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Uijterwaal 3 Internet-Draft RIPE NCC 4 Intended status: Standards Track October 7, 2008 5 Expires: April 10, 2009 7 A One-Way Packet Duplication Metric 8 draft-ietf-ippm-duplicate-05.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 April 10, 2009. 35 Abstract 37 When a packet is sent from one host to the other, one normally 38 expects that exactly one copy of the packet that was sent arrives at 39 the destination. It is, however, possible that a packet is either 40 lost or that multiple copies arrive. 42 In earlier work a metric for packet loss has been defined. This 43 metric quantifies the case where a packet that is sent, does not 44 arrive at its destination within a reasonable time. In this memo, a 45 metric for another case is defined: a packet is sent, but multiple 46 copies arrive. The document also discusses streams and methods to 47 summarize the results of streams. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 52 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 4 53 1.2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4 54 2. A Singleton Definition for one-way packet arrival count . . . 5 55 2.1. Metric Name . . . . . . . . . . . . . . . . . . . . . . . 5 56 2.2. Metrics Parameters . . . . . . . . . . . . . . . . . . . . 5 57 2.3. Metric Units . . . . . . . . . . . . . . . . . . . . . . . 5 58 2.4. Definition . . . . . . . . . . . . . . . . . . . . . . . . 5 59 2.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . 6 60 2.6. Methodology . . . . . . . . . . . . . . . . . . . . . . . 6 61 2.7. Errors and uncertainties . . . . . . . . . . . . . . . . . 7 62 2.8. Reporting the metric . . . . . . . . . . . . . . . . . . . 7 63 3. A Singleton Definition for one-way packet duplication . . . . 7 64 3.1. Metric Name . . . . . . . . . . . . . . . . . . . . . . . 7 65 3.2. Metrics Parameters . . . . . . . . . . . . . . . . . . . . 7 66 3.3. Metric Units . . . . . . . . . . . . . . . . . . . . . . . 7 67 3.4. Definition . . . . . . . . . . . . . . . . . . . . . . . . 7 68 3.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . 8 69 4. Definition for samples for one-way Packet Duplication . . . . 8 70 4.1. Poisson Streams . . . . . . . . . . . . . . . . . . . . . 8 71 4.1.1. Metric Name . . . . . . . . . . . . . . . . . . . . . 8 72 4.1.2. Metric Parameters . . . . . . . . . . . . . . . . . . 8 73 4.1.3. Metric Units . . . . . . . . . . . . . . . . . . . . . 8 74 4.1.4. Definition . . . . . . . . . . . . . . . . . . . . . . 8 75 4.1.5. Methodology . . . . . . . . . . . . . . . . . . . . . 9 76 4.1.6. Errors and uncertainties . . . . . . . . . . . . . . . 9 77 4.1.7. Reporting the metric . . . . . . . . . . . . . . . . . 9 78 4.2. Periodic Streams . . . . . . . . . . . . . . . . . . . . . 9 79 4.2.1. Metric Name . . . . . . . . . . . . . . . . . . . . . 9 80 4.2.2. Metric Parameters . . . . . . . . . . . . . . . . . . 9 81 4.2.3. Metric Units . . . . . . . . . . . . . . . . . . . . . 9 82 4.2.4. Definition . . . . . . . . . . . . . . . . . . . . . . 9 83 4.2.5. Methodology . . . . . . . . . . . . . . . . . . . . . 9 84 4.2.6. Errors and uncertainties . . . . . . . . . . . . . . . 10 85 4.2.7. Reporting the metric . . . . . . . . . . . . . . . . . 10 86 5. Some statistics definitions for one-way Duplication . . . . . 10 87 5.1. Type-P-one-way-packet-duplication-fraction . . . . . . . . 10 88 5.2. Type-P-one-way-replicated-packet-rate . . . . . . . . . . 10 89 5.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 11 90 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 91 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 92 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 93 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 94 9.1. Normative References . . . . . . . . . . . . . . . . . . . 13 95 9.2. Informative References . . . . . . . . . . . . . . . . . . 13 96 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13 97 Intellectual Property and Copyright Statements . . . . . . . . . . 14 99 1. Introduction 101 This document defines a metric for one-way packet duplication across 102 Internet paths. It builds on the IPPM Framework document [RFC2330]; 103 the reader is assumed to be familiar with that document. 