417 7. Security Considerations 419 It is believed that this RTCP XR block introduces no new security 420 considerations beyond those described in [RFC3611]. This block does 421 not provide per-packet statistics, so the risk to confidentiality 422 documented in Section 7, paragraph 3 of [RFC3611] does not apply. 424 8. Contributors 426 Qin Wu, Rachel Huang, and Alan Clark wrote RFC7003, which this 427 document extends. 429 9. Acknowledgments 431 The authors acknowledge the reviews and feedback provided by various 432 people. 434 10. References 436 10.1. Normative References 438 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 439 Requirement Levels", BCP 14, RFC 2119, March 1997. 441 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 442 Jacobson, "RTP: A Transport Protocol for Real-Time 443 Applications", STD 64, RFC 3550, July 2003. 445 [RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control 446 Protocol Extended Reports (RTCP XR)", RFC 3611, November 447 2003. 449 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 450 Description Protocol", RFC 4566, July 2006. 452 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 453 Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/ 454 RFC5234, January 2008, 455 . 457 [RFC5725] Begen, A., Hsu, D., and M. Lague, "Post-Repair Loss RLE 458 Report Block Type for RTP Control Protocol (RTCP) Extended 459 Reports (XRs)", RFC 5725, February 2010. 461 [RFC6776] Clark, A. and Q. Wu, "Measurement Identity and Information 462 Reporting Using a Source Description (SDES) Item and an 463 RTCP Extended Report (XR) Block", RFC 6776, October 2012. 465 10.2. Informative References 467 [I-D.ietf-payload-flexible-fec-scheme] 468 Singh, V., Begen, A., Zanaty, M., and G. Mandyam, "RTP 469 Payload Format for Flexible Forward Error Correction 470 (FEC)", draft-ietf-payload-flexible-fec-scheme-01 (work in 471 progress), October 2015. 473 [RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. 474 Hakenberg, "RTP Retransmission Payload Format", RFC 4588, 475 July 2006. 477 [RFC5481] Morton, A. and B. Claise, "Packet Delay Variation 478 Applicability Statement", RFC 5481, DOI 10.17487/RFC5481, 479 March 2009, . 481 [RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New 482 Performance Metric Development", BCP 170, RFC 6390, 483 October 2011. 485 [RFC6709] Carpenter, B., Aboba, B., Ed., and S. Cheshire, "Design 486 Considerations for Protocol Extensions", RFC 6709, DOI 487 10.17487/RFC6709, September 2012, 488 . 490 [RFC6792] Wu, Q., Ed., Hunt, G., and P. Arden, "Guidelines for Use 491 of the RTP Monitoring Framework", RFC 6792, DOI 10.17487/ 492 RFC6792, November 2012, 493 . 495 [RFC6958] Clark, A., Zhang, S., Zhao, J., and Q. Wu, "RTP Control 496 Protocol (RTCP) Extended Report (XR) Block for Burst/Gap 497 Loss Metric Reporting", RFC 6958, May 2013. 499 [RFC7002] Clark, A., Zorn, G., and Q. Wu, "RTP Control Protocol 500 (RTCP) Extended Report (XR) Block for Discard Count Metric 501 Reporting", RFC 7002, September 2013. 503 [RFC7003] Clark, A., Huang, R., and Q. Wu, "RTP Control Protocol 504 (RTCP) Extended Report (XR) Block for Burst/Gap Discard 505 Metric Reporting", RFC 7003, September 2013. 507 Appendix A. Metrics Represented Using the Template from RFC 6390 509 a. Threshold Metric 511 * Defined in Appenix A.a of [RFC7003]. 513 b. Sum of burst durations (ms) 515 * Metric Name: Sum of Burst Durations with Discarded RTP 516 Packets. 518 * Metric Description: The total duration of bursts of discarded 519 RTP packets in the period of the report. 521 * Method of Measurement or Calculation: See Section 3.1, Sum of 522 Burst Durations definition. 524 * Units of Measurement: See Section 3.1, Sum of Burst Durations 525 definition. 527 * Measurement Point(s) with Potential Measurement Domain: See 528 Section 3, 1st paragraph. 530 * Measurement Timing: See Section 3, 2nd paragraph for 531 measurement timing and Section 3.1 for Interval Metric flag. 533 * Use and Applications: See Section 1.4. 535 * Reporting Model: See RFC 3611. 537 c. Packets Discarded in Bursts Metric 539 * Defined in Appenix A.b of [RFC7003]. 541 d. Number of bursts 543 * Metric Name: Number of discard bursts in RTP. 545 * Metric Description: The total number of bursts with discarded 546 RTP packets in the period of the report. 548 * Method of Measurement or Calculation: See Section 3.1, Number 549 of discard bursts definition. 551 * Units of Measurement: See Section 3.1 for the Number of bursts 552 definition. 554 * Measurement Point(s) with Potential Measurement Domain: See 555 Section 3, 1st paragraph. 557 * Measurement Timing: See Section 3, 2nd paragraph for 558 measurement timing and Section 3.1 for Interval Metric flag. 560 * Use and Applications: See Section 1.4. 562 * Reporting Model: See RFC 3611. 564 e. Total Packets Expected in Bursts Metric 566 * Defined in Appenix A.c of [RFC7003]. 568 f. Discard Count 570 * Defined in Appenix A.a of [RFC7002]. 572 Authors' Addresses 574 Varun Singh 575 Nemu Dialogue Systems Oy 576 Runeberginkatu 4c A 4 577 Helsinki 00100 578 Finland 580 EMail: varun@callstats.io 581 URI: http://www.callstats.io/ 583 Colin Perkins 584 University of Glasgow 585 School of Computing Science 586 Glasgow G12 8QQ 587 United Kingdom 589 EMail: csp@csperkins.org 591 Alan Clark 592 Telchemy Incorporated 593 2905 Premiere Parkway, Suite 280 594 Duluth, GA 30097 595 USA 597 EMail: alan.d.clark@telchemy.com 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