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Checking references for intended status: Experimental ---------------------------------------------------------------------------- == Outdated reference: A later version (-12) exists of draft-ietf-bier-mpls-encapsulation-07 == Outdated reference: A later version (-15) exists of draft-ietf-bier-pmmm-oam-02 == Outdated reference: A later version (-07) exists of draft-ietf-mpls-flow-ident-05 == Outdated reference: A later version (-10) exists of draft-ietf-mpls-rfc6374-sfl-00 == Outdated reference: A later version (-12) exists of draft-ietf-nvo3-encap-00 Summary: 0 errors (**), 0 flaws (~~), 6 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group G. Fioccola, Ed. 3 Internet-Draft A. Capello 4 Intended status: Experimental M. Cociglio 5 Expires: March 15, 2018 L. Castaldelli 6 Telecom Italia 7 M. Chen 8 L. Zheng 9 Huawei Technologies 10 G. Mirsky 11 ZTE 12 T. Mizrahi 13 Marvell 14 September 11, 2017 16 Alternate Marking method for passive and hybrid performance monitoring 17 draft-ietf-ippm-alt-mark-10 19 Abstract 21 This document describes a method to perform packet loss, delay and 22 jitter measurements on live traffic. This method is based on 23 Alternate Marking (Coloring) technique. A report is provided in 24 order to explain an example and show the method applicability. This 25 technique can be applied in various situations as detailed in this 26 document and could be considered passive or hybrid depending on the 27 application. 29 Requirements Language 31 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 32 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 33 "OPTIONAL" in this document are to be interpreted as described in BCP 34 14 [RFC2119] [RFC8174] when, and only when, they appear in all 35 capitals, as shown here. 37 Status of This Memo 39 This Internet-Draft is submitted in full conformance with the 40 provisions of BCP 78 and BCP 79. 42 Internet-Drafts are working documents of the Internet Engineering 43 Task Force (IETF). Note that other groups may also distribute 44 working documents as Internet-Drafts. The list of current Internet- 45 Drafts is at https://datatracker.ietf.org/drafts/current/. 47 Internet-Drafts are draft documents valid for a maximum of six months 48 and may be updated, replaced, or obsoleted by other documents at any 49 time. It is inappropriate to use Internet-Drafts as reference 50 material or to cite them other than as "work in progress." 52 This Internet-Draft will expire on March 15, 2018. 54 Copyright Notice 56 Copyright (c) 2017 IETF Trust and the persons identified as the 57 document authors. All rights reserved. 59 This document is subject to BCP 78 and the IETF Trust's Legal 60 Provisions Relating to IETF Documents 61 (https://trustee.ietf.org/license-info) in effect on the date of 62 publication of this document. Please review these documents 63 carefully, as they describe your rights and restrictions with respect 64 to this document. Code Components extracted from this document must 65 include Simplified BSD License text as described in Section 4.e of 66 the Trust Legal Provisions and are provided without warranty as 67 described in the Simplified BSD License. 69 Table of Contents 71 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 72 2. Overview of the method . . . . . . . . . . . . . . . . . . . 4 73 3. Detailed description of the method . . . . . . . . . . . . . 6 74 3.1. Packet loss measurement . . . . . . . . . . . . . . . . . 6 75 3.1.1. Coloring the packets . . . . . . . . . . . . . . . . 11 76 3.1.2. Counting the packets . . . . . . . . . . . . . . . . 11 77 3.1.3. Collecting data and calculating packet loss . . . . . 12 78 3.2. Timing aspects . . . . . . . . . . . . . . . . . . . . . 12 79 3.3. One-way delay measurement . . . . . . . . . . . . . . . . 14 80 3.3.1. Single marking methodology . . . . . . . . . . . . . 14 81 3.3.2. Double marking methodology . . . . . . . . . . . . . 16 82 3.4. Delay variation measurement . . . . . . . . . . . . . . . 17 83 4. Considerations . . . . . . . . . . . . . . . . . . . . . . . 18 84 4.1. Synchronization . . . . . . . . . . . . . . . . . . . . . 18 85 4.2. Data Correlation . . . . . . . . . . . . . . . . . . . . 18 86 4.3. Packet Re-ordering . . . . . . . . . . . . . . . . . . . 19 87 5. Implementation and deployment . . . . . . . . . . . . . . . . 20 88 5.1. Report on the operational experiment at Telecom Italia . 20 89 5.1.1. Metric transparency . . . . . . . . . . . . . . . . . 22 90 5.2. IP flow performance measurement (IPFPM) . . . . . . . . . 22 91 5.3. OAM Passive Performance Measurement . . . . . . . . . . . 22 92 5.4. RFC6374 Use Case . . . . . . . . . . . . . . . . . . . . 23 93 5.5. Application to active performance measurement . . . . . . 23 94 6. Hybrid measurement . . . . . . . . . . . . . . . . . . . . . 23 95 7. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 96 8. Compliance with RFC6390 guidelines . . . . . . . . . . . . . 24 97 9. Security Considerations . . . . . . . . . . . . . . . . . . . 26 98 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 99 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27 100 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 27 101 12.1. Normative References . . . . . . . . . . . . . . . . . . 27 102 12.2. Informative References . . . . . . . . . . . . . . . . . 28 103 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30 105 1. Introduction 107 Nowadays, most Service Providers' networks carry traffic with 108 contents that are highly sensitive to packet loss [RFC7680], delay 109 [RFC7679], and jitter [RFC3393]. 111 In view of this scenario, Service Providers need methodologies and 112 tools to monitor and measure network performances with an adequate 113 accuracy, in order to constantly control the quality of experience 114 perceived by their customers. On the other hand, performance 115 monitoring provides useful information for improving network 116 management (e.g. isolation of network problems, troubleshooting, 117 etc.). 119 A lot of work related to OAM, that includes also performance 120 monitoring techniques, has been done by Standards Developing 121 Organizations(SDOs): [RFC7276] provides a good overview of existing 122 OAM mechanisms defined in IETF, ITU-T and IEEE. Considering IETF, a 123 lot of work has been done on fault detection and connectivity 124 verification, while a minor effort has been dedicated so far to 125 performance monitoring. The IPPM WG has defined standard metrics to 126 measure network performance; however, the methods developed in this 127 WG mainly refer to focus on active measurement techniques. More 128 recently, the MPLS WG has defined mechanisms for measuring packet 129 loss, one-way and two-way delay, and delay variation in MPLS 130 networks[RFC6374], but their applicability to passive measurements 131 has some limitations, especially for pure connection-less networks. 133 The lack of adequate tools to measure packet loss with the desired 134 accuracy drove an effort to design a new method for the performance 135 monitoring of live traffic, possibly easy to implement and deploy. 136 The effort led to the method described in this document: basically, 137 it is a passive performance monitoring technique, potentially 138 applicable to any kind of packet based traffic, including Ethernet, 139 IP, and MPLS, both unicast and multicast. The method addresses 140 primarily packet loss measurement, but it can be easily extended to 141 one-way delay and delay variation measurements as well. 143 The method has been explicitly designed for passive measurements but 144 it can also be used with active probes. Passive measurements are 145 usually more easily understood by customers and provide a much better 146 accuracy, especially for packet loss measurements. 148 RFC 7799 [RFC7799] defines passive and hybrid methods of measurement. 149 In particular, Passive Methods of Measurement are based solely on 150 observations of an undisturbed and unmodified packet stream of 151 interest; Hybrid Methods are Methods of Measurement that use a 152 combination of Active Methods and Passive Methods. 154 Taking into consideration these definitions, Alternate Marking Method 155 could be considered Hybrid or Passive depending on the case. In case 156 the marking field is obtained by changing existing field values of 157 the packets (e.g. DSCP field), the technique is Hybrid. In case the 158 marking field is dedicated, reserved and is included in the protocol 159 specification Alternate Marking technique can be considered as 160 Passive (e.g. RFC6374 Synonymous Flow Label or OAM Marking Bits in 161 BIER Header). 