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Uijterwaal 3 Internet-Draft RIPE NCC 4 Intended status: Standards Track February 11, 2008 5 Expires: August 14, 2008 7 A One-Way Packet Duplication Metric 8 draft-ietf-ippm-duplicate-03.txt 10 Status of this Memo 12 By submitting this Internet-Draft, each author represents that any 13 applicable patent or other IPR claims of which he or she is aware 14 have been or will be disclosed, and any of which he or she becomes 15 aware will be disclosed, in accordance with Section 6 of BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 This Internet-Draft will expire on August 14, 2008. 35 Copyright Notice 37 Copyright (C) The IETF Trust (2008). 39 Abstract 41 When a packet is sent from one host to the other, one normally 42 expects that exactly one copy of the packet that was sent arrives at 43 the destination. It is, however, possible that a packet is either 44 lost or that multiple copies arrive. 46 In earlier work, the IPPM (IP Performance Metrics) group defined a 47 metric for packet loss. This metric quantifies the case where a 48 packet that is sent, never arrives at its destination. In this memo, 49 a metric for the opposite case is defined: a packet is sent, but 50 multiple copies arrive. The document also discusses streams and 51 methods to summarize the results of streams. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 4 57 1.2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4 58 2. A Singleton Definition for one-way packet arrival count . . . 5 59 2.1. Metric Name . . . . . . . . . . . . . . . . . . . . . . . 5 60 2.2. Metrics Parameters . . . . . . . . . . . . . . . . . . . . 5 61 2.3. Metric Units . . . . . . . . . . . . . . . . . . . . . . . 5 62 2.4. Definition . . . . . . . . . . . . . . . . . . . . . . . . 5 63 2.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . 5 64 2.6. Methodology . . . . . . . . . . . . . . . . . . . . . . . 6 65 2.7. Errors and uncertainties . . . . . . . . . . . . . . . . . 6 66 2.8. Reporting the metric . . . . . . . . . . . . . . . . . . . 6 67 3. A Singleton Definition for one-way packet duplication . . . . 6 68 3.1. Metric Name . . . . . . . . . . . . . . . . . . . . . . . 6 69 3.2. Metrics Parameters . . . . . . . . . . . . . . . . . . . . 7 70 3.3. Metric Units . . . . . . . . . . . . . . . . . . . . . . . 7 71 3.4. Definition . . . . . . . . . . . . . . . . . . . . . . . . 7 72 3.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . 7 73 4. Definition for samples for one-way Packet Duplication . . . . 7 74 4.1. Poisson Streams . . . . . . . . . . . . . . . . . . . . . 7 75 4.1.1. Metric Name . . . . . . . . . . . . . . . . . . . . . 7 76 4.1.2. Metric Parameters . . . . . . . . . . . . . . . . . . 7 77 4.1.3. Metric Units . . . . . . . . . . . . . . . . . . . . . 8 78 4.1.4. Definition . . . . . . . . . . . . . . . . . . . . . . 8 79 4.1.5. Methodology . . . . . . . . . . . . . . . . . . . . . 8 80 4.1.6. Errors and uncertainties . . . . . . . . . . . . . . . 8 81 4.1.7. Reporting the metric . . . . . . . . . . . . . . . . . 8 82 4.2. Periodic Streams . . . . . . . . . . . . . . . . . . . . . 8 83 4.2.1. Metric Name . . . . . . . . . . . . . . . . . . . . . 8 84 4.2.2. Metric Parameters . . . . . . . . . . . . . . . . . . 8 85 4.2.3. Metric Units . . . . . . . . . . . . . . . . . . . . . 9 86 4.2.4. Definition . . . . . . . . . . . . . . . . . . . . . . 9 87 4.2.5. Methodology . . . . . . . . . . . . . . . . . . . . . 9 88 4.2.6. Errors and uncertainties . . . . . . . . . . . . . . . 9 89 4.2.7. Reporting the metric . . . . . . . . . . . . . . . . . 9 90 5. Some statistics definitions for one-way Duplication . . . . . 9 91 5.1. Type-P-one-way-packet-duplication-fraction . . . . . . . . 9 92 5.2. Type-P-one-way-replicated-packet-rate . . . . . . . . . . 10 93 5.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 10 94 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 95 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 96 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 97 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 98 9.1. Normative References . . . . . . . . . . . . . . . . . . . 12 99 9.2. Informative References . . . . . . . . . . . . . . . . . . 