IEEE 802.1AS-2020：时间敏感网络同步标准

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"8021AS-2020.pdf" 本文将深入探讨IEEE 802.1AS-2020标准，该标准是针对时间敏感应用的局域网和城域网的定时与同步规范。由IEEE计算机学会的局域网/城域网标准委员会制定，此标准是对2011年版本的修订，旨在提供更精确和可靠的时钟同步技术，以支持时间敏感网络（TSN）的应用。 802.1AS标准的核心目标是在网络中实现高精度的时间同步，这对于许多实时通信和工业自动化系统至关重要。这些系统包括但不限于音频、视频流、工业自动化、汽车网络和物联网（IoT）设备。在这些应用中，数据必须在严格的时间窗口内传输，任何时钟偏差都可能导致服务质量下降甚至系统故障。标准802.1AS-2020引入了精确时间协议（Precision Time Protocol, PTP），这是一种用于网络设备间同步的协议。PTP允许网络中的设备通过共享一个准确的时间参考来同步它们的时钟，从而确保所有操作都在精确的时间点发生。它分为两个主要部分：Grandmaster（主时钟）和Slave（从时钟）。Grandmaster提供准确的时间源，而Slave设备则调整自己的时钟以匹配Grandmaster。标准中还涉及了网络层次结构的概念，即时钟层次，以确保在整个网络中实现稳定和一致的时间同步。在网络的不同层次上，时钟的精度逐层递减，但依然保持足够的精确度来满足应用需求。此外，标准还包括了故障检测和恢复机制，以确保即使在某些设备或链路故障的情况下，网络仍然能够维持其时间同步。 802.1AS-2020标准对TSN网络的贡献在于其提高了网络性能和可靠性。通过提供一致的时间参考，它可以确保数据包的精确传输，从而避免了延迟和抖动问题。这对于实时通信如音频和视频流至关重要，同时也为自动化系统提供了稳定的运行环境。在实际部署中，802.1AS与其他TSN标准（如802.1Qav、802.1Qcc等）结合使用，可以实现复杂的流量管理和优先级调度，确保关键数据包在其他非关键流量之前得到处理。这使得TSN网络能够满足严苛的实时性能要求，如在汽车行业的自动驾驶系统或工厂自动化生产线中。 IEEE 802.1AS-2020是TSN网络的基础，它定义了网络设备如何同步时间和管理时间敏感数据传输，从而为各种工业和通信应用提供可靠且高效的服务。随着TSN技术的不断发展和广泛应用，802.1AS标准将继续扮演着不可或缺的角色。

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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