163 This document is organized as follows: 165 o Section 2 gives an overview of the method, including a comparison 166 with different measurement strategies; 168 o Section 3 describes the method in detail; 170 o Section 4 reports considerations about synchronization, data 171 correlation and packet re-ordering; 173 o Section 5 reports examples of implementation and deployment of the 174 method. Furthermore the operational experiment done at Telecom 175 Italia is described; 177 o Section 6 introduces Hybrid measurement aspects; 179 o Section 7 is about the Compliance with RFC6390 guidelines; 181 o Section 8 includes some security aspects; 183 o Section 9 finally summarizes some concluding remarks. 185 2. Overview of the method 187 In order to perform packet loss measurements on a live traffic flow, 188 different approaches exist. The most intuitive one consists in 189 numbering the packets, so that each router that receives the flow can 190 immediately detect a packet missing. This approach, though very 191 simple in theory, is not simple to achieve: it requires the insertion 192 of a sequence number into each packet and the devices must be able to 193 extract the number and check it in real time. Such a task can be 194 difficult to implement on live traffic: if UDP is used as the 195 transport protocol, the sequence number is not available; on the 196 other hand, if a higher layer sequence number (e.g. in the RTP 197 header) is used, extracting that information from each packet and 198 process it in real time could overload the device. 200 An alternate approach is to count the number of packets sent on one 201 end, the number of packets received on the other end, and to compare 202 the two values. This operation is much simpler to implement, but 203 requires that the devices performing the measurement are in sync: in 204 order to compare two counters it is required that they refer exactly 205 to the same set of packets. Since a flow is continuous and cannot be 206 stopped when a counter has to be read, it could be difficult to 207 determine exactly when to read the counter. A possible solution to 208 overcome this problem is to virtually split the flow in consecutive 209 blocks by inserting periodically a delimiter so that each counter 210 refers exactly to the same block of packets. The delimiter could be 211 for example a special packet inserted artificially into the flow. 212 However, delimiting the flow using specific packets has some 213 limitations. First, it requires generating additional packets within 214 the flow and requires the equipment to be able to process those 215 packets. In addition, the method is vulnerable to out of order 216 reception of delimiting packets and, to a lesser extent, to their 217 loss. 219 The method proposed in this document follows the second approach, but 220 it doesn't use additional packets to virtually split the flow in 221 blocks. Instead, it "marks" the packets so that the packets 222 belonging to the same block will have the same color, whilst 223 consecutive blocks will have different colors. Each change of color 224 represents a sort of auto-synchronization signal that guarantees the 225 consistency of measurements taken by different devices along the path 226 (see also [I-D.cociglio-mboned-multicast-pm] and 227 [I-D.tempia-opsawg-p3m], where this technique was introduced). 229 Figure 1 represents a very simple network and shows how the method 230 can be used to measure packet loss on different network segments: by 231 enabling the measurement on several interfaces along the path, it is 232 possible to perform link monitoring, node monitoring or end-to-end 233 monitoring. The method is flexible enough to measure packet loss on 234 any segment of the network and can be used to isolate the faulty 235 element. 237 Traffic flow 238 ========================================================> 239 +------+ +------+ +------+ +------+ 240 ---<> R1 <>-----<> R2 <>-----<> R3 <>-----<> R4 <>--- 241 +------+ +------+ +------+ +------+ 242 . . . . . . 243 . . . . . . 244 . <------> <-------> . 245 . Node Packet Loss Link Packet Loss . 246 . . 247 <---------------------------------------------------> 248 End-to-End Packet loss 250 Figure 1: Available measurements 252 3. Detailed description of the method 254 This section describes in detail how the method operate. A special 255 emphasis is given to the measurement of packet loss, that represents 256 the core application of the method, but applicability to delay and 257 jitter measurements is also considered. 259 3.1. Packet loss measurement 261 The basic idea is to virtually split traffic flows into consecutive 262 blocks: each block represents a measurable entity unambiguously 263 recognizable by all network devices along the path. By counting the 264 number of packets in each block and comparing the values measured by 265 different network devices along the path, it is possible to measure 266 packet loss occurred in any single block between any two points. 268 As discussed in the previous section, a simple way to create the 269 blocks is to "color" the traffic (two colors are sufficient) so that 270 packets belonging to different consecutive blocks will have different 271 colors. Whenever the color changes, the previous block terminates 272 and the new one begins. Hence, all the packets belonging to the same 273 block will have the same color and packets of different consecutive 274 blocks will have different colors. The number of packets in each 275 block depends on the criterion used to create the blocks: 277 o if the color is switched after a fixed number of packets, then 278 each block will contain the same number of packets (except for any 279 losses); 281 o if the color is switched according to a fixed timer, then the 282 number of packets may be different in each block depending on the 283 packet rate. 285 The following figure shows how a flow looks like when it is split in 286 traffic blocks with colored packets. 288 A: packet with A coloring 289 B: packet with B coloring 291 | | | | | 292 | | Traffic flow | | 293 -------------------------------------------------------------------> 294 BBBBBBB AAAAAAAAAAA BBBBBBBBBBB AAAAAAAAAAA BBBBBBBBBBB AAAAAAA 295 -------------------------------------------------------------------> 296 ... | Block 5 | Block 4 | Block 3 | Block 2 | Block 1 297 | | | | | 299 Figure 2: Traffic coloring 301 Figure 3 shows how the method can be used to measure link packet loss 302 between two adjacent nodes. 304 Referring to the figure, let's assume we want to monitor the packet 305 loss on the link between two routers: router R1 and router R2. 306 According to the method, the traffic is colored alternatively with 307 two different colors, A and B. Whenever the color changes, the 308 transition generates a sort of square-wave signal, as depicted in the 309 following figure. 311 Color A ----------+ +-----------+ +---------- 312 | | | | 313 Color B +-----------+ +-----------+ 314 Block n ... Block 3 Block 2 Block 1 315 <---------> <---------> <---------> <---------> <---------> 317 Traffic flow 318 ===========================================================> 319 Color ...AAAAAAAAAAA BBBBBBBBBBB AAAAAAAAAAA BBBBBBBBBBB AAAAAAA... 320 ===========================================================> 322 Figure 3: Computation of link packet loss 324 Traffic coloring could be done by R1 itself or by an upward router. 325 R1 needs two counters, C(A)R1 and C(B)R1, on its egress interface: 326 C(A)R1 counts the packets with color A and C(B)R1 counts those with 327 color B. As long as traffic is colored A, only counter C(A)R1 will 328 be incremented, while C(B)R1 is not incremented; vice versa, when the 329 traffic is colored as B, only C(B)R1 is incremented. C(A)R1 and 330 C(B)R1 can be used as reference values to determine the packet loss 331 from R1 to any other measurement point down the path. Router R2, 332 similarly, will need two counters on its ingress interface, C(A)R2 333 and C(B)R2, to count the packets received on that interface and 334 colored with color A and B respectively. When an A block ends, it is 335 possible to compare C(A)R1 and C(A)R2 and calculate the packet loss 336 within the block; similarly, when the successive B block terminates, 337 it is possible to compare C(B)R1 with C(B)R2, and so on for every 338 successive block. 340 Likewise, by using two counters on R2 egress interface it is possible 341 to count the packets sent out of R2 interface and use them as 342 reference values to calculate the packet loss from R2 to any 343 measurement point down R2. 