IEEE 802.1AS-2020: 时间敏感网络同步标准

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"IEEE 802.1AS-2020.pdf 是一份由IEEE Computer Society制定的局域网和城域网标准，专门针对时间敏感应用的时钟同步技术。该标准是2011年版本的修订版，旨在为时间同步应用程序提供精确的定时和同步解决方案。" IEEE 802.1AS，也称为通用精确时间协议（gPTP），是用于网络设备之间同步时间的一种协议。这个协议尤其适用于那些对时间精度有严格要求的应用，如音频、视频、工业自动化以及通信网络等领域。它定义了一种机制，通过这种机制，网络中的设备能够共享一个准确的时间参考，从而确保所有操作在同一时间点进行。该标准的主要特点包括： 1. **时间戳处理**：gPTP协议利用时间戳技术来记录数据包在网络中传输的时间，以便精确计算传输延迟并进行校正。 2. **层次化时钟模型**：gPTP将网络中的时钟分为不同的等级，主时钟向从时钟发送时间信息，从时钟根据接收到的信息调整自身时钟，以实现整个网络的时间同步。 3. **多路径传输**：支持多个路径传输时间信息，增强了网络的可靠性和容错能力，即使某个路径出现故障，也能保证时间同步不中断。 4. **优先级和选举机制**：gPTP定义了选举主时钟的规则，基于设备的优先级和网络路径质量来确定。 5. **边界时钟和透明时钟**：两种类型的时钟在gPTP中扮演不同角色，边界时钟负责在gPTP域与其他网络之间转换时间信息，而透明时钟则在域内转发时间戳。 6. **性能监控和诊断**：提供了工具来监控和诊断网络中的时间同步性能，帮助识别并解决问题。 7. **兼容性与扩展性**：IEEE 802.1AS标准兼容其他时间同步协议，如IEEE 1588 PTP，并且设计上允许未来的技术扩展和升级。 8. **安全性考虑**：标准还包含了对网络安全性的考量，确保时间同步信息不被篡改或干扰。通过这些特性，IEEE 802.1AS-2020为需要高精度时间同步的网络环境提供了强大的支撑，有助于提升系统的稳定性和效率。对于那些依赖时间同步的复杂应用，如5G通信、数据中心互操作性、物联网(IoT)以及自动化控制等，该标准起着至关重要的作用。

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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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