IEEE 802.1AS-2020：时间敏感应用的本地和城域网定时与同步标准

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"802.1AS-2020是IEEE发布的一项关于本地和城域网络中时间敏感应用的时间同步标准。这个标准是802.1AS-2011的修订版，由IEEE计算机学会的局域网/城域网标准委员会开发和批准。" 802.1AS-2020协议详细说明了在局域网（LAN）和城域网（MAN）中如何实现精确的时间同步，这对于时间敏感的应用至关重要，例如音频、视频流媒体、工业自动化、电力系统和自动驾驶汽车等。这些应用需要在分布式系统之间保持极高的时间精度，以确保数据传输的准确性和实时性。该标准的核心目标是提供一种机制，使得网络设备能够获取和维持一个共同的时间参考，通常是以全球定位系统（GPS）或其他精密时间源为基础的。它定义了网络中的时钟同步协议和架构，包括时间戳的处理、时钟质量的评估以及同步错误的检测和恢复策略。 802.1AS-2020协议的主要组成部分包括： 1. **时间戳处理**：在数据包传输过程中，设备会附加上发送和接收的时间戳，以便在网络中进行时间校准。 2. **同步层**：定义了同步层的协议，包括主时钟的选举、时钟同步算法和时钟质量的维护。 3. **时间参考传递**：通过网络传递时间参考，确保所有设备都能与一个公共的时间源对齐。 4. **性能监测**：监控网络中的同步性能，包括时延、抖动和漂移，以便于调试和优化。 5. **故障恢复机制**：当时间源或同步路径出现故障时，协议应能快速恢复同步状态，以保证服务的连续性。 802.1AS-2020相对于2011版本的修订可能涉及了技术改进、性能提升、兼容性增强以及对新应用需求的支持。这些修订可能包括更高效的时间同步算法、更严格的时间精度要求或者对新兴技术如5G网络和物联网(IoT)的适应性增强。 802.1AS-2020是现代网络基础设施中不可或缺的一部分，它确保了依赖时间同步的各种应用能够可靠、准确地运行。对于设计、实施和维护这些网络的工程师来说，理解并应用这个标准至关重要。

List of tables

Table 6-1—Primitive data types ................................................................................................................... 31

Table 8-1—Default values for priority1, for the respective media............................................................... 55

Table 8-2—TimeSource enumeration .......................................................................................................... 57

Table 10-1—Summary of scope of global variables used by time synchronization state machines 

(see 10.2.4 and 10.2.5).................................................................................................................................. 76

Table 10-2—PTP Port state definitions ........................................................................................................ 98

Table 10-3—Summary of scope of global variables used by best master clock selection, external port

configuration, and announce interval setting state machines (see 10.3.9 and 10.3.10) .............................. 107

Table 10-4—Destination address for Announce and Signaling messages ................................................. 142

Table 10-5—EtherType for Announce and Signaling messages................................................................ 142

Table 10-6—Propagate TLVs of IEEE Std 1588-2019 .............................................................................. 144

Table 10-7—PTP message header.............................................................................................................. 144

Table 10-8—Values for messageType field ............................................................................................... 145

Table 10-9—Values of flag bits.................................................................................................................. 146

Table 10-10—messageTypeSpecific semantics ......................................................................................... 147

Table 10-11—Announce message fields .................................................................................................... 148

Table 10-12—Path trace TLV .................................................................................................................... 149

Table 10-13—Signaling message fields ..................................................................................................... 150

Table 10-14—Message interval request TLV ............................................................................................ 151

Table 10-15—Interpretation of special values of logLinkDelayInterval.................................................... 152

Table 10-16—Interpretation of special values of logTimeSyncInterval .................................................... 152

Table 10-17—Interpretation of special values of logAnnounceInterval .................................................... 153

Table 10-18—Definitions of bits of flags field of message interval request TLV ..................................... 153

Table 10-19—gPTP-capable TLV.............................................................................................................. 154

Table 10-20—gPTP-capable message interval request TLV...................................................................... 155

Table 10-21—Interpretation of special values of logGptpCapableMessageInterval.................................. 156

Table 11-1—Value of meanLinkDelayThresh for various links ................................................................ 169

Table 11-2 —Summary of scope of global variables used by 

time synchronization state machines (see 10.2.4 and 10.2.5)..................................................................... 171

Table 11-3—Destination address for Sync, Follow_Up, Pdelay_Req, Pdelay_Resp, and

Pdelay_Resp_Follow_Up messages ........................................................................................................... 196

Table 11-4—EtherType for Sync, Follow_Up, Pdelay_Req, Pdelay_Resp, and 

Pdelay_Resp_Follow_Up messages ........................................................................................................... 196

Table 11-5—Values for messageType field ............................................................................................... 198

Table 11-6—Value of correctionField........................................................................................................ 199

Table 11-7—References for sequenceId value exceptions......................................................................... 199

Table 11-8—Sync message fields if twoStep flag is TRUE....................................................................... 200

Table 11-9—Sync message fields if twoStep flag is FALSE ..................................................................... 200

Table 11-10—Follow_Up message fields .................................................................................................. 201

Table 11-11—Follow_Up information TLV .............................................................................................. 202

Table 11-12—Pdelay_Req message fields ................................................................................................. 203

Table 11-13—Pdelay_Resp message fields.........................................................................................

