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Clark 5 Intended status: Standards Track Telchemy 6 Expires: November 16, 2009 May 15, 2009 8 RTCP XR Report Block for Packet Delay Variation Metric Reporting 9 draft-ietf-avt-rtcp-xr-pdv-03.txt 11 Status of this Memo 13 This Internet-Draft is submitted to IETF in full conformance with the 14 provisions of BCP 78 and BCP 79. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt. 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 This Internet-Draft will expire on November 16, 2009. 34 Copyright Notice 36 Copyright (c) 2009 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents in effect on the date of 41 publication of this document (http://trustee.ietf.org/license-info). 42 Please review these documents carefully, as they describe your rights 43 and restrictions with respect to this document. 45 Abstract 47 This document defines an RTCP XR Report Block that allows the 48 reporting of Packet Delay Variation metrics for a range of RTP 49 applications. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 1.1. Packet Delay Variation Metrics Block . . . . . . . . . . . 3 55 1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3 56 1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3 57 1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Packet Delay Variation Metrics Block . . . . . . . . . . . . . 4 59 2.1. Report Block Structure . . . . . . . . . . . . . . . . . . 4 60 2.2. Definition of Fields in PDV Metrics Block . . . . . . . . 4 61 2.3. Guidance on use of PDV metrics . . . . . . . . . . . . . . 7 62 2.4. Examples of use . . . . . . . . . . . . . . . . . . . . . 8 63 3. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 9 64 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 65 4.1. New RTCP XR Block Type value . . . . . . . . . . . . . . . 10 66 4.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 10 67 4.3. Contact information for registrations . . . . . . . . . . 10 68 4.4. New registry of PDV types . . . . . . . . . . . . . . . . 10 69 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 70 6. Changes from previous version . . . . . . . . . . . . . . . . 13 71 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 72 7.1. Normative References . . . . . . . . . . . . . . . . . . . 14 73 7.2. Informative References . . . . . . . . . . . . . . . . . . 14 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 76 1. Introduction 78 1.1. Packet Delay Variation Metrics Block 80 This draft defines a new block type to augment those defined in 81 [RFC3611], for use in a range of RTP applications. 83 The new block type provides information on Packet Delay Variation 84 using one of several standard metrics. 86 The metrics belong to the class of transport metrics defined in 87 [MONARCH] (work in progress). 89 Instances of this Metrics Block refer by tag to the separate 90 auxiliary Measurement Identity block [MEASIDENT] which contains 91 information such as the SSRC of the measured stream, and RTP sequence 92 numbers and time intervals indicating the span of the report. 94 1.2. RTCP and RTCP XR Reports 96 The use of RTCP for reporting is defined in [RFC3550]. [RFC3611] 97 defined an extensible structure for reporting using an RTCP Extended 98 Report (XR). This draft defines a new Extended Report block that 99 MUST be used as defined in [RFC3550] and [RFC3611]. 101 1.3. Performance Metrics Framework 103 The Performance Metrics Framework [PMOLFRAME] provides guidance on 104 the definition and specification of performance metrics. Metrics 105 described in this draft either reference external definitions or 106 define metrics generally in accordance with the guidelines in 107 [PMOLFRAME]. 109 1.4. Applicability 111 These metrics are applicable to a range of RTP applications. 113 2. Packet Delay Variation Metrics Block 115 Metrics in this block report on packet delay variation in the stream 116 arriving at the RTP system. 118 2.1. Report Block Structure 120 PDV metrics block 121 0 1 2 3 122 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 123 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 124 | BT=NPDV |I| tag |pdvtyp | block length=3 | 125 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 126 | Pos Threshold/Peak PDV | Pos PDV Percentile | 127 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 128 | Neg Threshold/Peak PDV | Neg PDV Percentile | 129 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 130 | Mean PDV | unused | 131 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 133 Figure 1: Report Block Structure 135 2.2. Definition of Fields in PDV Metrics Block 137 block type (BT): 8 bits 139 A Packet Delay Variation Metrics Report Block is identified by the 140 constant NPDV. 142 [Note to RFC Editor: please replace NPDV with the IANA provided RTCP 143 XR block type for this block.] 