345 Using a fixed timer for color switching offers a better control over 346 the method: the (time) length of the blocks can be chosen large 347 enough to simplify the collection and the comparison of measures 348 taken by different network devices. It's preferable to read the 349 value of the counters not immediately after the color switch: some 350 packets could arrive out of order and increment the counter 351 associated to the previous block (color), so it is worth waiting for 352 some time. A safe choice is to wait L/2 time units (where L is the 353 duration for each block) after the color switch, to read the still 354 counter of the previous color, so the possibility to read a running 355 counter instead of a still one is minimized. The drawback is that 356 the longer the duration of the block, the less frequent the 357 measurement can be taken. 359 The following table shows how the counters can be used to calculate 360 the packet loss between R1 and R2. The first column lists the 361 sequence of traffic blocks while the other columns contain the 362 counters of A-colored packets and B-colored packets for R1 and R2. 363 In this example, we assume that the values of the counters are reset 364 to zero whenever a block ends and its associated counter has been 365 read: with this assumption, the table shows only relative values, 366 that is the exact number of packets of each color within each block. 367 If the values of the counters were not reset, the table would contain 368 cumulative values, but the relative values could be determined simply 369 by difference from the value of the previous block of the same color. 371 The color is switched on the basis of a fixed timer (not shown in the 372 table), so the number of packets in each block is different. 374 +-------+--------+--------+--------+--------+------+ 375 | Block | C(A)R1 | C(B)R1 | C(A)R2 | C(B)R2 | Loss | 376 +-------+--------+--------+--------+--------+------+ 377 | 1 | 375 | 0 | 375 | 0 | 0 | 378 | | | | | | | 379 | 2 | 0 | 388 | 0 | 388 | 0 | 380 | | | | | | | 381 | 3 | 382 | 0 | 381 | 0 | 1 | 382 | | | | | | | 383 | 4 | 0 | 377 | 0 | 374 | 3 | 384 | | | | | | | 385 | ... | ... | ... | ... | ... | ... | 386 | | | | | | | 387 | 2n | 0 | 387 | 0 | 387 | 0 | 388 | | | | | | | 389 | 2n+1 | 379 | 0 | 377 | 0 | 2 | 390 +-------+--------+--------+--------+--------+------+ 392 Table 1: Evaluation of counters for packet loss measurements 394 During an A block (blocks 1, 3 and 2n+1), all the packets are 395 A-colored, therefore the C(A) counters are incremented to the number 396 seen on the interface, while C(B) counters are zero. Vice versa, 397 during a B block (blocks 2, 4 and 2n), all the packets are B-colored: 398 C(A) counters are zero, while C(B) counters are incremented. 400 When a block ends (because of color switching) the relative counters 401 stop incrementing and it is possible to read them, compare the values 402 measured on router R1 and R2 and calculate the packet loss within 403 that block. 405 For example, looking at the table above, during the first block 406 (A-colored), C(A)R1 and C(A)R2 have the same value (375), which 407 corresponds to the exact number of packets of the first block (no 408 loss). Also during the second block (B-colored) R1 and R2 counters 409 have the same value (388), which corresponds to the number of packets 410 of the second block (no loss). During blocks three and four, R1 and 411 R2 counters are different, meaning that some packets have been lost: 412 in the example, one single packet (382-381) was lost during block 413 three and three packets (377-374) were lost during block four. 415 The method applied to R1 and R2 can be extended to any other router 416 and applied to more complex networks, as far as the measurement is 417 enabled on the path followed by the traffic flow(s) being observed. 419 It's worth mentioning two different strategies that can be used when 420 implementing the method: 422 o flow-based: the flow-based strategy is used when only a limited 423 number of traffic flows need to be monitored. According to this 424 strategy, only a subset of the flows is colored. Counters for 425 packet loss measurements can be instantiated for each single flow, 426 or for the set as a whole, depending on the desired granularity. 427 A relevant problem with this approach is the necessity to know in 428 advance the path followed by flows that are subject to 429 measurement. Path rerouting and traffic load-balancing increase 430 the issue complexity, especially for unicast traffic. The problem 431 is easier to solve for multicast traffic where load balancing is 432 seldom used and static joins are frequently used to force traffic 433 forwarding and replication. 435 o link-based: measurements are performed on all the traffic on a 436 link by link basis. The link could be a physical link or a 437 logical link. Counters could be instantiated for the traffic as a 438 whole or for each traffic class (in case it is desired to monitor 439 each class separately), but in the second case a couple of 440 counters is needed for each class. 442 As mentioned, the flow-based measurement requires the identification 443 of the flow to be monitored and the discovery of the path followed by 444 the selected flow. It is possible to monitor a single flow or 445 multiple flows grouped together, but in this case measurement is 446 consistent only if all the flows in the group follow the same path. 447 Moreover if a measurement is performed by grouping many flows, it is 448 not possible to determine exactly which flow was affected by packets 449 loss. In order to have measures per single flow it is necessary to 450 configure counters for each specific flow. Once the flow(s) to be 451 monitored have been identified, it is necessary to configure the 452 monitoring on the proper nodes. Configuring the monitoring means 453 configuring the rule to intercept the traffic and configuring the 454 counters to count the packets. To have just an end-to-end 455 monitoring, it is sufficient to enable the monitoring on the first 456 and the last hop routers of the path: the mechanism is completely 457 transparent to intermediate nodes and independent from the path 458 followed by traffic flows. On the contrary, to monitor the flow on a 459 hop-by-hop basis along its whole path it is necessary to enable the 460 monitoring on every node from the source to the destination. In case 461 the exact path followed by the flow is not known a priori (i.e. the 462 flow has multiple paths to reach the destination) it is necessary to 463 enable the monitoring system on every path: counters on interfaces 464 traversed by the flow will report packet count, counters on other 465 interfaces will be null. 467 3.1.1. Coloring the packets 469 The coloring operation is fundamental in order to create packet 470 blocks. This implies choosing where to activate the coloring and how 471 to color the packets. 473 In case of flow-based measurements, it is desirable, in general, to 474 have a single coloring node because it is easier to manage and 475 doesn't rise any risk of conflict (consider the case where two nodes 476 color the same flow). Thus it is advantageous to color the flow as 477 close as possible to the source. In addition, coloring a flow close 478 to the source allows an end-to-end measure if a measurement point is 479 enabled on the last-hop router as well. The only requirement is that 480 the coloring must change periodically and every node along the path 481 must be able to identify unambiguously the colored packets. For 482 link-based measurements, all traffic needs to be colored when 483 transmitted on the link. If the traffic had already been colored, 484 then it has to be re-colored because the color must be consistent on 485 the link. This means that each hop along the path must (re-)color 486 the traffic; the color is not required to be consistent along 487 different links. 489 Traffic coloring can be implemented by setting a specific bit in the 490 packet header and changing the value of that bit periodically. How 491 to choose the marking field depends on the application and is out of 492 scope here. 494 3.1.2. Counting the packets 496 Assuming that the coloring of the packets is performed only by the 497 source node, the nodes between source and destination (included) have 498 to count the colored packets that they receive and forward: this 499 operation can be enabled on every router along the path or only on a 500 subset, depending on which network segment is being monitored (a 501 single link, a particular metro area, the backbone, the whole path). 503 Since the color switches periodically between two values, two 504 counters (one for each value) are needed: one counter for packets 505 with color A and one counter for packets with color B. For each flow 506 (or group of flows) being monitored and for every interface where the 507 monitoring is active, a couple of counters is needed. For example, 508 in order to monitor separately 3 flows on a router with 4 interfaces 509 involved, 24 counters are needed (2 counters for each of the 3 flows 510 on each of the 4 interfaces). 