....... 204

Table 11-14—Pdelay_Resp_Follow_Up message fields ........................................................................... 204

Table 12-1—Values of bits of tmFtmSupport ............................................................................................ 214

Table 12-2—FTM parameters relevant to time-synchronization transport ................................................ 227

Table 12-3—Values of Burst Duration and Min Delta FTM, for each value of currentLogSyncInterval . 228

Table 12-4—Values of the Type field in the VendorSpecific information element................................... 228

Table 13-1—TIMESYNC message fields .................................................................................................. 235

Table 14-1—defaultDS table ...................................................................................................................... 251

Table 14-2—currentDS table...................................................................................................................... 253

Table 14-3—parentDS table ....................................................................................................................... 255

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Table 14-4—timePropertiesDS table.......................................................................................................... 256

Table 14-5—pathTraceDS table ................................................................................................................. 257

Table 14-6—acceptableMasterTableDS table ............................................................................................ 258

Table 14-7—portState enumeration............................................................................................................ 258

Table 14-8—delayMechanism enumeration............................................................................................... 259

Table 14-9—Description of pdelayTruncatedTimestampsArray ............................................................... 266

Table 14-10—portDS table......................................................................................................................... 267

Table 14-11—descriptionPortDS table....................................................................................................... 269

Table 14-12—portStatisticsDS table .......................................................................................................... 272

Table 14-13—acceptableMasterPortDS table ............................................................................................ 273

Table 14-14—externalPortConfigurationPortDS table .............................................................................. 274

Table 14-15—asymmetryMeasurementModeDS table .............................................................................. 274

Table 14-16—commonServicesPortDS table ............................................................................................. 275

Table 14-17—cmldsDefaultDS table.......................................................................................................... 276

Table 14-18—cmldsLinkPortDS table ....................................................................................................... 280

Table 14-19—cmldsLinkPortStatisticsDS table ......................................................................................... 282

Table 14-20—cmldsAsymmetryMeasurementModeDS table.................................................................... 283

Table 15-1—IEEE8021-AS-V2 MIB structure and object cross reference................................................ 285

Table 16-1—CSN TLV .............................................................................................................................. 375

Table 16-2—Definitions and option selections per link technology .......................................................... 377

Table B-1—Wander generation TDEV requirement for LocalClock entity .............................................. 399

Table B-2—ADEV limit corresponding to wander generation requirement of Table B-1 ........................ 400

Table B-3—PTPDEV limit corresponding to wander generation requirement of Table B-1 .................... 401

Table B-4—Maximum endpoint filter bandwidths needed to meet respective MTIE masks and 

peak-to-peak jitter limits............................................................................................................................. 403

Table B-5—Breakpoints for Mask 1 .......................................................................................................... 404

Table B-6—Breakpoints for Mask 2 .......................................................................................................... 404

Table C-1—Timescale parameters ............................................................................................................. 405

Table C-2—Timescale conversions............................................................................................................ 408

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IEEE Std 802.1AS-2020

IEEE Standard for Local and Metropolitan Area Networks

Timing and Synchronization for Time-Sensitive Applications

2. Normative references

The following referenced documents are indispensable for the application of this standard (i.e., they must be

understood and used; therefore, each referenced document is cited in text, and its relationship to this

document is explained). For dated references, only the edition cited applies. For undated references, the

latest edition of the referenced document (including any amendments or corrigenda) applies.

IEEE Std 754™-2008, IEEE Standard for Floating-Point Arithmetic.

2, 3

IEEE Std 802®-2014, IEEE Standard for Local and Metropolitan Area Networks—Overview and

Architecture.

IEEE Std 802c™-2017, IEEE Standard for Local and Metropolitan Area Networks—Overview and

Architecture—Amendment 2: Local Medium Access Control (MAC) Address Usage.

IEEE Std 802.1AC™-2016, IEEE Standard for Local and metropolitan area networks—Media Access

Control (MAC) Service Definition.

IEEE Std 802.1AX™-2014, IEEE Standard for Local and metropolitan area networks—Link Aggregation.

IEEE Std 802.1Q™-2018, IEEE Standard for Local and Metropolitan Area Networks—Bridges and Bridged

Networks.

IEEE Std 802.3™-2018, IEEE Standard for Ethernet.

IEEE Std 802.11™-2016, IEEE Standard for Information technology—Telecommunications and

information exchange between systems—Local and metropolitan area networks—Specific requirements,

Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.

IEEE Std 1588™-2019, IEEE Standard for a Precision Clock Synchronization Protocol for Networked

Measurement and Control Systems.

IERS Bulletin C (see https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html).

IETF RFC 2863 (June 2000), The Interfaces Group MIB, K. McCloghrie and F. Kastenholz.

IETF RFC 3410 (Dec. 2002), Introduction and Applicability Statements for Internet Standard Management

Framework, J. Case, R. Mundy, D. Partain, and B. Stewart.

IETF RFC 3418 (Dec. 2002), Management Information Base (MIB) for the Simple Network Management

Protocol (SNMP), R. Presuhn, ed.

ISO 80000-3:2006, Quantities and units — Part 3: Space and time.

IEEE publications are available from The Institute of Electrical and Electronics Engineers (https://standards.ieee.org).

The IEEE standards or products referenced in this clause are trademarks owned by The Institute of Electrical and Electronics

Engineers, Incorporated.

IETF Requests for Comments (RFCs) are available from the Internet Engineering Task Force (https://www.rfc-editor.org).

ISO publications are available from the International Organization for Standardization (https://www.iso.org) and the American

National Standards Institute (https://www.ansi.org).

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