105 This document follows the same structure as the document for one-way 106 Packet Loss [RFC2680]; the reader is assumed to be familiar with that 107 document as well. 109 The structure of this memo is as follows: 110 o First, a singleton metric, called Type-P-one-way-packet-arrival- 111 count, is introduced to measure the number of arriving packets for 112 each packet sent. 113 o Then, a singleton metric, called Type-P-one-way-packet- 114 duplication, is defined to describe a single instance of packet 115 duplication. 116 o Next, this singleton metric is used to define samples, Type-P-one- 117 way-Packet-Duplication-Poisson-Stream and Type-P-one-way-Packet- 118 Duplication-Periodic-Stream. These are introduced to measure 119 duplication in a series of packets sent with either Poisson- 120 distributed [RFC2680] or periodic [RFC3432] intervals between the 121 packets. 122 o Finally, statistics that summarize the properties of these samples 123 are introduced. 125 1.1. Requirements notation 127 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 128 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 129 document are to be interpreted as described in [RFC2119]. 131 Although RFC 2119 was written with protocols in mind, the key words 132 are used in this document for similar reasons. They are used to 133 ensure the results of measurements from two different implementations 134 are comparable, and to note instances when an implementation could 135 perturb the network. 137 1.2. Motivation 139 When a packet is sent from one host to the other, one normally 140 expects that exactly one copy of the packet that was sent arrives at 141 the destination. It is, however, possible that a packet is either 142 lost or that multiple copies arrive. 144 In earlier work a metric for packet loss has been defined [RFC2680]. 145 This metric distinguishes between cases where the packet arrives and 146 where the packet does not arrive within a reasonable time. In this 147 memo, a metric for a third outcome is defined: a single packet is 148 sent but multiple copies arrive. 150 As this document describes a case similar to the one discussed in 151 [RFC2680], all considerations from that document on timing and 152 accuracy apply. 154 2. A Singleton Definition for one-way packet arrival count 156 2.1. Metric Name 158 Type-P-one-way-packet-arrival-count 160 2.2. Metrics Parameters 162 o Src, the IP address of a host 163 o Dst, the IP address of a host 164 o T, the wire time of a packet at the source 165 o T0, the maximum waiting time for a packet to arrive at the 166 destination. 168 2.3. Metric Units 170 An integer number 172 2.4. Definition 174 Two packets are considered identical if and only if: 176 o Both contain identical information fields. The recipient thus 177 could take either packet and use the data in an application. The 178 other packet does not contain any additional information. 179 o Both packets appear to have been sent by one and the same host, to 180 one and the same destination. Host are identified by their IP 181 addresses. 182 o Both contain valid, but not necessarily identical IP header 183 fields. 185 The recipient thus could take either packet and use it in an 186 application, the other copy does not contain any additional 187 information. 189 The value of a Type-P-one-way-packet-arrival-count is a positive 190 integer number indicating the number of (uncorrupted and identical) 191 copies received by dst in the interval [T, T+T0] for a packet sent by 192 src at time T. 194 If a packet is sent, but it is lost or does not arrive in the 195 interval [T, T+T0], then the metric is undefined. Applications MAY 196 report an "impossible" value (for example, -1) to indicate this 197 condition instead of undefined. 199 If a packet is fragmented during transport and if, for whatever 200 reason, re-assembly does not occur, then the packet will be deemed 201 lost. It is thus not included in the Type-P-one-way-packet-arrival- 202 count. 204 2.5. Discussion 206 This metric counts the number of packets arriving for each packet 207 sent. The time-out value T0 SHOULD be set to a value when the 208 application could potentially still use the packet and would not 209 discard it automatically. 211 The IP headers do not necessarily have to be identical. This can 212 happen, for example, if two packets take a different route resulting 213 in a different TTL. 215 If this metrics is used in parallel with the Packet Loss Metric 216 [RFC2680], the value of T0 should be the same for both cases in order 217 to keep the results comparable. 219 The metric only counts packets that are not corrupted during 220 transmission and may have been resent automatically by lower layers 221 or intermediate devices. Packets that were corrupted during 222 transmission but nevertheless still arrived at dst are not counted. 