512 In case of link-based measurements the behaviour is similar except 513 that coloring and counting operations are performed on a link by link 514 basis at each endpoint of the link. 516 Another important aspect to take into consideration is when to read 517 the counters: in order to count the exact number of packets of a 518 block the routers must perform this operation when that block has 519 ended: in other words, the counter for color A must be read when the 520 current block has color B, in order to be sure that the value of the 521 counter is stable. This task can be accomplished in two ways. The 522 general approach suggests to read the counters periodically, many 523 times during a block duration, and to compare these successive 524 readings: when the counter stops incrementing means that the current 525 block has ended and its value can be elaborated safely. 526 Alternatively, if the coloring operation is performed on the basis of 527 a fixed timer, it is possible to configure the reading of the 528 counters according to that timer: for example, reading the counter 529 for color A every period in the middle of the subsequent block with 530 color B is a safe choice. A sufficient margin should be considered 531 between the end of a block and the reading of the counter, in order 532 to take into account any out-of-order packets. 534 3.1.3. Collecting data and calculating packet loss 536 The nodes enabled to perform performance monitoring collect the value 537 of the counters, but they are not able to directly use this 538 information to measure packet loss, because they only have their own 539 samples. For this reason, an external Network Management System 540 (NMS) can be used to collect and elaborate data and to perform packet 541 loss calculation. The NMS compares the values of counters from 542 different nodes and can calculate if some packets were lost (even a 543 single packet) and also where packets were lost. 545 The value of the counters needs to be transmitted to the NMS as soon 546 as it has been read. This can be accomplished by using SNMP or FTP 547 and can be done in Push Mode or Polling Mode. In the first case, 548 each router periodically sends the information to the NMS, in the 549 latter case it is the NMS that periodically polls routers to collect 550 information. In any case, the NMS has to collect all the relevant 551 values from all the routers within one cycle of the timer. 553 If link-based measurement is used, it would be possible to use a 554 protocol to exchange values of counters between the two endpoints in 555 order to let them perform the packet loss calculation for each 556 traffic direction. A similar approach could be also applied to a 557 flow-based measurement. 559 3.2. Timing aspects 561 This document introduces two color switching method: one is based on 562 fixed number of packet, the other is based on fixed timer. But the 563 method based on fixed timer is preferable because is more 564 deterministic, and will be considered in the rest of the dcoument. 566 By considering the clock error between network devices R1 and R2, 567 they must be synchronized to the same clock reference with an 568 accuracy of +/- L/2 time units, where L is the time duration of the 569 block. So each colored packet can be assigned to the right batch by 570 each router. This is because the minimum time distance between two 571 packets of the same color but belonging to different batches is L 572 time units. 574 In practice, there are also out of order at batch boundaries, 575 strictly related to the delay between measurement points. This means 576 that, without considering clock error, we wait L/2 after color 577 switching to be sure to take a still counter. 579 In summary we need to take into account two contributions: clock 580 error between network devices and the interval we need to wait to 581 avoid out of order because of network delay. 583 The following figure explains both issues. 585 ...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB... 586 |<======================================>| 587 | L | 588 ...=========>|<==================><==================>|<==========... 589 | L/2 L/2 | 590 |<===>| |<===>| 591 d | | d 592 |<==========================>| 593 available counting interval 595 Figure 4: Timing aspects 597 It is assumed that all network devices are synchronized to a common 598 reference time with an accuracy of +/- A/2. Thus, the difference 599 between the clock values of any two network devices is bounded by A. 601 The guardband d is given by: 603 d = A + D_max - D_min, 605 where A is the clock accuracy, D_max is an upper bound on the network 606 delay between the network devices, and D_min is a lower bound on the 607 delay. 609 The available counting interval is L - 2d that must be > 0. 611 The condition that must be satisfied and is a requirement on the 612 synchronization accuracy is: 614 d < L/2. 616 3.3. One-way delay measurement 618 The same principle used to measure packet loss can be applied also to 619 one-way delay measurement. There are three alternatives, as 620 described hereinafter. 622 3.3.1. Single marking methodology 624 The alternation of colors can be used as a time reference to 625 calculate the delay. Whenever the color changes (that means that a 626 new block has started) a network device can store the timestamp of 627 the first packet of the new block; that timestamp can be compared 628 with the timestamp of the same packet on a second router to compute 629 packet delay. Considering Figure 2, R1 stores a timestamp TS(A1)R1 630 when it sends the first packet of block 1 (A-colored), a timestamp 631 TS(B2)R1 when it sends the first packet of block 2 (B-colored) and so 632 on for every other block. R2 performs the same operation on the 633 receiving side, recording TS(A1)R2, TS(B2)R2 and so on. Since the 634 timestamps refer to specific packets (the first packet of each block) 635 we are sure that timestamps compared to compute delay refer to the 636 same packets. By comparing TS(A1)R1 with TS(A1)R2 (and similarly 637 TS(B2)R1 with TS(B2)R2 and so on) it is possible to measure the delay 638 between R1 and R2. In order to have more measurements, it is 639 possible to take and store more timestamps, referring to other 640 packets within each block. 642 In order to coherently compare timestamps collected on different 643 routers, the clocks on the network nodes must be in sync. 644 Furthermore, a measurement is valid only if no packet loss occurs and 645 if packet misordering can be avoided, otherwise the first packet of a 646 block on R1 could be different from the first packet of the same 647 block on R2 (f.i. if that packet is lost between R1 and R2 or it 648 arrives after the next one). 650 The following table shows how timestamps can be used to calculate the 651 delay between R1 and R2. The first column lists the sequence of 652 blocks while other columns contain the timestamp referring to the 653 first packet of each block on R1 and R2. The delay is computed as a 654 difference between timestamps. For the sake of simplicity, all the 655 values are expressed in milliseconds. 657 +-------+---------+---------+---------+---------+-------------+ 658 | Block | TS(A)R1 | TS(B)R1 | TS(A)R2 | TS(B)R2 | Delay R1-R2 | 659 +-------+---------+---------+---------+---------+-------------+ 660 | 1 | 12.483 | - | 15.591 | - | 3.108 | 661 | | | | | | | 662 | 2 | - | 6.263 | - | 9.288 | 3.025 | 663 | | | | | | | 664 | 3 | 27.556 | - | 30.512 | - | 2.956 | 665 | | | | | | | 666 | | - | 18.113 | - | 21.269 | 3.156 | 667 | | | | | | | 668 | ... | ... | ... | ... | ... | ... | 669 | | | | | | | 670 | 2n | 77.463 | - | 80.501 | - | 3.038 | 671 | | | | | | | 672 | 2n+1 | - | 24.333 | - | 27.433 | 3.100 | 673 +-------+---------+---------+---------+---------+-------------+ 675 Table 2: Evaluation of timestamps for delay measurements 677 The first row shows timestamps taken on R1 and R2 respectively and 678 referring to the first packet of block 1 (which is A-colored). Delay 679 can be computed as a difference between the timestamp on R2 and the 680 timestamp on R1. Similarly, the second row shows timestamps (in 681 milliseconds) taken on R1 and R2 and referring to the first packet of 682 block 2 (which is B-colored). Comparing timestamps taken on 683 different nodes in the network and referring to the same packets 684 (identified using the alternation of colors) it is possible to 685 measure delay on different network segments. 687 For the sake of simplicity, in the above example a single measurement 688 is provided within a block, taking into account only the first packet 689 of each block. The number of measurements can be easily increased by 690 considering multiple packets in the block: for instance, a timestamp 691 could be taken every N packets, thus generating multiple delay 692 measurements. Taking this to the limit, in principle the delay could 693 be measured for each packet, by taking and comparing the 694 corresponding timestamps (possible but impractical from an 695 implementation point of view). 