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Morton 3 Internet-Draft AT&T Labs 4 Intended status: Informational February 23, 2015 5 Expires: August 27, 2015 7 Active and Passive Metrics and Methods (and everything in-between) 8 draft-morton-ippm-active-passive-01 10 Abstract 12 This memo provides clear definitions for Active and Passive 13 performance assessment. The construction of Metrics and Methods can 14 be described as Active or Passive. Methods can take on some of the 15 attributes of both, and we refer to these as Hybrid Methods. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at http://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on August 27, 2015. 34 Copyright Notice 36 Copyright (c) 2015 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 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 53 2. Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . 3 54 3. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 3 55 3.1. Performance Metric . . . . . . . . . . . . . . . . . . . 3 56 3.2. Method of Measurement . . . . . . . . . . . . . . . . . . 3 57 3.3. Observation Point . . . . . . . . . . . . . . . . . . . . 3 58 3.4. Active Methods . . . . . . . . . . . . . . . . . . . . . 4 59 3.5. Active Metric . . . . . . . . . . . . . . . . . . . . . . 4 60 3.6. Passive Methods . . . . . . . . . . . . . . . . . . . . . 4 61 3.7. Passive Metric . . . . . . . . . . . . . . . . . . . . . 5 62 3.8. Hybrid Methods and Metrics . . . . . . . . . . . . . . . 5 63 4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 5 64 4.1. Discussion of PDM . . . . . . . . . . . . . . . . . . . . 7 65 4.2. Discussion of "Coloring" Method . . . . . . . . . . . . . 7 66 5. Security considerations . . . . . . . . . . . . . . . . . . . 8 67 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 68 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 69 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 70 8.1. Normative References . . . . . . . . . . . . . . . . . . 8 71 8.2. Informative References . . . . . . . . . . . . . . . . . 9 72 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 74 1. Introduction 76 The adjectives "active" and "passive" have been used for many years 77 to distinguish two different classes of Internet performance 78 assessment. The first Passive and Active Measurement (PAM) 79 Conference was held in 2000, but the earliest proceedings available 80 on-line are from the second PAM conference in 2001 81 [https://www.ripe.net/ripe/meetings/pam-2001]. 83 The notions of "active" and "passive" are well-established. In 84 general: 86 An Active metric or method depends on a dedicated measurement 87 packet stream. 89 A Passive metric or method depends solely on observation of one or 90 more packet streams. The streams only serve measurement when they 91 are observed for that purpose, and are present whether 92 measurements take place or not. 94 As new techniques for assessment emerge it is helpful to have clear 95 definitions of these notions. This memo provides more detailed 96 definitions and discusses means to evaluate new techniques as they 97 emerge. 99 This memo provides definitions for Active and Passive Metrics and 100 Methods based on long usage in the Internet measurement community, 101 and especially the Internet Engineering Task Force. 103 1.1. Requirements Language 105 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 106 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 107 document are to be interpreted as described in RFC 2119 [RFC2119]. 109 2. Purpose and Scope 111 The scope of this memo is to define and describe Active and Passive 112 versions of metrics and methods which are consistent with the long- 113 time usage of these adjectives in the Internet measurement community 114 and especially the Internet Engineering Task Force. 116 Further, this memo's purpose includes describing multiple dimensions 117 in which to evaluate methods as they emerge. 119 3. Terms and Definitions 121 This section defines the key terms of the memo. 123 3.1. Performance Metric 125 The standard definition of a quantity, produced in an assessment of 126 performance and/or reliability of the network, which has an intended 127 utility and is carefully specified to convey the exact meaning of a 128 measured value. (This definition is consistent with that of 129 Performance Metric in RFC 2330 and RFC 6390). 131 3.2. Method of Measurement 133 The procedure or set of operations having the object of determining a 134 Measured Value or Measurement Result. 136 3.3. Observation Point 138 See section 2 of [RFC7011] for this definition (a location in the 139 network where packets can be observed), and related definitions. The 140 comparable term defined in IETF literature on Active measurement is 141 Measurement Point, see section 4.1 of [RFC5835]. Two terms have come 142 into use describing somewhat actions at the identified point in the 143 network path. 145 3.4. Active Methods 147 Active measurement methods have the following attributes: 149 1. Commonly, the packet stream of interest is generated as the basis 150 of measurement. A packet stream may be generated to increase 151 traffic load, but the loading stream itself may not be measured. 153 2. The packets in the stream of interest have fields (or are 154 augmented or modified to include fields) which are dedicated to 155 measurement. Since measurement usually requires determining the 156 corresponding packets at multiple measurement points, a sequence 157 number is the most common information dedicated to measurement. 