12 100 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13 101 Intellectual Property and Copyright Statements . . . . . . . . . . 14 103 1. Introduction 105 This document defines a metric for one-way packet duplication across 106 Internet paths. It builds on the IPPM Framework document [RFC2330]; 107 the reader is assumed to be familiar with that document. 109 This document follows the same structure as the document for one-way 110 Packet Loss [RFC2680]; the reader is assumed to be familiar with that 111 document as well. 113 The structure of this memo is as follows: 114 o First, a singleton metric, called Type-P-one-way-packet-arrival- 115 count, is introduced to measure the number of arriving packets for 116 each packet sent. 117 o Then, a singleton metric, called Type-P-one-way-packet- 118 duplication, is defined to describe a single instance of packet 119 duplication. 120 o Next, this singleton metric is used to define samples, Type-P-one- 121 way-Packet-Duplication-Poisson-Stream and Type-P-one-way-Packet- 122 Duplication-Periodic-Stream. These are introduced to measure 123 duplication in a series of packets sent with either Poisson- 124 distributed [RFC2680] or periodic [RFC3432] intervals between the 125 packets. 126 o Finally, a method to summarise the properties of these samples are 127 introduced. 129 1.1. Requirements notation 131 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 132 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 133 document are to be interpreted as described in [RFC2119]. 135 1.2. Motivation 137 When a packet is sent from one host to the other, one normally 138 expects that exactly one copy of the packet that was sent arrives at 139 the destination. It is, however, possible that a packet is either 140 lost or that multiple copies arrive. 142 In earlier work, the IPPM (IP Performance Metrics) group defined a 143 metric for packet loss [RFC2680]. This metric quantifies the case 144 where a packet that is sent, never arrives at its destination. In 145 this memo, a metric for the opposite case is defined: a packet is 146 sent, but multiple copies arrive. 148 As this document describes a case similar to the one discussed in 149 [RFC2680], all considerations from that document on timing and 150 accuracy apply. 152 2. A Singleton Definition for one-way packet arrival count 154 2.1. Metric Name 156 Type-P-one-way-packet-arrival-count 158 2.2. Metrics Parameters 160 o Src, the IP address of a host 161 o Dst, the IP address of a host 162 o T, a time 163 o T0, a time 165 2.3. Metric Units 167 An integer number 169 2.4. Definition 171 Two packets are considered identical when were sent by one and the 172 same host and contain identical information fields. The recipient 173 thus could take either packet and use it in an application, the other 174 copy would not contain any additional information. 176 The IP headers do not necessarily have to be identical. 178 The value of a Type-P-one-way-packet-arrival-count is a positive 179 integer number indicating the number of (uncorrupted and identical) 180 copies received by dst in the interval [T, T+T0] for a packet sent by 181 src at time T. 183 If a packet is sent, but it is lost or does not arrive in the 184 interval [T, T+T0], then the metric is undefined. Applications MAY 185 report an "impossible" value (for example, -1) to indicate this 186 condition instead of undefined. 188 If a packet is fragmented during transport and if, for whatever 189 reason, re-assembly does not occur, then the packet will be deemed 190 lost. It is thus not included in the Type-P-one-way-packet-arrival- 191 count. 193 2.5. Discussion 195 This metric counts the number of packets arriving for each packet 196 sent. The time-out value T0 SHOULD be set to a value when the 197 application could potentially still use the packet and would not 198 discard it automatically. 200 The IP headers do not necessarily have to be identical. This can 201 happen, for example, if two packets take a different route resulting 202 in a different TTL. 204 If this metrics is used in parallel with the Packet Loss Metric 205 [RFC2680], the value of T0 should be the same for both cases in order 206 to keep the results comparable. 