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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: 'RFC8186' is defined on line 376, but no explicit reference was found in the text Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Deterministic Networking Working Group H. Yang 3 Internet-Draft P. Liu 4 Intended status: Informational China Mobile 5 Expires: 2 September 2022 1 March 2022 7 One-way Delay Measurement Based on Deterministic Networking 8 draft-yang-detnet-deterministic-owd-measurement-00 10 Abstract 12 One-way delay is a key indicator to measure network quality. Some 13 applications are one-way transmission in the network, such as some 14 high-definition video services, and are very sensitive to one-way 15 delay. Excessive delay will affect user experience greatly. To some 16 extent, the network can't even be used, so it is very important to 17 accurately measure the network transmission delay. The current one- 18 way delay measurement method has problems such as high complexity and 19 low measurement accuracy. In order to solve the problem of high- 20 precision one-way delay measurement, a one-way delay measurement 21 method based on deterministic networking is proposed in this 22 document. The method takes advantage of the delay characteristics of 23 the deterministic networking and does not depend on precise time 24 synchronization.The method realizes the one-way delay measurement of 25 any service flow between any network elements. Its technical 26 advantages are: the network does not need to send measurement 27 packets, can test all traffic types, does not change network status, 28 does not change the format of traffic packets, and does not require 29 network elements to support time synchronization protocols. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at https://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on 2 September 2022. 48 Copyright Notice 50 Copyright (c) 2022 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 55 license-info) in effect on the date of publication of this document. 56 Please review these documents carefully, as they describe your rights 57 and restrictions with respect to this document. Code Components 58 extracted from this document must include Revised BSD License text as 59 described in Section 4.e of the Trust Legal Provisions and are 60 provided without warranty as described in the Revised BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 65 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 66 2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 67 2.2. Requirements Language . . . . . . . . . . . . . . . . . . 4 68 3. One-way Delay Measurement Method Based on Deterministic 69 Networking . . . . . . . . . . . . . . . . . . . . . . . 4 70 4. Procedures of the One-way Delay Measurement Method . . . . . 7 71 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 72 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 73 7. Normative References . . . . . . . . . . . . . . . . . . . . 8 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 76 1. Introduction 78 One-way transmission delay is a key indicator to measure network 79 quality. Some applications are based on one-way transmission in the 80 network, such as some high-definition video services, and are very 81 sensitive to one-way delay. Excessive one-way delay will affect user 82 experience dramatically, so it is very important to accurately 83 measure the one-way transmission delay of the network. 85 There are several kinds of methods to measure one-way delay. The 86 first kind of methods is active measurement. A sender will send 87 measurement protocol messages, such as Two-Way Active Measurement 88 Protocol (TWAMP) [RFC8186]messages, to the network to measure the 89 one-way delay of the sender and receiver. The advantage of active 90 measurement is that it is flexible in application. The disadvantage 91 is that the measurement messages cannot measure the delay of real 92 services, and the measurement of one-way delay requires sender and 93 receiver to support time synchronization protocol, such as NTP 94 [RFC5905]and PTP [IEEE.1588.2008]. The first kind of methods is 95 passive measurement. The passive measurement devices will calculate 96 network delay by collecting actual business traffic. The advantage 97 of passive measurement is that it can measure the one-way delay of 98 real services. The disadvantage is that two passive measurement 99 devices need to be deployed, and the two devices require time 100 synchronization, which is difficult to implement. The third kind of 101 methods is hybrid measurement. Hybrid measurement is a combination 102 of active and passive measurements, that is, inserting some fields or 103 flags in the service message to realize the delay measurement of the 104 actual service. The disadvantage is that the message format of the 105 actual service is changed, which will affect the forwarding behavior 106 of the service and have observer effect. The network element needs 107 to be able to recognize and forward the modified service message, and 108 time synchronization of the network element is also required. 110 The above-mentioned one-way delay measurement methods have the 111 following shortcomings. Firstly, if the measurement message is 112 injected into actual network, it will occupy network bandwidth 113 resources and interfere with the actual service flow, so the measured 114 delay is not the delay of the actual service. Secondly, the 115 measurement equipment or network elements need to support time 116 synchronization protocols, which is difficult to implement and 117 costly. 119 To address the following shortcomings of existing methods, this 120 document presents the following technical solution. A high-precision 121 one-way delay measurement method is proposed, which can be used to 122 measure the one-way delay of actual service packets, without sending 123 measurement messages, without changing the actual network status, 124 without changing service messages, and without the need for network 125 elements to support time synchronization protocols. 