159 3. The Source and Destination of the packet stream are usually known 160 a' priori. 162 4. Packet stream characteristics are known at the Source at least, 163 and may be communicated to Destination as part of the method. 165 When adding traffic to the network for measurement, Active Methods 166 influence the quantities measured to some degree, and those 167 performing tests should take steps to quantify the effect(s) and/or 168 minimize such effects. 170 3.5. Active Metric 172 An Active Metric incorporates one or more of the aspects of Active 173 Methods in the metric definition. 175 For example, IETF metrics for IP performance (developed according to 176 the [RFC2330] framework) include the Source packet stream 177 characteristics as metric input parameters, and also specify the 178 packet characteristics (Type-P) and Source and Destination IP 179 addresses (with their implications on both stream treatment and 180 interfaces associated with measurement points). 182 3.6. Passive Methods 184 Passive measurement methods are based on observations of undisturbed 185 packet traffic. Some passive methods simply observe and collect 186 information on all packets that pass Observation Point(s), while 187 others filter the packets as a first step and only collect 188 information on packets that match the filter criteria. 190 It is common that passive methods are conducted at one or more 191 Observation Points. Passive methods to assess Performance Metrics 192 often require multiple observation points, e.g., to assess latency of 193 packet transfer across a network path between two Observation Points. 194 In this case, the observed packets must include enough information to 195 determine the corresponding packets at different Observation Points. 197 Communication of the observations (in some form) to a collector is an 198 essential aspect of Passive Methods. In some configurations, the 199 traffic load associated with results export to a collector may 200 influence the network performance. However, the collection of 201 results is not unique to Passive Methods, and the load from 202 management and operations of measurement systems must always be 203 considered for potential effects on the measured values. 205 3.7. Passive Metric 207 Passive Metrics apply to observations of packet traffic (traffic 208 flows in [RFC7011]). 210 Passive performance metrics are assessed independent of the packets 211 or traffic flows, and solely through observation. Some refer to such 212 assessments as "out-of-band". 214 One example of passive performance metrics for IP packet transfer can 215 be found in ITU-T Recommendation Y.1540, where the metrics are 216 defined on the basis of reference events as packet pass reference 217 points, so the metrics are agnostic to the distinction between active 218 and passive when packet correspondence can be derived from the 219 observed stream when required. 221 3.8. Hybrid Methods and Metrics 223 Methods of Measurement which use a combination of Active Methods and 224 Passive Methods, to assess Active Metrics, Passive Metrics, or a new 225 metrics derived from the observations. ITU-T Recommendation Y.1540 226 defines metrics are applicable to the hybrid category, since packet 227 correspondence at different observation/reference points could be 228 derived from "fields which are dedicated to measurement", but 229 otherwise the methods are passive. 231 4. Discussion 233 If we compare the Active and Passive Methods, there are at least two 234 dimensions on which methods can be evaluated. This evaluation space 235 may be useful when a method is a combination of the two alternative 236 methods. 238 The two dimensions (initially chosen) are: 240 1. The degree to which the measured stream effects overall network 241 conditions. There is also the notion of time averages - a 242 measurement stream may have significant effect while it is 243 present, but the stream is only generated 0.1% of the time. On 244 the other hand, observations alone have no effect on network 245 performance. To keep things simple, we consider the stream 246 effect only when it is present. 248 2. The methodological advantages of knowing the source stream 249 characteristics, and having complete control of the stream 250 characteristics. For example, knowing the number of packets in a 251 stream allows more efficient operation of the measurement 252 receiver, and so is an asset for active measurement methods. 253 Passive methods (with no sample filter) have few clues available 254 to anticipate what the protocol first packet observed will use or 255 how many packets will comprise the flow, but once the standard 256 protocol of a flow is known the possibilities narrow (for some 257 compliant flows). 259 There are a few examples we can plot on a two-dimensional space. We 260 can anchor the dimensions with reference point descriptions. 262 Effect of the measured stream on network conditions 263 ^ Max 264 |* Active using max capacity stream 265 | 266 | 267 | 268 | 269 |* Active using stream with load of typical user 270 | 271 | 272 | 273 |* Active using extremely sparse, randomized stream 274 | * PDM Passive 275 | Min * 276 +----------------------------------------------------------------| 277 | | 278 Stream None 279 Characteristics 280 completely 281 known 283 We recognize that method categorization could be based on additional 284 dimensions, but this would require a different graphical approach. 