208 The metric only counts packets that are not corrupted during 209 transmission and may have been resent automatically by lower layers 210 or intermediate devices. Packets that were corrupted during 211 transmission but nevertheless still arrived at dst are not counted. 213 Because of the definition of duplication (identical information 214 fields), active measurement systems MUST NOT send multiple packets 215 with identical information fields, in order to avoid that all packets 216 will be declared duplicates. 218 Clocks do have to be synchronized between src and dst in order to be 219 able to uniquely determine the interval [T, T+T0] at both sides. 221 2.6. Methodology 223 The basic technique to measure this metrics follows the methodology 224 described in [RFC2680], section 2.6, with one exception. 226 [RFC2680] does not specify that the receiving host should be able to 227 receive multiple copies of a single packet, as it only needs one copy 228 to determine the metrics. Implementations for this metric should 229 obviously be capable to receive multiple copies. 231 2.7. Errors and uncertainties 233 Refer to section 2.7 of [RFC2680] 235 2.8. Reporting the metric 237 Refer to section 2.8 of [RFC2680] 239 3. A Singleton Definition for one-way packet duplication 241 3.1. Metric Name 243 Type-P-one-way-packet-duplication 245 3.2. Metrics Parameters 247 o Src, the IP address of a host 248 o Dst, the IP address of a host 249 o T, a time 250 o T0, a time 252 3.3. Metric Units 254 An integer number. 256 3.4. Definition 258 The value of a Type-P-one-way-packet-duplication is a positive 259 integer number indicating the number of (uncorrupted and identical) 260 additional copies of an individual packet received by dst in the 261 interval [T, T+T0] sent by src at time T. 263 If a packet is sent and only one copy arrives in the interval [T, 264 T+T0], then the metric is 0. If no copy arrives in this interval, 265 then the metric is undefined. Applications MAY report an 266 "impossible" value (for example, -1) to indicate this condition. 268 3.5. Discussion 270 This metric is equal to 272 Type-P-one-way-packet-arrival-count - 1 274 This metric is expected to be used for applications that need to know 275 duplication for an individual packet. All considerations regarding 276 methodology, errors and reporting from the previous section apply. 278 4. Definition for samples for one-way Packet Duplication 280 4.1. Poisson Streams 282 4.1.1. Metric Name 284 Type-P-one-way-Packet-Duplication-Poisson-Stream 286 4.1.2. Metric Parameters 288 o Src, the IP address of a host 289 o Dst, the IP address of a host 290 o Ts, a time 291 o T0, a time 292 o Tf, a time 293 o lambda, a rate in reciprocal seconds 295 4.1.3. Metric Units 297 A sequence of pairs; the elements of each pair are: 298 o T, a time 299 o Type-P-one-way-packet-arrival-count for the packet sent at T. 301 4.1.4. Definition 303 Given Ts, Tf and lambda, we compute a pseudo-random Poisson process 304 beginning at or before Ts, with average rate lambda and ending at or 305 after Tf. Those time values greater than or equal to Ts, and less 306 than or equal to Tf are then selected. At each of the times in this 307 process, we obtain the value of Type-P-one-way-packet-arrival-count. 308 The value of the sample is the sequence made up of the resulting 309 {time, duplication} pairs. If there are no such pairs, the sequence 310 is of length zero and the sample is said to be empty. 312 4.1.5. Methodology 314 Refer to [RFC2680], section 3.6. 316 4.1.6. Errors and uncertainties 318 Refer to [RFC2680], section 3.7. 320 4.1.7. Reporting the metric 322 Refer to [RFC2680], section 3.8. 324 4.2. Periodic Streams 326 4.2.1. Metric Name 328 Type-P-one-way-Packet-Duplication-Poisson-Stream 330 4.2.2. Metric Parameters 332 o Src, the IP address of a host 333 o Dst, the IP address of a host 334 o Ts, a time 335 o T0, a time 336 o Tf, a time 337 o lambda, a rate in reciprocal seconds 339 4.2.3. Metric Units 341 A sequence of pairs; the elements of each pair are: 342 o T, a time 343 o Type-P-one-way-packet-arrival-count for the packet sent at T. 345 4.2.4. Definition 347 At time Ts, we start sending packets with a constant rate lambda, 348 until time Tf. For each packet sent, we obtain the value of Type-P- 349 one-way-packet-arrival-count. The value of the sample is the 350 sequence made up of the resulting {time, duplication} pairs. If 351 there are no such pairs, the sequence is of length zero and the 352 sample is said to be empty. 