224 Clocks do have to be synchronized between src and dst such that it is 225 possible to uniquely and accurately determine the interval [T, T+T0] 226 at both sides. 228 If this metric is used in an active measurement system, the system 229 MUST NOT send multiple packets with identical information fields, in 230 order to avoid that all packets will be declared duplicates. This 231 metric can be used inside a passive measurement system as well, using 232 packets generated by another source. However, if the source can send 233 two identical packets within the interval [T, T+T0], this will be 234 incorrectly labelled as a duplicate, resulting in a false positive. 235 It is up to the implementor to estimate if this scenario is likely to 236 happen and the rate of false positives is acceptable. 238 2.6. Methodology 240 The basic technique to measure this metrics follows the methodology 241 described in [RFC2680], section 2.6, with one exception. 243 [RFC2680] does not specify that the receiving host should be able to 244 receive multiple copies of a single packet, as it only needs one copy 245 to determine the metrics. Implementations for this metric should 246 obviously be capable to receive multiple copies. 248 2.7. Errors and uncertainties 250 Refer to section 2.7 of [RFC2680] 252 2.8. Reporting the metric 254 Refer to section 2.8 of [RFC2680] 256 3. A Singleton Definition for one-way packet duplication 258 3.1. Metric Name 260 Type-P-one-way-packet-duplication 262 3.2. Metrics Parameters 264 o Src, the IP address of a host 265 o Dst, the IP address of a host 266 o T, the wire time of a packet at the source 267 o T0, the maximum waiting time for a packet to arrive at the 268 destination. 270 3.3. Metric Units 272 An integer number. 274 3.4. Definition 276 The value of a Type-P-one-way-packet-duplication is a positive 277 integer number indicating the number of (uncorrupted and identical) 278 additional copies of an individual packet received by dst in the 279 interval [T, T+T0] sent by src at time T. 281 If a packet is sent and only one copy arrives in the interval [T, 282 T+T0], then the metric is 0. If no copy arrives in this interval, 283 then the metric is undefined. Applications MAY report an 284 "impossible" value (for example, -1) to indicate this condition. 286 3.5. Discussion 288 This metric is equal to 290 Type-P-one-way-packet-arrival-count - 1 292 This metric is expected to be used for applications that need to know 293 duplication for an individual packet. All considerations regarding 294 methodology, errors and reporting from the previous section apply. 296 4. Definition for samples for one-way Packet Duplication 298 4.1. Poisson Streams 300 4.1.1. Metric Name 302 Type-P-one-way-Packet-Duplication-Poisson-Stream 304 4.1.2. Metric Parameters 306 o Src, the IP address of a host 307 o Dst, the IP address of a host 308 o Ts, a time 309 o Tf, a time. Ts and Tf specify the time interval when packets can 310 be sent for this stream. 311 o T0, the maximum waiting time for a packet to arrive at the 312 destination. 313 o lambda, a rate in reciprocal seconds 315 4.1.3. Metric Units 317 A sequence of pairs; the elements of each pair are: 318 o T, a time 319 o Type-P-one-way-packet-arrival-count for the packet sent at T. 321 4.1.4. Definition 323 Given Ts, Tf and lambda, we compute a pseudo-random Poisson process 324 beginning at or before Ts, with average rate lambda and ending at or 325 after Tf. Those time values greater than or equal to Ts, and less 326 than or equal to Tf are then selected. At each of the times in this 327 process, we obtain the value of Type-P-one-way-packet-arrival-count. 328 The value of the sample is the sequence made up of the resulting 329 {time, duplication} pairs. If there are no such pairs, the sequence 330 is of length zero and the sample is said to be empty. 332 4.1.5. Methodology 334 Refer to [RFC2680], section 3.6. 336 4.1.6. Errors and uncertainties 338 Refer to [RFC2680], section 3.7. 340 4.1.7. Reporting the metric 342 Refer to [RFC2680], section 3.8. 344 4.2. Periodic Streams 346 4.2.1. Metric Name 348 Type-P-one-way-Packet-Duplication-Periodic-Stream 350 4.2.2. Metric Parameters 352 o Src, the IP address of a host 353 o Dst, the IP address of a host 354 o Ts, a time 355 o Tf, a time. Ts and Tf specify the time interval when packets can 356 be sent for this stream. 357 o T0, the maximum waiting time for a packet to arrive at the 358 destination. 