697 3.3.1.1. Mean delay 699 As mentioned before, the method previously exposed for measuring the 700 delay is sensitive to out of order reception of packets. In order to 701 overcome this problem, a different approach has been considered: it 702 is based on the concept of mean delay. The mean delay is calculated 703 by considering the average arrival time of the packets within a 704 single block. The network device locally stores a timestamp for each 705 packet received within a single block: summing all the timestamps and 706 dividing by the total number of packets received, the average arrival 707 time for that block of packets can be calculated. By subtracting the 708 average arrival times of two adjacent devices it is possible to 709 calculate the mean delay between those nodes. When computing the 710 mean delay, measurement error could be augmented by accumulating 711 measurement error of a lot of packets. This method is robust to out 712 of order packets and also to packet loss (only a small error is 713 introduced). Moreover, it greatly reduces the number of timestamps 714 (only one per block for each network device) that have to be 715 collected by the management system. On the other hand, it only gives 716 one measure for the duration of the block (f.i. 5 minutes), and it 717 doesn't give the minimum, maximum and median delay values (RFC 6703 718 [RFC6703]). This limitation could be overcome by reducing the 719 duration of the block (f.i. from 5 minutes to a few seconds), that 720 implicates an highly optimized implementation of the method. 722 By summing the mean delays of the two directions of a path, it is 723 also possible to measure the two-way mean delay (round-trip delay). 725 3.3.2. Double marking methodology 727 The Single marking methodology for one-way delay measurement is 728 sensitive to out of order reception of packets. The first approach 729 to overcome this problem is described before and is based on the 730 concept of mean delay. But the limitation of mean delay is that it 731 doesn't give information about the delay values distribution for the 732 duration of the block. Additionally it may be useful to have not 733 only the mean delay but also the minimum, maximum and median delay 734 values and, in wider terms, to know more about the statistic 735 distribution of delay values. So in order to have more information 736 about the delay and to overcome out of order issues, a different 737 approach can be introduced: it is based on double marking 738 methodology. 740 Basically, the idea is to use the first marking to create the 741 alternate flow and, within this colored flow, a second marking to 742 select the packets for measuring delay/jitter. The first marking is 743 needed for packet loss and mean delay measurement. The second 744 marking creates a new set of marked packets that are fully identified 745 over the network, so that a network device can store the timestamps 746 of these packets; these timestamps can be compared with the 747 timestamps of the same packets on a second router to compute packet 748 delay values for each packet. The number of measurements can be 749 easily increased by changing the frequency of the second marking. 750 But the frequency of the second marking must be not too high in order 751 to avoid out of order issues. Between packets with the second 752 marking there should be a security time gap (e.g. this gap could be, 753 at the minimum, the mean network delay calculated with the previous 754 methodology) to avoid out of order issues and also to have a number 755 of measurement packets that is rate independent. If a second marking 756 packet is lost, the delay measurement for the considered block is 757 corrupted and should be discarded. 759 Mean delay is calculated on all the packets of a sample and is a 760 simple computation to be performed for single marking method. In 761 some cases the mean delay measure is not sufficient to characterize 762 the sample, and more statistics of delay extent data are needed, e.g. 763 percentiles, variance and median delay values. The conventional 764 range (maximum-minimum) should be avoided for several reasons, 765 including stability of the maximum delay due to the influence by 766 outliers. RFC 5481 [RFC5481] section 6.5 highlights how the 99.9th 767 percentile of delay and delay variation is more helpful to 768 performance planners. To overcome this drawback the idea is to 769 couple the mean delay measure for the entire batch with double 770 marking method, where a subset of batch packets are selected for 771 extensive delay calculation by using a second marking. In this way 772 it is possible to perform a detailed analysis on these double marked 773 packets. Please note that there are classic algorithms for median 774 and variance calculation, but are out of the scope of this document. 775 The comparison between the mean delay for the entire batch and the 776 mean delay on these double marked packets gives an useful information 777 since it is possible to understand if the double marking measurements 778 are actually representative of the delay trends. 780 3.4. Delay variation measurement 782 Similarly to one-way delay measurement (both for single marking and 783 double marking), the method can also be used to measure the inter- 784 arrival jitter. We refer to the definition in RFC 3393 [RFC3393]. 785 The alternation of colors, for single marking method, can be used as 786 a time reference to measure delay variations. In case of double 787 marking, the time reference is given by the second marked packets. 788 Considering the example depicted in Figure 2, R1 stores a timestamp 789 TS(A)R1 whenever it sends the first packet of a block and R2 stores a 790 timestamp TS(B)R2 whenever it receives the first packet of a block. 791 The inter-arrival jitter can be easily derived from one-way delay 792 measurement, by evaluating the delay variation of consecutive 793 samples. 795 The concept of mean delay can also be applied to delay variation, by 796 evaluating the average variation of the interval between consecutive 797 packets of the flow from R1 to R2. 799 4. Considerations 801 This section highlights some considerations about the methodology. 803 4.1. Synchronization 805 The Alternate Marking technique does not require a strong 806 synchronization, especially for packet loss and two-way delay 807 measurement. Only one-way delay measurement requires network devices 808 to have synchronized clocks. 810 The color switching is the reference for all the network devices, and 811 the only requirement to be achieved is that all network devices have 812 to recognize the right batch along the path. 814 If the length of the measurement period is L time units, then all 815 network devices must be synchronized to the same clock reference with 816 an accuracy of +/- L/2 time units (without considering network 817 delay). This level of accuracy guarantees that all network devices 818 consistently match the color bit to the correct block. For example, 819 if the color is toggeled every second (L = 1 second), then clocks 820 must be synchronized with an accuracy of +/- 0.5 second to a common 821 time reference. 823 This synchronization requirement can be satisfied even with a 824 relatively inaccurate synchronization method. This is true for 825 packet loss and two-way delay measurement, instead, for one-way delay 826 measurement clock synchronization must be accurate. 828 Therefore, a system that uses only packet loss and two-way delay 829 measurement does not require synchronization. This is because the 830 value of the clocks of network devices does not affect the 831 computation of the two-way delay measurement. 833 4.2. Data Correlation 835 Data Correlation is the mechanism to compare counters and timestamps 836 for packet loss, delay and delay variation calculation. It could be 837 performed in several ways depending on the alternate marking 838 application and use case. 840 o A possibility is to use a centralized solution using Network 841 Management System (NMS) to correlate data; 843 o Another possibility is to define a protocol based distributed 844 solution, by defining a new protocol or by extending the existing 845 protocols (e.g. RFC6374, TWAMP, OWAMP) in order to communicate 846 the counters and timestamps between nodes. 848 In the following paragraphs an example data correlation mechanism is 849 explained and could be use independently of the adopted solutions. 851 When data is collected on the upstream and downstream node, e.g., 852 packet counts for packet loss measurement or timestamps for packet 853 delay measurement, and periodically reported to or pulled by other 854 nodes or NMS, a certain data correlation mechanism SHOULD be in use 855 to help the nodes or NMS to tell whether any two or more packet 856 counts are related to the same block of markers, or any two 857 timestamps are related to the same marked packet. 