354 4.2.5. Methodology 356 Refer to [RFC2680], section 4.5. 358 4.2.6. Errors and uncertainties 360 Refer to [RFC2680], section 4.6. 362 4.2.7. Reporting the metric 364 Refer to [RFC2680], section 4.7. 366 5. Some statistics definitions for one-way Duplication 368 Note: the statistics described in this section can be used for both 369 Type-P-one-way-Packet-Duplication-Poisson-Stream and Type-P-one-way- 370 Packet-Duplication-Periodic-Stream. The application SHOULD report 371 which sample was used as input. 373 5.1. Type-P-one-way-packet-duplication-fraction 375 This statistics gives the fraction of additional packets that arrived 376 in a stream. 378 Given a Type-P-one-way-Packet-Duplication-Poisson-Stream, one first 379 removes all values of Type-P-one-way-Packet-Duplication which are 380 undefined. For the remaining pairs in the stream, one calculates: 381 (Sum Type-P-one-Way-packet-arrival-count/Number of pairs left) - 1 382 (In other words, #packets received/(#sent and not lost).) 383 The number can be expressed as a percentage. 385 Note: this statistics is the equivalent of the Y.1540 IPDR [Y1540] 387 5.2. Type-P-one-way-replicated-packet-rate 389 This statistics gives the fraction of packets that was duplicated 390 (one or more times) in a stream. 392 Given a Type-P-one-way-Packet-Duplication-Poisson-Stream, one first 393 removes all values of Type-P-one-way-packet-arrival-count which are 394 undefined. For the remaining pairs in the stream, one counts the 395 number of pairs with Type-P-one-Way-packet-arrival-count greater than 396 1. Then one calculates the fraction of packets that meet this 397 criterium as a fraction of the total. (In other words: # with 398 duplication/(#sent and not lost).). 400 The number can be expressed as a percentage. 402 Note: this statistics is the equivalent of the Y.1540 RIPR [Y1540] 404 5.3. Examples 406 Consider a stream of 4 packets, sent as: 408 (1, 2, 3, 4) 410 and arriving as: 411 o Case 1: (1, 2, 3, 4) 412 o Case 2: (1, 1, 2, 2, 3, 3, 4, 4) 413 o Case 3: (1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4) 414 o Case 4: (1, 1, 1, 2, 3, 3, 3, 4) 416 Case 1: No packets are duplicated in a stream and both the Type-P- 417 one-way-packet-duplication-fraction and the type-P-one-way-packet- 418 replicated-packet-rate are 0. 420 Case 2: Every packet is duplicated once and the Type-P-one-way- 421 packet-duplication-fraction is 100%. The type-P-one-way-replicated- 422 packet-rate is 100% too. 424 Case 3: Every packet is duplicated twice, so the Type-P-one-way- 425 packet-duplication-fraction is 200%. The type-P-one-way-replicated- 426 packet-rate is still 100%. 428 Case 4: Half the packets are duplicated twice and the other half are 429 not duplicated. The Type-P-one-way-packet-duplication-fraction is 430 again 100% and this number does not show the difference with case 2. 432 However, the type-P-one-way-packet-replicated-packet-rate is 50% in 433 this case and 100% in case 2. 435 However, the type-P-one-way-packet-duplication-rate will not show the 436 difference between case 2 and 3. For this, one has to look at the 437 Type-P-one-way-packet-duplication-fraction. 439 Finally, note that the order in which the packets arrived, do not 440 affect the results. For example, these variations of case 2: 441 o Case 2a: (1, 1, 2, 2, 3, 3, 4, 4) 442 o Case 2b: (1, 2, 3, 4, 1, 2, 3, 4) 443 o Case 2c: (1, 2, 3, 4, 4, 3, 2, 1) 444 (as well as any other permutation) all yield the same results for 445 Type-P-one-way-packet-duplication-fraction and the type-P-one-way- 446 replicated-packet-rate. 448 6. Security Considerations 450 Conducting Internet measurements raises both security and privacy 451 concerns. This memo does not specify an implementation of the 452 metrics, so it does not directly affect the security of the Internet 453 nor of applications which run on the Internet. However, 454 implementations of these metrics must be mindful of security and 455 privacy concerns. 