127 2. Conventions Used in This Document 129 2.1. Terminology 131 NTP Network Time Protocol 133 PTP Precision Time Protocol 135 TWAMP Two-Way Active Measurement Protocol 137 SLA Service Level Agreement 139 2.2. Requirements Language 141 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 142 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 143 "OPTIONAL" in this document are to be interpreted as described in BCP 144 14[RFC2119][RFC8174] when, and only when, they appear in all 145 capitals, as shown here. 147 3. One-way Delay Measurement Method Based on Deterministic Networking 149 +-----------------------------------------------------------+ 150 | Centralized Control Node | 151 +----+-------------+---------------+---------+---------+----+ 152 ^ ^ ^ ^ ^ 153 | | T4 | T3 | | Tn 154 | | | +----+----+ | 155 | | | | Network | | 156 T1 | T2 | +----------------->Element 3+-+ | 157 | | | | | | | | 158 | | | | +---------+ | | 159 | | | | | | 160 | | | | | | 161 | | | | | | 162 | | | | | | 163 +----+----+ +----+--+-+ +----+----+ +-v--+----+ 164 | Network | | Network | | Network | | Network | 165 |Element 1+--->Element 2+----->Element 4+--------->Element n| 166 | | | | | | | | 167 +---------+ +---------+ +---------+ +---------+ 169 Figure 1: Figure 1: A schematic diagram of the network topology 170 structure 172 A schematic diagram of the network topology structure to describe the 173 proposed method is shown in Figure 1. The network may be a SDN 174 (Software Defined Network) or a traditional network. Whether it is 175 SDN or traditional network, there is a centralized control node (or 176 called a centralized management unit) for collecting network 177 information sent by network elements and sending control information 178 to the network. Taking SDN as an example, the centralized control 179 node can be a SDN controller. For traditional networks, the 180 centralized control node can be a network management system. The 181 information from the network element to the centralized control node 182 generally passes through the management network. In our solution, 183 the management network from each network element to the centralized 184 control node is required to use a delay deterministic network. As an 185 example, the delay deterministic network may be a time sensitive 186 network (TSN) or a deterministic Internet (Deterministic Internet 187 Network, DIP) [RFC8655], etc. Through the delay deterministic 188 network, the transmission delay of the network element information 189 from the network element to the centralized control node can be 190 guaranteed to be fixed. T1~Tn in Figure 1 represent the network 191 element information delay from the network element to the centralized 192 control node of network element 1 to n respectively. 194 As shown in Figure 1, suppose network traffic of a real service flow 195 passes through network element 1, network element 2, ..., network 196 element n in turn, and the time when network traffic passes through 197 the network element is recorded as t1, t2, ..., tn. The timestamp 198 maybe the ingress timestamp of network traffic entering the network 199 element or the egress timestamp of network traffic flowing out of the 200 network element after the forwarding is completed. Each network 201 element transmits the flow information to the centralized control 202 node through the delay deterministic network when real traffic 203 passes, and the transmission delays of each network element to 204 transmit the flow information to the centralized control node through 205 the delay deterministic network are denoted as T1, T2, ..., Tn, 206 respectively. The timestamps when the centralized control node 207 receives the flow information of each network element are t1', t2', 208 ..., tn'. 210 Taking the calculation of the one-way transmission delay of traffic 211 from network element 1 to network element 2 as an example, the one- 212 way transmission delay can be calculated in the following way. 213 Firstly, because the clocks of network element 1 and network element 214 2 are not synchronized, suppose the time deviation between the two is 215 delta_t. Then the one-way transmission delay of traffic from network 216 element 1 to network element 2 satisfies the following formula (1). 217 Among them, Delay represents the one-way transmission delay of 218 traffic from network element 1 to network element 2. 220 Formula (1): Delay = t2 - t1 - delta_t 222 Secondly, because the clocks between network element 1 and the 223 centralized control node are not synchronized, assuming that the time 224 deviation between the two is delta_t', the time for the traffic 225 information collected from the network element 1 to reach the 226 centralized control node through the delay deterministic network 227 satisfies the following formula (2). 229 Formula (2): t1' = t1 + T1 + delta_t' 230 Thirdly, the clocks between network element 2 and the centralized 231 control node are not synchronized, and the time deviation between 232 network element 2 and the centralized control node is delta_t'- 233 delta_t. The time t2' for the collected traffic to reach the 234 centralized control node satisfies the following formula (3). 236 Formula (3): t2' = t2 + T2 + delta_t' - delta_t 238 Forthly, subtracting the formula (2) from the above formula (3), we 239 can obtain the following formula (4). 241 Formula (4): t2 - t1 - delta_t = t2' - t1' + T1 - T2 243 Fifthly, substituting the above formula (4) into the above formula 244 (1), the following formula (5) can be obtained. 