859 The alternate marking method described in this document literally 860 split the packets of the measured flow into different measurement 861 blocks, in addition a Block Number could be assigned to each of such 862 measurement block. The BN is generated each time a node reads the 863 data (packet counts or timestamps), and is associated with each 864 packet count and timestamp reported to or pulled by other nodes or 865 NMS. The value of BN could be calculated as the modulo of the local 866 time (when the data are read) and the interval of the marking time 867 period. 869 When the nodes or NMS see, for example, same BNs associated with two 870 packet counts from an upstream and a downstream node respectively, it 871 considers that these two packet counts corresponding to the same 872 block, i.e. that these two packet counts belong to the same block of 873 markers from the upstream and downstream node. The assumption of 874 this BN mechanism is that the measurement nodes are time 875 synchronized. This requires the measurement nodes to have a certain 876 time synchronization capability (e.g., the Network Time Protocol 877 (NTP) RFC 5905 [RFC5905], or the IEEE 1588 Precision Time Protocol 878 (PTP) [IEEE-1588]). Synchronization aspects are further discussed in 879 Section 4. 881 4.3. Packet Re-ordering 883 Due to ECMP, packet re-ordering is very common in IP network. The 884 accuracy of marking based PM, especially packet loss measurement, may 885 be affected by packet re-ordering. Take a look at the following 886 example: 888 Block : 1 | 2 | 3 | 4 | 5 |... 889 --------|---------|---------|---------|---------|---------|--- 890 Node R1 : AAAAAAA | BBBBBBB | AAAAAAA | BBBBBBB | AAAAAAA |... 891 Node R2 : AAAAABB | AABBBBA | AAABAAA | BBBBBBA | ABAAABA |... 893 Figure 5: Packet Reordering 895 In Figure 5 the packet stream for Node R1 isn't being reordered, and 896 can be safely assigned to interval blocks, but the packet stream for 897 Node R2 is being reordered, so, looking at the packet with the marker 898 of "B" in block 3, there is no safe way to tell whether the packet 899 belongs to block 2 or block 4. 901 In general there is the need to assign packets with the marker of "B" 902 or "A" to the right interval blocks. Most of the packet re-ordering 903 occur at the edge of adjacent blocks, and they are easy to handle if 904 the interval of each block is sufficient large. Then, it can assume 905 that the packets with different marker belong to the block that they 906 are more close to. If the interval is small, it is difficult and 907 sometime impossible to determine to which block a packet belongs. 909 To choose a proper interval is important and how to choose a proper 910 interval is out of the scope of this document. But an implementation 911 SHOULD provide a way to configure the interval and allow a certain 912 degree of packet re-ordering. 914 5. Implementation and deployment 916 The methodology described in the previous sections can be applied in 917 various situations. Basically Alternate Marking technique could be 918 used in many cases for performance measurement. The only requirement 919 is to select and mark the flow to be monitored; in this way packets 920 are batched by the sender and each batch is alternately marked such 921 that can be easily recognized by the receiver. 923 An example of implementation and deployment is explained in the next 924 section, just to clarify how the method can work. 926 5.1. Report on the operational experiment at Telecom Italia 928 The method described in this document, also called PNPM (Packet 929 Network Performance Monitoring), has been invented and engineered in 930 Telecom Italia and it's currently being used in Telecom Italia's 931 network. The methodology has been applied by leveraging functions 932 and tools available on IP routers and it's currently being used to 933 monitor packet loss in some portions of Telecom Italia's network. 934 The application of the method to delay measurement is currently being 935 evaluated in Telecom Italia's labs. This section describes how the 936 features currently available on existing routing platforms can be 937 used to apply the method, in order to give an example of 938 implementation and deployment. 940 The current implementation in Telecom Italia uses the flow-based 941 strategy, as defined in section 3. The link-based strategy could be 942 applied to physical link or a logical link (e.g. Ethernet VLAN or a 943 MPLS PW). 945 The method is applied in Telecom Italia's network to multicast IPTV 946 channels or other specific traffic flows with high QoS requirements 947 (i.e. Mobile Backhauling traffic implemented with a VPN MPLS). 949 The implementation of the method by a Service Provider needs to use 950 the router features. With current router implementations, only QoS 951 related fields and features offer the required flexibility to set 952 bits in the packet header. In case a Service Provider only uses the 953 three most significant bits of the DSCP field (corresponding to IP 954 Precedence) for QoS classification and queuing, it is possible to use 955 the two less significant bits of the DSCP field (bit 0 and bit 1) to 956 implement the method without affecting QoS policies. One of the two 957 bits (bit 0) could be used to identify flows subject to traffic 958 monitoring (set to 1 if the flow is under monitoring, otherwise it is 959 set to 0), while the second (bit 1) can be used for coloring the 960 traffic (switching between values 0 and 1, corresponding to color A 961 and B) and creating the blocks. 963 In practice, coloring the traffic using the DSCP field can be 964 implemented by configuring on the router output interface an access 965 list that intercepts the flow(s) to be monitored and applies to them 966 a policy that sets the DSCP field accordingly. Since traffic 967 coloring has to be switched between the two values over time, the 968 policy needs to be modified periodically: an automatic script is used 969 to perform this task on the basis of a fixed timer. 971 In Telecom Italia's implementation the timer is set to 5 minutes: 972 this value showed to be a good compromise between measurement 973 frequency and stability of the measurement (i.e. possibility to 974 collect all the measures referring to the same block). 976 If traffic is colored using the DSCP field an access-list that 977 matches specific DSCP values can be used to count the packets of the 978 flow(s) being monitored. The access-list is installed on all the 979 routers of the path. Also, a 5 minutes timer for color switching is 980 a safe choice for reading the counters. 982 The counters are collected by using an automatic script that sends 983 out these to a Network Management System (NMS). The NMS is 984 responsible for packet loss calculation, performed by comparing the 985 values of counters from the routers along the flow(s) path. 987 5.1.1. Metric transparency 989 Since a Service Provider application is described here, the method 990 can be applied to end-to-end services supplied to Customers. So it 991 is important to highlight that the method SHOULD be transparent 992 outside the Service Provider domain. 994 In Telecom Italia's implementation the source node colors the packets 995 with a policy that is modified periodically via an automatic script 996 in order to alternate the DSCP field of the packets. The nodes 997 between source and destination (included) have to count with an 998 access-list the colored packets that they receive and forward. 1000 Moreover the destination node has an important role: the colored 1001 packets are intercepted and a policy restores and sets the DSCP field 1002 of all the packets to the initial value. In this way the metric is 1003 transparent because outside the section of the network under 1004 monitoring the traffic flow is unchanged. 1006 In such a case, thanks to this restoring technique, network elements 1007 outside the Alternate Marking monitoring domain (e.g. the two 1008 Provider Edge nodes of the Mobile Backhauling VPN MPLS) are totally 1009 anaware that packets were marked. So this restoring technique makes 1010 Alternate Marking completely transparent outside its monitoring 1011 domain. 1013 5.2. IP flow performance measurement (IPFPM) 1015 This application of marking method is described in 1016 [I-D.chen-ippm-coloring-based-ipfpm-framework]. 1018 5.3. OAM Passive Performance Measurement 1020 In [I-D.ietf-bier-mpls-encapsulation] two OAM bits from Bit Index 1021 Explicit Replication (BIER) Header are reserved for the passive 1022 performance measurement marking method. [I-D.ietf-bier-pmmm-oam] 1023 details the measurement for multicast service over BIER domain. 