457 There are two types of security concerns: potential harm caused by 458 the measurements, and potential harm to the measurements. The 459 measurements could cause harm because they are active, and inject 460 packets into the network. The measurement parameters MUST be 461 carefully selected so that the measurements inject trivial amounts of 462 additional traffic into the networks they measure. If they inject 463 "too much" traffic, they can skew the results of the measurement, and 464 in extreme cases cause congestion and denial of service. 466 The measurements themselves could be harmed by routers giving 467 measurement traffic a different priority than "normal" traffic, or by 468 an attacker injecting artificial measurement traffic. If routers can 469 recognize measurement traffic and treat it separately, the 470 measurements will not reflect actual user traffic. If an attacker 471 injects artificial traffic that is accepted as legitimate, the loss 472 rate will be artificially lowered. Therefore, the measurement 473 methodologies SHOULD include appropriate techniques to reduce the 474 probability measurement traffic can be distinguished from "normal" 475 traffic. Authentication techniques, such as digital signatures, may 476 be used where appropriate to guard against injected traffic attacks. 478 The privacy concerns of network measurement are limited by the active 479 measurements described in this memo. Unlike passive measurements, 480 there can be no release of existing user data. 482 7. IANA Considerations 484 IANA is asked to add this metrics to the IANA IP Performance Metrics 485 (IPPM) Metrics Registry, see [RFC4148]. This section can be removed 486 after this has been done and upon publication as a RFC. 488 8. Acknowledgements 490 The idea to write this draft came up in a meeting with Al Morton, 491 Stanislav Shalunov, Emile Stephan and the author, on the IPPM 492 reporting draft. 494 This document relies heavily on [RFC2680] and the author likes to 495 thank the authors of that document for writing it. 497 Finally, thanks are due to Martin Swany and Matt Zekauskas for their 498 comments. 500 9. References 502 9.1. Normative References 504 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 505 Requirement Levels", BCP 14, RFC 2119, March 1997. 507 9.2. Informative References 509 [RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, 510 "Framework for IP Performance Metrics", RFC 2330, 511 May 1998. 513 [RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way 514 Packet Loss Metric for IPPM", RFC 2680, September 1999. 516 [RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network 517 performance measurement with periodic streams", RFC 3432, 518 November 2002. 520 [RFC4148] Stephan, E., "IP Performance Metrics (IPPM) Metrics 521 Registry", BCP 108, RFC 4148, August 2005. 523 [Y1540] A. Morton, "Y.1540", July 2003. 525 Author's Address 527 Henk Uijterwaal 528 RIPE NCC 529 Singel 258 530 1016 AB Amsterdam 531 The Netherlands 533 Phone: +31 20 535 4444 534 Email: henk@ripe.net 536 Full Copyright Statement 538 Copyright (C) The IETF Trust (2008). 540 This document is subject to the rights, licenses and restrictions 541 contained in BCP 78, and except as set forth therein, the authors 542 retain all their rights. 544 This document and the information contained herein are provided on an 545 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 546 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 547 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 548 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 549 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 550 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 552 Intellectual Property 554 The IETF takes no position regarding the validity or scope of any 555 Intellectual Property Rights or other rights that might be claimed to 556 pertain to the implementation or use of the technology described in 557 this document or the extent to which any license under such rights 558 might or might not be available; nor does it represent that it has 559 made any independent effort to identify any such rights. 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