145 Interval Metric flag (I): 1 bit 147 This field is used to indicate whether the Packet Delay Variation 148 metrics block is an Interval or a Cumulative report, that is, 149 whether the reported values apply to the most recent measurement 150 interval duration between successive metrics reports (I=1) (the 151 Interval Duration) or to the accumulation period characteristic of 152 cumulative measurements (I=0) (the Cumulative Duration). 153 Numerical values for both these intervals are provided in the 154 Measurement Identifier block referenced by the tag field below. 156 Measurement Identifier association (tag): 3 bits 158 This field is used to identify the Measurement Identifier block 159 [MEASIDENT] which describes this measurement. The relevant 160 Measurement Identifier block has the same tag value as the Packet 161 Delay Variation Metrics block. Note that there may be more than 162 one Measurement Identifier block per RTCP packet. 164 Packet Delay Variation Metric Type (pdvtyp): 4 bits 166 This field is used to identify the Packet Delay Variation Metric 167 Type used in this report block, according to the following code: 169 bits 014-017 170 0: interarrival jitter, Section 6.4.1 of [RFC3550], 171 1: MAPDV2, Clause 6.2.3.2 of [G.1020], 172 2: 2-point PDV, Clause 6.2.4 of [Y.1540] 174 Other values as registered by IANA in new registry "RTCP XR PDV 175 block - PDV type", see Section 4.4. 177 block length: 16 bits 179 The length of this report block in 32-bit words, minus one. For 180 the Packet Delay Variation Metrics block, the block length is 181 equal to 3. 183 Positive Threshold/Peak PDV: 16 bit, S11:4 format 185 The PDV associated with the Positive PDV percentile expressed in 186 milliseconds. The term Positive is associated with packets 187 arriving later than the expected time. 189 If the measured value is more negative than -2047.9375 (the value 190 which would be coded as 0x8001), the value 0x8000 SHOULD be 191 reported to indicate an over-range negative measurement. If the 192 measured value is more positive than +2047.8125 (the value which 193 would be coded as 0x7FFD), the value 0x7FFE SHOULD be reported to 194 indicate an over-range positive measurement. If the measurement 195 is unavailable, the value 0x7FFF SHOULD be reported. 197 Positive PDV Percentile: 16 bit, 8:8 format 199 The percentage of packets on the call for which individual packet 200 delays were less than the Positive Threshold PDV. 202 If the measurement is unavailable, the value 0xFFFF SHOULD be 203 reported. 205 Negative Threshold/Peak PDV: 16 bit, S11:4 format 206 The PDV associated with the Negative PDV percentile expressed in 207 milliseconds. The term Negative is associated with packets 208 arriving earlier than the expected time. 210 If the measured value is more negative than -2047.9375 (the value 211 which would be coded as 0x8001), the value 0x8000 SHOULD be 212 reported to indicate an over-range negative measurement. If the 213 measured value is more positive than +2047.8125 (the value which 214 would be coded as 0x7FFD), the value 0x7FFE SHOULD be reported to 215 indicate an over-range positive measurement. If the measurement 216 is unavailable, the value 0x7FFF SHOULD be reported. 218 Negative PDV Percentile: 16 bit, 8:8 format 220 The percentage of packets on the call for which individual packet 221 delays were more than the Negative Threshold PDV. 223 If the measurement is unavailable, the value 0xFFFF SHOULD be 224 reported. 226 If the PDV Type indicated is 2-point PDV and the Positive and 227 Negative PDV Percentiles are set to 100.0 then the Positive and 228 Negative Threshold/Peak PDV values are the peak values measured 229 during the reporting interval (which may be from the start of the 230 call for cumulative reports). In this case, the difference between 231 the Positive and Negative Threshold/Peak values defines the range of 232 2-point PDV. 234 Mean PDV: (16 bit, S11:4 format) expressed in milliseconds 236 For MAPDV2 this value is generated according to Clause 6.2.3.2 of 237 [G.1020]. For interval reports the MAPDV2 value is reset at the 238 start of the interval. 240 For interarrival jitter, the value reported is the value of J(i) 241 calculated according to [RFC3550] at the time the report is 242 generated. 244 For 2-point PDV, the value reported is the mean of per-packet 245 2-point PDV values. This metric indicates the arrival time of the 246 first media packet of the session with respect to the mean of the 247 arrival times of every packet of the session. A single value of 248 the metric (for a single session) may not be useful by itself, but 249 its average over a number of sessions may be useful in diagnosing 250 media delay at session startup. For example, this might occur if 251 media packets are often delayed behind signalling packets due to 252 head-of-line blocking. 