359 o lambda, a rate in reciprocal seconds 361 4.2.3. Metric Units 363 A sequence of pairs; the elements of each pair are: 364 o T, a time 365 o Type-P-one-way-packet-arrival-count for the packet sent at T. 367 4.2.4. Definition 369 At time Ts, we start sending packets with a constant rate lambda, 370 until time Tf. For each packet sent, we obtain the value of Type-P- 371 one-way-packet-arrival-count. The value of the sample is the 372 sequence made up of the resulting {time, duplication} pairs. If 373 there are no such pairs, the sequence is of length zero and the 374 sample is said to be empty. 376 4.2.5. Methodology 378 Refer to [RFC2680], section 4.5. 380 4.2.6. Errors and uncertainties 382 Refer to [RFC2680], section 4.6. 384 4.2.7. Reporting the metric 386 Refer to [RFC2680], section 4.7. 388 5. Some statistics definitions for one-way Duplication 390 Note: the statistics described in this section can be used for both 391 Type-P-one-way-Packet-Duplication-Poisson-Stream and Type-P-one-way- 392 Packet-Duplication-Periodic-Stream. The application SHOULD report 393 which sample was used as input. 395 5.1. Type-P-one-way-packet-duplication-fraction 397 This statistic gives the fraction of additional packets that arrived 398 in a stream. 400 Given a Type-P-one-way-Packet-Duplication-Poisson-Stream, one first 401 removes all values of Type-P-one-way-Packet-Duplication which are 402 undefined. For the remaining pairs in the stream, one calculates: 403 (Sum Type-P-one-Way-packet-arrival-count/Number of pairs left) - 1 404 (In other words, (number of packets received)/(number of packets sent 405 and not lost).) 407 The number can be expressed as a percentage. 409 Note: this statistic is the equivalent of the Y.1540 IPDR [Y1540] 411 5.2. Type-P-one-way-replicated-packet-rate 413 This statistic gives the fraction of packets that was duplicated (one 414 or more times) in a stream. 416 Given a Type-P-one-way-Packet-Duplication-Poisson-Stream, one first 417 removes all values of Type-P-one-way-packet-arrival-count which are 418 undefined. For the remaining pairs in the stream, one counts the 419 number of pairs with Type-P-one-Way-packet-arrival-count greater than 420 1. Then one calculates the fraction of packets that meet this 421 criterion as a fraction of the total. (In other words: (number of 422 duplicated packets)/(number of packets sent and not lost).). 424 The number can be expressed as a percentage. 426 Note: this statistic is the equivalent of the Y.1540 RIPR [Y1540] 428 5.3. Examples 430 Consider a stream of 4 packets, sent as: 432 (1, 2, 3, 4) 434 and arriving as: 435 o Case 1: (1, 2, 3, 4) 436 o Case 2: (1, 1, 2, 2, 3, 3, 4, 4) 437 o Case 3: (1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4) 438 o Case 4: (1, 1, 1, 2, 3, 3, 3, 4) 440 Case 1: No packets are duplicated in a stream and both the Type-P- 441 one-way-packet-duplication-fraction and the type-P-one-way-packet- 442 replicated-packet-rate are 0. 444 Case 2: Every packet is duplicated once and the Type-P-one-way- 445 packet-duplication-fraction is 100%. The type-P-one-way-replicated- 446 packet-rate is 100% too. 448 Case 3: Every packet is duplicated twice, so the Type-P-one-way- 449 packet-duplication-fraction is 200%. The type-P-one-way-replicated- 450 packet-rate is still 100%. 452 Case 4: Half the packets are duplicated twice and the other half are 453 not duplicated. The Type-P-one-way-packet-duplication-fraction is 454 again 100% and this number does not show the difference with case 2. 455 However, the type-P-one-way-packet-replicated-packet-rate is 50% in 456 this case and 100% in case 2. 458 However, the type-P-one-way-packet-duplication-rate will not show the 459 difference between case 2 and 3. For this, one has to look at the 460 Type-P-one-way-packet-duplication-fraction. 462 Finally, note that the order in which the packets arrived, do not 463 affect the results. For example, these variations of case 2: 464 o Case 2a: (1, 1, 2, 2, 3, 3, 4, 4) 465 o Case 2b: (1, 2, 3, 4, 1, 2, 3, 4) 466 o Case 2c: (1, 2, 3, 4, 4, 3, 2, 1) 467 (as well as any other permutation) all yield the same results for 468 Type-P-one-way-packet-duplication-fraction and the type-P-one-way- 469 replicated-packet-rate. 471 6. Security Considerations 473 Conducting Internet measurements raises both security and privacy 474 concerns. This memo does not specify an implementation of the 475 metrics, so it does not directly affect the security of the Internet 476 nor of applications which run on the Internet. However, 477 implementations of these metrics must be mindful of security and 478 privacy concerns. 