286 For example, "effect of measured stream on network conditions" could 287 easily be further qualified into: 289 1. effect on the performance of the measured stream itself: for 290 example, choosing a packet marking or DSCP resulting in domain 291 treatment as a real-time stream (as opposed to default/best- 292 effort marking. 294 2. effect on unmeasured flows that share the path and/or 295 bottlenecks: for example, an extremely sparse measured stream of 296 minimal size packets typically has little effect on other flows 297 (and itself), while a stream designed to characterize path 298 capacity may effect all other flows passing through the capacity 299 bottleneck (including itself). 301 3. effect on network conditions, resulting in network adaptation: 302 for example, a network monitoring load and congestion conditions 303 might change routing, placing some flows to alternate paths to 304 mitigate the congestion. 306 As suggestions emerge we will examine the possibilities. 308 4.1. Discussion of PDM 310 In [I-D.elkins-ippm-pdm-option], an IPv6 Option Header is described 311 which (when added to the stream at strategic interfaces) supports 312 performance measurements. This method processes a user traffic 313 stream and adds "fields which are dedicated to measurement". Thus: 315 o The method may have a small effect on the measured stream and 316 other streams in the network. 318 o The measured stream has unknown characteristics until it is 319 processed to add the PDM Option header. 321 We conclude that this is a Hybrid method, having at least one 322 characteristic of both active and passive methods. 324 4.2. Discussion of "Coloring" Method 326 Draft [I-D.tempia-opsawg-p3m], proposed to color packets by re- 327 writing a field of the stream at strategic interfaces to support 328 performance measurements. This method processes a user traffic 329 stream and inserts "fields which are dedicated to measurement". 330 Thus: 332 o The method may have a small effect on the measured stream and 333 other streams in the network (smaller than PDM above). 335 o The measured stream has unknown characteristics until it is 336 processed to add the coloring in the header, and the stream could 337 be measured and time-stamped during that process. 339 We note that [I-D.chen-ippm-coloring-based-ipfpm-framework] proposes 340 a method similar to [I-D.tempia-opsawg-p3m], and ippm-list discussion 341 indicates [I-D.chen-ippm-coloring-based-ipfpm-framework] may be 342 covered by the same IPR as [I-D.tempia-opsawg-p3m]. 344 We conclude that this is a Hybrid method, having at least one 345 characteristic of both active and passive methods. 347 5. Security considerations 349 When considering privacy of those involved in measurement or those 350 whose traffic is measured, there is sensitive information 351 communicated and observed at observation and measurement points 352 described above. We refer the reader to the privacy considerations 353 described in the Large Scale Measurement of Broadband Performance 354 (LMAP) Framework [I-D.ietf-lmap-framework], which covers active and 355 passive measurement techniques and supporting material on measurement 356 context. 358 6. IANA Considerations 360 This memo makes no requests for IANA consideration. 362 7. Acknowledgements 364 Thanks to Mike Ackermann for asking the right question, and for 365 several suggestions on terminology. Brian Trammell provided key 366 terms and references for the passive category. Tiziano Ionta 367 reviewed the draft and suggested the classification for the 368 "coloring" method of measurement. Nalini Elkins identified several 369 areas for clarification following her review. Bill Jouris reviewed 370 01 editorially and suggested several improvements. 372 8. References 374 8.1. Normative References 376 [RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, 377 "Framework for IP Performance Metrics", RFC 2330, May 378 1998. 380 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 381 Requirement Levels", BCP 14, RFC 2119, March 1997. 383 [RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network 384 performance measurement with periodic streams", RFC 3432, 385 November 2002. 387 [RFC5835] Morton, A. and S. Van den Berghe, "Framework for Metric 388 Composition", RFC 5835, April 2010. 390 [RFC7011] Claise, B., Trammell, B., and P. Aitken, "Specification of 391 the IP Flow Information Export (IPFIX) Protocol for the 392 Exchange of Flow Information", STD 77, RFC 7011, September 393 2013. 395 8.2. Informative References 397 [I-D.ietf-lmap-framework] 398 Eardley, P., Morton, A., Bagnulo, M., Burbridge, T., 399 Aitken, P., and A. Akhter, "A framework for Large-Scale 400 Measurement of Broadband Performance (LMAP)", draft-ietf- 401 lmap-framework-11 (work in progress), February 2015. 403 [I-D.elkins-ippm-pdm-option] 404 Elkins, N. and M. Ackermann, "IPPM Considerations for the 405 IPv6 PDM Destination Option", draft-elkins-ippm-pdm- 406 option-03 (work in progress), February 2015. 408 [I-D.tempia-opsawg-p3m] 409 Capello, A., Cociglio, M., Castaldelli, L., and A. Bonda, 410 "A packet based method for passive performance 411 monitoring", draft-tempia-opsawg-p3m-04 (work in 412 progress), February 2014. 414 [I-D.chen-ippm-coloring-based-ipfpm-framework] 415 Chen, M., Zheng, L., Mirsky, G., and G. Fioccola, "IP Flow 416 Performance Measurement Framework", draft-chen-ippm- 417 coloring-based-ipfpm-framework-03 (work in progress), 418 February 2015. 420 Author's Address 422 Al Morton 423 AT&T Labs 424 200 Laurel Avenue South 425 Middletown, NJ 426 USA 428 Email: acmorton@att.com