254 If the measured value is more negative than -2047.9375 (the value 255 which would be coded as 0x8001), the value 0x8000 SHOULD be 256 reported to indicate an over-range negative measurement. If the 257 measured value is more positive than +2047.8125 (the value which 258 would be coded as 0x7FFD), the value 0x7FFE SHOULD be reported to 259 indicate an over-range positive measurement. If the measurement 260 is unavailable, the value 0x7FFF SHOULD be reported. 262 unused: 16 bits 264 These bits are unused. They SHOULD be set to zero by the sender 265 and MUST be ignored by the receiver. 267 2.3. Guidance on use of PDV metrics 269 This subsection provides informative guidance on when it might be 270 appropriate to use each of the PDV metric types. 272 Interarrival jitter (Section 6.4.1 of [RFC3550]) allows comparison of 273 results with those from RTP end systems which support only RTCP as 274 defined in [RFC3550]. 276 MAPDV2 (Clause 6.2.3.2 of [G.1020]) compares instantaneous (per- 277 packet) delay variation against a moving average delay variation. 278 This metric could be useful in determining residual impairment when 279 an RTP end system uses an adaptive de-jitter buffer which tracks the 280 average delay variation, provided the MAPDV2 algorithm and the 281 adaptive de-jitter buffer have similar averaging behaviour. 283 2-point PDV (Clause 6.2.4 of [Y.1540]) reports absolute packet delay 284 variation with respect to the time of arrival of the first packet of 285 the connection. In an RTP context, the two "points" are at the 286 sender (the synchronization source which applies RTP timestamps) and 287 at the receiver. The value of this metric for the packet with index 288 j is identical to the quantity D(i,j) defined in Section 6.4.1 of 289 [RFC3550] if the packet index i is set equal to 1, that is, the 290 reference packet for the metric is the first packet of the 291 connection. The metric includes the effect of the frequency offsets 292 of clocks in both the sender and receiver end systems, so it is 293 useful mainly in network where synchronisation is distributed. As 294 well as measuring packet delay variation in such networks, it may be 295 used to ensure that synchronisation is effective, for example where 296 the network carries ISDN data traffic over RTP [RFC4040]. The metric 297 is likely to be useful in networks which use fixed de-jitter 298 buffering, because it may be used to determine the length of the 299 required de-jitter buffer, or to determine if network performance has 300 deteriorated such that existing de-jitter buffers are too small to 301 accommodate the observed delay variation. 303 2.4. Examples of use 305 (a) To report interarrival jitter [RFC3550]: 307 Threshold PDV = FFFF (Undefined); PDV Percentile = FFFF (Undefined); 308 PDV type = 0 (interarrival jitter) 310 causes interarrival jitter to be reported in the Mean PDV field. 312 (b) To report MAPDV2 [G.1020]: 314 Pos Threshold PDV = 50.0; Pos PDV Percentile = 95.3; Neg Threshold 315 PDV = 50.0 (note this implies -50ms); Neg PDV Percentile = 98.4; PDV 316 type = 1 (MAPDV2) 318 causes average MAPDV2 to be reported in the Mean PDV field. 320 Note that implementations may either fix the reported percentile and 321 calculate the associated PDV level OR may fix a threshold PDV level 322 and calculate the associated percentile. From a practical 323 implementation perspective it is simpler to use the second of these 324 approaches (except of course in the extreme case of a 100% 325 percentile). 327 2-point PDV, according to [Y.1540] is the difference in delay between 328 the current packet and the first packet of the stream. If the 329 sending and receiving clocks are not synchronized, this metric 330 includes the effect of relative timing drift. 332 3. SDP Signaling 334 [RFC3611] defines the use of SDP (Session Description Protocol) 335 [RFC4566] for signaling the use of XR blocks. XR blocks MAY be used 336 without prior signaling. 338 This section augments the SDP [RFC4566] attribute "rtcp-xr" defined 339 in [RFC3611] by providing an additional value of "xr-format" to 340 signal the use of the report block defined in this document. 342 rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF 344 (defined in [RFC3611]) 346 xr-format =/ xr-pdv-block 348 xr-pdv-block = "pkt-dly-var" [ "," pdvtype ] [ "," nspec "," pspec ] 350 pdvtype = "pdv=" 0 ; interarrival jitter RFC 3550 351 / 1 ; MAPDV2 ITU-T G.1020 352 / 2 ; 2-point PDV ITU-T Y.1540 353 nspec = "nthr=" fixpoint ; negative threshold PDV (ms) 354 / "npc=" fixpoint ; negative PDV percentile 355 pspec = "pthr=" fixpoint ; positive threshold PDV (ms) 356 / "ppc=" fixpoint ; positive PDV percentile 358 fixpoint = 1*DIGIT "." 