480 There are two types of security concerns: potential harm caused by 481 the measurements, and potential harm to the measurements. The 482 measurements could cause harm because they are active, and inject 483 packets into the network. The measurement parameters MUST be 484 carefully selected so that the measurements inject trivial amounts of 485 additional traffic into the networks they measure. If they inject 486 "too much" traffic, they can skew the results of the measurement, and 487 in extreme cases cause congestion and denial of service. 489 The measurements themselves could be harmed by routers giving 490 measurement traffic a different priority than "normal" traffic, or by 491 an attacker injecting artificial measurement traffic. If routers can 492 recognize measurement traffic and treat it separately, the 493 measurements will not reflect actual user traffic. If an attacker 494 injects artificial traffic that is accepted as legitimate, the loss 495 rate will be artificially lowered. Therefore, the measurement 496 methodologies SHOULD include appropriate techniques to reduce the 497 probability measurement traffic can be distinguished from "normal" 498 traffic. Authentication techniques, such as digital signatures, may 499 be used where appropriate to guard against injected traffic attacks. 501 The privacy concerns of network measurement are limited by the active 502 measurements described in this memo. Unlike passive measurements, 503 there can be no release of existing user data. 505 7. IANA Considerations 507 IANA is asked to add this metrics to the IANA IP Performance Metrics 508 (IPPM) Metrics Registry, see [RFC4148]. This section can be removed 509 after this has been done and upon publication as a RFC. 511 8. Acknowledgements 513 The idea to write this draft came up in a meeting with Al Morton, 514 Stanislav Shalunov, Emile Stephan and the author, on the IPPM 515 reporting draft. 517 This document relies heavily on [RFC2680] and the author likes to 518 thank the authors of that document for writing it. 520 Finally, thanks are due to Lars Eggert, Al Morton, Martin Swany and 521 Matt Zekauskas for their comments. 523 9. References 525 9.1. Normative References 527 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 528 Requirement Levels", BCP 14, RFC 2119, March 1997. 530 [RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way 531 Packet Loss Metric for IPPM", RFC 2680, September 1999. 533 9.2. Informative References 535 [RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, 536 "Framework for IP Performance Metrics", RFC 2330, 537 May 1998. 539 [RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network 540 performance measurement with periodic streams", RFC 3432, 541 November 2002. 543 [RFC4148] Stephan, E., "IP Performance Metrics (IPPM) Metrics 544 Registry", BCP 108, RFC 4148, August 2005. 546 [Y1540] "Y.1540 ITU-T Recommendation Y.1540 (2007), Internet 547 protocol data communication service IP packet transfer 548 and availability performance parameters.", 2007. 550 Author's Address 552 Henk Uijterwaal 553 RIPE NCC 554 Singel 258 555 1016 AB Amsterdam 556 The Netherlands 558 Phone: +31 20 535 4444 559 Email: henk@ripe.net 561 Full Copyright Statement 563 Copyright (C) The IETF Trust (2008). 565 This document is subject to the rights, licenses and restrictions 566 contained in BCP 78, and except as set forth therein, the authors 567 retain all their rights. 569 This document and the information contained herein are provided on an 570 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 571 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 572 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 573 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 574 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 575 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 577 Intellectual Property 579 The IETF takes no position regarding the validity or scope of any 580 Intellectual Property Rights or other rights that might be claimed to 581 pertain to the implementation or use of the technology described in 582 this document or the extent to which any license under such rights 583 might or might not be available; nor does it represent that it has 584 made any independent effort to identify any such rights. 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