1025 In addition, the alternate marking method could also be used in a 1026 Service Function Chaining (SFC) domain. 1028 The application of the marking method to Network Virtualization 1029 Overlays (NVO3) protocols is a work in progress (see 1030 [I-D.ietf-nvo3-encap]). 1032 5.4. RFC6374 Use Case 1034 RFC6374 [RFC6374] uses the LM packet as the packet accounting 1035 demarcation point. Unfortunately this gives rise to a number of 1036 problems that may lead to significant packet accounting errors in 1037 certain situations. [I-D.ietf-mpls-flow-ident] discusses the desired 1038 capabilities for MPLS flow identification in order to perform a 1039 better in-band performance monitoring of user data packets. A method 1040 of accomplishing identification is Synonymous Flow Labels (SFL) 1041 introduced in [I-D.bryant-mpls-sfl-framework], while 1042 [I-D.ietf-mpls-rfc6374-sfl] describes RFC6374 performance 1043 measurements with SFL. 1045 5.5. Application to active performance measurement 1047 [I-D.fioccola-ippm-alt-mark-active] describes how to extend the 1048 existing Active Measurement Protocol, in order to implement alternate 1049 marking methodology. [I-D.fioccola-ippm-rfc6812-alt-mark-ext] 1050 describes an extension to the Cisco SLA Protocol Measurement-Type 1051 UDP-Measurement. 1053 6. Hybrid measurement 1055 The method has been explicitly designed for passive measurements but 1056 it can also be used with active measurements. In order to have both 1057 end to end measurements and intermediate measurements (hybrid 1058 measurements) two end points can exchanges artificial traffic flows 1059 and apply alternate marking over these flows. In the intermediate 1060 points artificial traffic is managed in the same way as real traffic 1061 and measured as specified before. So the application of marking 1062 method can simplify also the active measurement, as explained in 1063 [I-D.fioccola-ippm-alt-mark-active]. 1065 7. Summary 1067 The advantages of the method described in this document are: 1069 o easy implementation: it can be implemented using features already 1070 available on major routing platforms; 1072 o low computational effort: the additional load on processing is 1073 negligible; 1075 o accurate packet loss measurement: single packet loss granularity 1076 is achieved with a passive measurement; 1078 o potential applicability to any kind of packet/frame -based 1079 traffic: Ethernet, IP, MPLS, etc., both unicast and multicast; 1081 o robustness: the method can tolerate out of order packets and it's 1082 not based on "special" packets whose loss could have a negative 1083 impact; 1085 o no interoperability issues: the features required to implement the 1086 method are available on all current routing platforms. 1088 The method doesn't raise any specific need for protocol extension, 1089 but it could be further improved by means of some extension to 1090 existing protocols. Specifically, the use of DiffServ bits for 1091 coloring the packets could not be a viable solution in some cases: a 1092 standard method to color the packets for this specific application 1093 could be beneficial. 1095 8. Compliance with RFC6390 guidelines 1097 RFC6390 [RFC6390] defines a framework and a process for developing 1098 Performance Metrics for protocols above and below the IP layer (such 1099 as IP-based applications that operate over reliable or datagram 1100 transport protocols). 1102 This document doesn't aim to propose a new Performance Metric but a 1103 new method of measurement for a few Performance Metrics that have 1104 already been standardized. Nevertheless, it's worth applying 1105 [RFC6390] guidelines to the present document, in order to provide a 1106 more complete and coherent description of the proposed method. We 1107 used a subset of the Performance Metric Definition template defined 1108 by [RFC6390]. 1110 o Metric name and description: as already stated, this document 1111 doesn't propose any new Performance Metric. On the contrary, it 1112 describes a novel method for measuring packet loss [RFC7680]. The 1113 same concept, with small differences, can also be used to measure 1114 delay [RFC7679], and jitter [RFC3393]. The document mainly 1115 describes the applicability to packet loss measurement. 1117 o Method of Measurement or Calculation: according to the method 1118 described in the previous sections, the number of packets lost is 1119 calculated by subtracting the value of the counter on the source 1120 node from the value of the counter on the destination node. Both 1121 counters must refer to the same color. The calculation is 1122 performed when the value of the counters is in a steady state. 1124 o Units of Measurement: the method calculates and reports the exact 1125 number of packets sent by the source node and not received by the 1126 destination node. 1128 o Measurement Points: the measurement can be performed between 1129 adjacent nodes, on a per-link basis, or along a multi-hop path, 1130 provided that the traffic under measurement follows that path. In 1131 case of a multi-hop path, the measurements can be performed both 1132 end-to-end and hop-by-hop. 1134 o Measurement Timing: the method have a constraint on the frequency 1135 of measurements. In order to perform a measure, the counter must 1136 be in a steady state: this happens when the traffic is being 1137 colored with the alternate color; for example in the Telecom 1138 Italia application of the method the time interval is set to 5 1139 minutes. 1141 o Implementation: the Telecom Italia application of the method uses 1142 two encodings of the DSCP field to color the packets; this enables 1143 the use of policy configurations on the router to color the 1144 packets and accordingly configure the counter for each color. The 1145 path followed by traffic being measured should be known in advance 1146 in order to configure the counters along the path and be able to 1147 compare the correct values. 1149 o Use and Applications: the method can be used to measure packet 1150 loss with high precision on live traffic; moreover, by combining 1151 end-to-end and per-link measurements, the method is useful to 1152 pinpoint the single link that is experiencing loss events. 1154 o Reporting Model: the value of the counters has to be sent to a 1155 centralized management system that perform the calculations; such 1156 samples must contain a reference to the time interval they refer 1157 to, so that the management system can perform the correct 1158 correlation; the samples have to be sent while the corresponding 1159 counter is in a steady state (within a time interval), otherwise 1160 the value of the sample should be stored locally. 1162 o Dependencies: the values of the counters have to be correlated to 1163 the time interval they refer to; moreover, as far the Telecom 1164 Italia application of the method is based on DSCP values, there 1165 are significant dependencies on the usage of the DSCP field: it 1166 must be possible to rely on unused DSCP values without affecting 1167 QoS-related configuration and behavior; moreover, the intermediate 1168 nodes must not change the value of the DSCP field not to alter the 1169 measurement. 1171 o Organization of Results: the method of measurement produces 1172 singletons. 1174 o Parameters: currently, the main parameter of the method is the 1175 time interval used to alternate the colors and read the counters. 1177 9. Security Considerations 1179 This document specifies a method to perform measurements in the 1180 context of a Service Provider's network and has not been developed to 1181 conduct Internet measurements, so it does not directly affect 1182 Internet security nor applications which run on the Internet. 1183 However, implementation of this method must be mindful of security 1184 and privacy concerns. 1186 There are two types of security concerns: potential harm caused by 1187 the measurements and potential harm to the measurements. 1189 o Harm caused by the measurement: the measurements described in this 1190 document are passive, so there are no new packets injected into 1191 the network causing potential harm to the network itself and to 1192 data traffic. Nevertheless, the method implies modifications on 1193 the fly to the IP header of data packets: this must be performed 1194 in a way that doesn't alter the quality of service experienced by 1195 packets subject to measurements and that preserve stability and 1196 performance of routers doing the measurements. One of the main 1197 security threats in OAM protocols is network reconnaissance; an 1198 attacker can gather information about the network performance by 1199 passively eavesdropping to OAM messages. The advantage of the 1200 methods described in this document is that the marking bits are 1201 the only information that is exchanged between the network 1202 devices. Therefore, passive eavesdropping to data plane traffic 1203 does not allow attackers to gain information about the network 1204 performance. 