246 Formula (5): Delay = t2' - t1' + T1 - T2 248 So far, the one-way transmission delay of traffic from network 249 element 1 to network element 2 is obtained. Taking the calculation 250 of one-way transmission delay of traffic from network element 1 to 251 network element 3 as an example, the one-way transmission delay can 252 be calculated in the following way: I) Referring to the above formula 253 (5), the one-way transmission delay of traffic from network element 1 254 to network element 2 is: Delay12 = t2' - t1' + T1 - T2. II) 255 Referring to the above formula (5), the one-way transmission delay of 256 traffic from network element 2 to network element 3 is: Delay23 = t3' 257 - t2' + T2 - T3. III) The one-way transmission delay of traffic from 258 network element 1 to network element 3 is: Delay13 = Delay12 + 259 Delay23 = t2' - t1' + T1 - T2 + t3' -t2' +T2 - T3 = t3' - t1' + T1 - 260 T3. It can be seen that the one-way transmission delay between any 261 two network elements can be calculated similarly to the above formula 262 (5). For example, taking network element m and network element n as 263 an example, the transmission delay of traffic from network element m 264 to network element n is: Delay = tn' - tm' + Tm - Tn, where tn' and 265 tm' are the time when the traffic information of network element m 266 and network n reaches the centralized control node, and Tm and Tn are 267 transmission delay of the traffic information from network element m 268 and network element n to the centralized control node respectively 269 through delay deterministic network. 271 4. Procedures of the One-way Delay Measurement Method 273 In this section, the procedures of the proposed one-way delay 274 measurement method will be elaborated. Assume there are two network 275 element. It is determined that the time when the centralized control 276 node receives the first flow information is the first time, and the 277 time when the second flow information is received by the centralized 278 control node is determined to be the second time. The first flow 279 information is sent to the centralized control node via delay 280 deterministic network, and the second flow information is also sent 281 to the centralized control node via delay deterministic network. The 282 procedures of the one-way delay measurement method is shown in 283 Figure 2. 285 +-----------+ +-----------+ +---------------------+ +--------------+ 286 | Network | | Network | | Delay Deterministic | | Centralized | 287 | Element m | | Element n | | Network | | Control Node | 288 +-----+-----+ +-----+-----+ +---------------------+ +-------+------+ 289 | | | 290 | | | 291 | | | 292 | | The first transmission +-------+--------+ 293 | | delay is Tm | tm' represents | 294 +----------------------------------------------> the first time | 295 | | +-------+--------+ 296 | | | 297 | | | 298 | | The second transmission +-------+--------+ 299 | | delay is Tn | tn' represents | 300 | +-------------------------------> the second time| 301 | | +-------+--------+ 302 | | | 303 | | | 304 | | | 305 + + + 307 Figure 2: Figure 2: Procedures of the one-way delay measurement 308 method 310 The transmission delay of traffic from the first network element to 311 the second network element can be determined based on the first time, 312 the second time, the first transmission delay, and the second 313 transmission delay. 315 The first traffic information is sent by the first network element to 316 the centralized control node via a delay deterministic network at the 317 moment when the traffic passes through the first network element. 318 And the time when the traffic passes through the first network 319 element refers to the moment when traffic enters the first network 320 element or the time when traffic flows out of the first network 321 element. 323 The second traffic information is sent by the second network element 324 to the centralized control node via a delay deterministic network at 325 the moment when the traffic passes through the second network 326 element. And the time when the traffic passes through the second 327 network element refers to the moment when traffic enters the second 328 network element or the time when traffic flows out of the second 329 network element. 331 It is determined that the transmission delay of the first traffic 332 information from the first network element to the centralized control 333 node is the first transmission delay, and it is determined that the 334 transmission delay of the second traffic information from the second 335 network element to the centralized control node is the second 336 transmission delay. The transmission delay of traffic from the first 337 network element to the second network element can be determined based 338 on the following formula: Delay=tn'-tm'+Tm-Tn. Wherein, tn' 339 represents the second time, tm' represents the first time, Tm 340 represents the first transmission delay, Tn represents the second 341 transmission delay, and Delay represents transmission delay of the 342 traffic from the first network element to the second network element. 343 In the above method, the delay deterministic network is used to 344 ensure that the first transmission delay and the second transmission 345 delay are fixed delays. 347 5. Security Considerations 349 TBD. 351 6. IANA Considerations 353 TBD. 355 7. Normative References 357 [IEEE.1588.2008] 358 IEEE, "IEEE Standard for a Precision Clock Synchronization 359 Protocol for Networked Measurement and Control Systems", 360 July 2008. 362 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 363 Requirement Levels", BCP 14, RFC 2119, 364 DOI 10.17487/RFC2119, March 1997, 365 . 367 [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, 368 "Network Time Protocol Version 4: Protocol and Algorithms 369 Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, 370 . 372 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 373 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 374 May 2017, . 376 [RFC8186] Mirsky, G. and I. Meilik, "Support of the IEEE 1588 377 Timestamp Format in a Two-Way Active Measurement Protocol 378 (TWAMP)", RFC 8186, DOI 10.17487/RFC8186, June 2017, 379 . 381 [RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas, 382 "Deterministic Networking Architecture", RFC 8655, 383 DOI 10.17487/RFC8655, October 2019, 384 . 386 Authors' Addresses 388 Hongwei Yang 389 China Mobile 390 Beijing 391 100053 392 China 393 Email: yanghongwei@chinamobile.com 395 Peng Liu 396 China Mobile 397 Beijing 398 100053 399 China 400 Email: Liupengyjy@chinamobile.com