1*DIGIT ; fixed point decimal 359 DIGIT = %x30-39 361 When SDP is used in offer-answer, a system sending SDP may request a 362 specific type of PDV measurement. In addition, they may state a 363 specific percentile or threshold value, and expect to receive the 364 corresponding threshold or percentile metric, respectively. The 365 system receiving the SDP SHOULD send the PDV metrics requested, but 366 if the metric is not available, the system receiving the SDP SHOULD 367 send the flag value indicating that the metric is unavailable. 369 4. IANA Considerations 371 New block types for RTCP XR are subject to IANA registration. For 372 general guidelines on IANA considerations for RTCP XR, refer to 373 [RFC3611]. 375 4.1. New RTCP XR Block Type value 377 This document assigns the block type value NPDV in the IANA "RTCP XR 378 Block Type Registry" to the "Packet Delay Variation Metrics Block". 380 [Note to RFC Editor: please replace NPDV with the IANA provided RTCP 381 XR block type for this block.] 383 4.2. New RTCP XR SDP Parameter 385 This document also registers a new parameter "pkt-dly-var" in the 386 "RTCP XR SDP Parameters Registry". 388 4.3. Contact information for registrations 390 The contact information for the registrations is: 392 Geoff Hunt (geoff.hunt@bt.com) 394 Orion 2 PP3, Adastral Park, Martlesham Heath, Ipswich IP5 3RE, United 395 Kingdom 397 4.4. New registry of PDV types 399 This document creates a new registry to be called "RTCP XR PDV block 400 - PDV type" as a sub-registry of the "RTP Control Protocol Extended 401 Reports (RTCP XR) Block Type Registry". Policies for this new 402 registry are as follows: 404 o The information required to support an assignment is an 405 unambiguous definition of the new metric, covering the base 406 measurements and how they are processed to generate the reported 407 metric. This should include the units of measurement, how values 408 of the metric are reported in the three 16-bit fields "Pos 409 Threshold/Peak PDV", "Neg Threshold/Peak PDV" and "Mean PDV" 410 within the report block, and how the metric uses the two 16-bit 411 fields "Pos PDV Percentile" and "Neg PDV Percentile". 413 o The review process for the registry is "Specification Required" as 414 described in Section 4.1 of [RFC5226]. 416 o Entries in the registry are integers. The valid range is 0 to 15 417 corresponding to the 4-bit field "pdvtyp" in the block. Values 418 are to be recorded in decimal. 420 o Initial assignments are as follows: 422 0: interarrival jitter, Section 6.4.1 of [RFC3550], 423 1: MAPDV2, Clause 6.2.3.2 of [G.1020], 424 2: 2-point PDV, Clause 6.2.4 of [Y.1540] 426 5. Security Considerations 428 It is believed that this proposed RTCP XR report block introduces no 429 new security considerations beyond those described in [RFC3611]. 430 This block does not provide per-packet statistics so the risk to 431 confidentiality documented in Section 7, paragraph 3 of [RFC3611] 432 does not apply. 434 6. Changes from previous version 436 Changed BNF for SDP following Christian Groves' and Tom Taylor's 437 comments (4th and 5th May 2009), now aligned with RFC 5234 section 438 3.3 "Incremental Alternatives". 440 Updated references. 442 7. References 444 7.1. Normative References 446 [G.1020] ITU-T, "ITU-T Rec. G.1020, Performance parameter 447 definitions for quality of speech and other voiceband 448 applications utilizing IP networks", July 2006. 450 [MEASIDENT] 451 Hunt, G., "RTCP XR Measurement Identifier Block", 452 ID draft-ietf-avt-rtcp-xr-meas-identity-02, May 2009. 454 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 455 Requirement Levels", RFC 2119, BCP 14, March 1997. 457 [RFC3550] Schulzrinne, H., "RTP: A Transport Protocol for Real-Time 458 Applications", RFC 3550, July 2003. 460 [RFC3611] Friedman, T., "RTP Control Protocol Extended Reports (RTCP 461 XR)", RFC 3611, November 2003. 463 [RFC4040] Kreuter, R., "RTP Payload Format for a 64 kbit/s 464 Transparent Call", RFC 4040, April 2005. 466 [RFC4566] Handley, M., "SDP: Session Description Protocol", 467 RFC 4566, July 2006. 469 [RFC5226] Narten, T., "Guidelines for Writing an IANA Considerations 470 Section in RFCs", RFC 5226, BCP 26, May 2008. 472 [Y.1540] ITU-T, "ITU-T Rec. Y.1540, IP packet transfer and 473 availability performance parameters", November 2007. 475 7.2. Informative References 477 [MONARCH] Hunt, G., "Monitoring Architectures for RTP", 478 ID draft-hunt-avt-monarch-01, August 2008. 480 [PMOLFRAME] 481 Clark, A., "Framework for Performance Metric Development", 482 ID draft-ietf-pmol-metrics-framework-02, March 2009. 484 Authors' Addresses 486 Geoff Hunt 487 BT 488 Orion 2 PP3 489 Adastral Park 490 Martlesham Heath 491 Ipswich, Suffolk IP5 3RE 492 United Kingdom 494 Phone: +44 1473 651704 495 Email: geoff.hunt@bt.com 497 Alan Clark 498 Telchemy Incorporated 499 2905 Premiere Parkway, Suite 280 500 Duluth, GA 30097 501 USA 503 Email: alan.d.clark@telchemy.com