1206 o Harm to the measurement: the measurements could be harmed by 1207 routers altering the marking of the packets, or by an attacker 1208 injecting artificial traffic. Authentication techniques, such as 1209 digital signatures, may be used where appropriate to guard against 1210 injected traffic attacks. Since the measurement itself may be 1211 affected by routers (or other network devices) along the path of 1212 IP packets intentionally altering the value of marking bits of 1213 packets, as mentioned above, the mechanism specified in this 1214 document can be applied just in the context of a controlled 1215 domain, and thus the routers (or other network devices) are 1216 locally administered and this type of attack can be avoided. In 1217 addition, an attacker can't gain information about network 1218 performance from a single monitoring point, and must use 1219 synchronized monitoring points at multiple points on the path, 1220 because they have to do the same kind of measurement and 1221 aggregation that Service Providers using Alternate Marking must 1222 do. 1224 The privacy concerns of network measurement are limited because the 1225 method only relies on information contained in the IP header without 1226 any release of user data. 1228 Delay attacks are another potential threat in the context of this 1229 document. Delay measurement is performed using a specific packet in 1230 each block, marked by a dedicated color bit. Therefore, a man-in- 1231 the-middle attacker can selectively induce synthetic delay only to 1232 delay-colored packets, causing systematic error in the delay 1233 measurements. As discussed in previous sections, the methods 1234 described in this document rely on an underlying time synchronization 1235 protocol. Thus, by attacking the time protocol an attacker can 1236 potentially compromise the integrity of the measurement. A detailed 1237 discussion about the threats against time protocols and how to 1238 mitigate them is presented in RFC 7384 [RFC7384]. 1240 10. IANA Considerations 1242 There are no IANA actions required. 1244 11. Acknowledgements 1246 The previous IETF drafts about this technique were: 1247 [I-D.cociglio-mboned-multicast-pm] and [I-D.tempia-opsawg-p3m]. 1249 The authors would like to thank Alberto Tempia Bonda, Domenico 1250 Laforgia, Daniele Accetta and Mario Bianchetti for their contribution 1251 to the definition and the implementation of the method. 1253 12. References 1255 12.1. Normative References 1257 [IEEE-1588] 1258 IEEE 1588-2008, "IEEE Standard for a Precision Clock 1259 Synchronization Protocol for Networked Measurement and 1260 Control Systems", July 2008. 1262 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1263 Requirement Levels", BCP 14, RFC 2119, 1264 DOI 10.17487/RFC2119, March 1997, 1265 . 1267 [RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation 1268 Metric for IP Performance Metrics (IPPM)", RFC 3393, 1269 DOI 10.17487/RFC3393, November 2002, 1270 . 1272 [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, 1273 "Network Time Protocol Version 4: Protocol and Algorithms 1274 Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, 1275 . 1277 [RFC7679] Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton, 1278 Ed., "A One-Way Delay Metric for IP Performance Metrics 1279 (IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January 1280 2016, . 1282 [RFC7680] Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton, 1283 Ed., "A One-Way Loss Metric for IP Performance Metrics 1284 (IPPM)", STD 82, RFC 7680, DOI 10.17487/RFC7680, January 1285 2016, . 1287 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1288 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1289 May 2017, . 1291 12.2. Informative References 1293 [I-D.bryant-mpls-sfl-framework] 1294 Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S., 1295 and G. Mirsky, "Synonymous Flow Label Framework", draft- 1296 bryant-mpls-sfl-framework-05 (work in progress), June 1297 2017. 1299 [I-D.chen-ippm-coloring-based-ipfpm-framework] 1300 Chen, M., Zheng, L., Mirsky, G., Fioccola, G., and T. 1301 Mizrahi, "IP Flow Performance Measurement Framework", 1302 draft-chen-ippm-coloring-based-ipfpm-framework-06 (work in 1303 progress), March 2016. 1305 [I-D.cociglio-mboned-multicast-pm] 1306 Cociglio, M., Capello, A., Bonda, A., and L. Castaldelli, 1307 "A method for IP multicast performance monitoring", draft- 1308 cociglio-mboned-multicast-pm-01 (work in progress), 1309 October 2010. 1311 [I-D.fioccola-ippm-alt-mark-active] 1312 Fioccola, G., Clemm, A., Bryant, S., Cociglio, M., 1313 Chandramouli, M., and A. Capello, "Alternate Marking 1314 Extension to Active Measurement Protocol", draft-fioccola- 1315 ippm-alt-mark-active-01 (work in progress), March 2017. 1317 [I-D.fioccola-ippm-rfc6812-alt-mark-ext] 1318 Fioccola, G., Clemm, A., Cociglio, M., Chandramouli, M., 1319 and A. Capello, "Alternate Marking Extension to Cisco SLA 1320 Protocol RFC6812", draft-fioccola-ippm-rfc6812-alt-mark- 1321 ext-01 (work in progress), March 2016. 1323 [I-D.ietf-bier-mpls-encapsulation] 1324 Wijnands, I., Rosen, E., Dolganow, A., Tantsura, J., 1325 Aldrin, S., and I. Meilik, "Encapsulation for Bit Index 1326 Explicit Replication in MPLS and non-MPLS Networks", 1327 draft-ietf-bier-mpls-encapsulation-07 (work in progress), 1328 June 2017. 1330 [I-D.ietf-bier-pmmm-oam] 1331 Mirsky, G., Zheng, L., Chen, M., and G. Fioccola, 1332 "Performance Measurement (PM) with Marking Method in Bit 1333 Index Explicit Replication (BIER) Layer", draft-ietf-bier- 1334 pmmm-oam-02 (work in progress), July 2017. 1336 [I-D.ietf-mpls-flow-ident] 1337 Bryant, S., Pignataro, C., Chen, M., Li, Z., and G. 1338 Mirsky, "MPLS Flow Identification Considerations", draft- 1339 ietf-mpls-flow-ident-05 (work in progress), July 2017. 1341 [I-D.ietf-mpls-rfc6374-sfl] 1342 Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S., 1343 Mirsky, G., and G. Fioccola, "RFC6374 Synonymous Flow 1344 Labels", draft-ietf-mpls-rfc6374-sfl-00 (work in 1345 progress), June 2017. 1347 [I-D.ietf-nvo3-encap] 1348 Boutros, S., Ganga, I., Garg, P., Manur, R., Mizrahi, T., 1349 Mozes, D., and E. Nordmark, "NVO3 Encapsulation 1350 Considerations", draft-ietf-nvo3-encap-00 (work in 1351 progress), June 2017. 1353 [I-D.tempia-opsawg-p3m] 1354 Capello, A., Cociglio, M., Castaldelli, L., and A. Bonda, 1355 "A packet based method for passive performance 1356 monitoring", draft-tempia-opsawg-p3m-04 (work in 1357 progress), February 2014. 1359 [RFC5481] Morton, A. and B. Claise, "Packet Delay Variation 1360 Applicability Statement", RFC 5481, DOI 10.17487/RFC5481, 1361 March 2009, . 1363 [RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay 1364 Measurement for MPLS Networks", RFC 6374, 1365 DOI 10.17487/RFC6374, September 2011, 1366 . 1368 [RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New 1369 Performance Metric Development", BCP 170, RFC 6390, 1370 DOI 10.17487/RFC6390, October 2011, 1371 . 1373 [RFC6703] Morton, A., Ramachandran, G., and G. Maguluri, "Reporting 1374 IP Network Performance Metrics: Different Points of View", 1375 RFC 6703, DOI 10.17487/RFC6703, August 2012, 1376 . 1378 [RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y. 1379 Weingarten, "An Overview of Operations, Administration, 1380 and Maintenance (OAM) Tools", RFC 7276, 1381 DOI 10.17487/RFC7276, June 2014, 1382 . 1384 [RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in 1385 Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384, 1386 October 2014, . 1388 [RFC7799] Morton, A., "Active and Passive Metrics and Methods (with 1389 Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799, 1390 May 2016, . 1392 Authors' Addresses 1394 Giuseppe Fioccola (editor) 1395 Telecom Italia 1396 Via Reiss Romoli, 274 1397 Torino 10148 1398 Italy 1400 Email: giuseppe.fioccola@telecomitalia.it 1402 Alessandro Capello 1403 Telecom Italia 1404 Via Reiss Romoli, 274 1405 Torino 10148 1406 Italy 1408 Email: alessandro.capello@telecomitalia.it 1409 Mauro Cociglio 1410 Telecom Italia 1411 Via Reiss Romoli, 274 1412 Torino 10148 1413 Italy 1415 Email: mauro.cociglio@telecomitalia.it 1417 Luca Castaldelli 1418 Telecom Italia 1419 Via Reiss Romoli, 274 1420 Torino 10148 1421 Italy 1423 Email: luca.castaldelli@telecomitalia.it 1425 Mach(Guoyi) Chen 1426 Huawei Technologies 1428 Email: mach.chen@huawei.com 1430 Lianshu Zheng 1431 Huawei Technologies 1433 Email: vero.zheng@huawei.com 1435 Greg Mirsky 1436 ZTE 1437 USA 1439 Email: gregimirsky@gmail.com 1441 Tal Mizrahi 1442 Marvell 1443 6 Hamada st. 1444 Yokneam 1445 Israel 1447 Email: talmi@marvell.com