IEEE 802.1AS: 时钟同步在时间敏感局域网中的应用

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"IEEE 802.1AS-d6-1是关于时间敏感应用在桥接局域网中的定时和同步标准草案" IEEE 802.1AS标准是 IEEE 802 工作组制定的一个关键协议，用于解决在桥接局域网络（LAN）中时间敏感应用的时间同步问题。这个标准对于需要精确时间同步的网络服务，如音频、视频流传输、工业自动化和物联网(IoT)设备等至关重要。在时间敏感应用中，网络设备必须能够准确地共享时间信息，以便确保数据包在正确的时间发送和接收。802.1AS 提供了一种框架，使得网络中的所有设备能够达到微秒甚至纳秒级别的精度，这对于实时通信和高精度操作至关重要。标准草案802.1AS-d6-1是该标准的未批准版本，意味着它仍然在开发和审查过程中，可能会有进一步的修改。尽管如此，这个草案已经被授权给IEEE标准委员会的参与者用于标准化活动。但是，未经IEEE标准许可，不得将此文档用于任何符合性或合规性目的，也不得将其提交给其他标准开发组织进行标准化活动。 IEEE标准的版权和权限管理非常严格。除了IEEE标准委员会的参与者外，其他实体如果想要复制或部分复制此文档，必须首先获得IEEE标准许可和合同经理的批准。这确保了标准开发过程的透明度和一致性，同时也保护了知识产权。 802.1AS标准通常会涵盖以下核心概念和技术： 1. **时间戳**：在网络设备之间传输的数据包携带时间戳，以便接收方可以精确地确定数据的生成时间。 2. **时间同步协议**：例如，通用精确时间协议(GPTP)或精确时间协议(PTP)，这些协议允许网络设备通过网络共享时间信息。 3. **层次化时钟模型**：网络中的设备被组织成层次结构，主时钟提供参考时间，子时钟根据主时钟进行同步。 4. **同步机制**：包括边界时钟和透明时钟，前者处理进入和离开网络的数据包的时间戳，后者则在不修改数据包的情况下传递时间信息。 5. **性能指标**：定义了网络设备在时间同步方面的性能要求，如同步精度、延迟和抖动等。 6. **网络设计考虑**：如何在复杂的网络环境中实现高效的时间同步，包括路径选择、带宽管理和故障恢复策略。这个标准对于构建高效、可靠和低延迟的网络环境至关重要，特别是对于那些对时间同步要求极高的应用，如专业音频视频系统、电力自动化、自动驾驶汽车通信等。随着技术的发展，802.1AS将继续进化以满足不断增长的对时间敏感应用的需求。

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This is an unapproved IEEE Standards Draft, subject to change.

Introduction to IEEE Std 802.1AS™

(This introduction is not part of P802.1AS, IEEE Standard for Local and metropolitan area networks— Timing and Syn-

chronization for Time-Sensitive Applications in Bridged Local Area Networks.)

This standard specifies the protocol and procedures used to ensure that the synchronization requirements are

met for time sensitive applications, such as audio and video, across Bridged and Virtual Bridged Local Area

Networks consisting of LAN media where the transmission delays are fixed and symmetrical; for example,

IEEE 802.3 full duplex links. This includes the maintenance of synchronized time during normal operation

and following addition, removal, or failure of network components and network reconfiguration. It specifies

the use of IEEE 1588 specifications where applicable in the context of IEEE Stds 802.1D and 802.1Q.

Synchronization to an externally provided timing signal (e.g., a recognized timing standard such as UTC or

TAI) is not part of this standard but is not precluded.

This is the first edition of IEEE Std 802.1AS.

This standard contains state-of-the-art material. The area covered by this standard is undergoing evolution.

Revisions are anticipated within the next few years to clarify existing material, to correct possible errors, and

to incorporate new related material. Information on the current revision state of this and other IEEE 802

standards may be obtained from

Secretary, IEEE-SA Standards Board

445 Hoes Lane

P.O. Box 1331

Piscataway, NJ 08855-1331

USA

<<The following Editor’s Note was copied from Draft IEEE 802.1AR/D0.1.>>

<<The “Introduction to IEEE Std xxx” clause found in the front matter for all IEEE 802.1 standards is not

really an introduction to the standard per se, but really exists so that the revision history of the current

standard and its relationship to prior editions, together with its relationship to (revisions of) companion

standards can be easiy grasped. For a first edition this text is necessarily brief, and is mainly a repetition of

the current scope together with a note that it is indeed the first edition.>>

Timing and Synchronization for Time-Sensitive Applications in Bridged Local Area Networks P802.1AS/D6.1

August 3, 2009

This is an unapproved IEEE Standards Draft, subject to change.

Contents

Editors’ Foreword...................................................................................................................................... 3

1. Overview.................................................................................................................................................. 25

1.1 Scope...................................................................................................................................... 25

1.2 Purpose................................................................................................................................... 25

2. References................................................................................................................................................ 26

3. Definitions ............................................................................................................................................... 27

4. Abbreviations........................................................................................................................................... 29

5. Conformance............................................................................................................................................ 32

5.1 Requirements terminology.....................................................................................................32

5.2 Protocol Implementation Conformance Statement (PICS).................................................... 32

5.3 Timing-aware Bridge and End-point requirements ............................................................... 32

5.4 MAC-specific timing and synchronization Methods for IEEE Std 802.3 Full-Duplex Links ..

5.5 MAC-specific timing and synchronization Methods for IEEE Std 802.11........................... 33

5.6 MAC-specific timing and synchronization Methods for IEEE Std 802.3 EPON.................. 34

6. Conventions ............................................................................................................................................. 35

6.1 General................................................................................................................................... 35

6.2 Service specification method and notation ............................................................................ 35

6.3 Data types and on-the-wire formats in an 802.1AS network................................................. 35

7. Clock synchronization model for a bridged local area network (Informative)........................................ 39

8. Characterization of IEEE 1588 Precision Time Protocol entities and IEEE 802.11v entities used in IEEE

802.1AS41

8.1 802.1AS domain .................................................................................................................... 41

8.2 Timescale............................................................................................................................... 41

8.3 Communication path asymmetry........................................................................................... 42

8.4 Messages................................................................................................................................ 43

8.5 Ports ....................................................................................................................................... 44

8.6 Time-aware system characterization ..................................................................................... 46

9. Application interfaces.............................................................................................................................. 51

9.1 Overview of the interfaces..................................................................................................... 51

9.2 ClockSource interface............................................................................................................ 52

9.3 ClockTargetEventCapture interface ...................................................................................... 52

9.4 ClockTargetTriggerGenerate interface.................................................................................. 53

9.5 ClockTargetClockGenerator interface................................................................................... 54

9.6 ClockTargetPhaseDiscontinuity interface ............................................................................. 55

10. Media-independent layer specification.................................................................................................... 57

10.1 Overview................................................................................................................................ 57

10.2 Time synchronization state machines.................................................................................... 59

10.3 Best master clock selection and announce interval setting state machines ........................... 81

P802.1AS/D6.1 LOCAL AND METROPOLITAN AREA NETWORKS

August 3, 2009

This is an unapproved IEEE Standards Draft, subject to change.

10.4 Message attributes................................................................................................................ 102

10.5 Message formats .................................................................................................................. 103

10.6 Protocol timing characterization.......................................................................................... 112

11. Media-dependent layer specification for full-duplex, point-to-point links............................................ 115

11.1 Overview.............................................................................................................................. 115

11.2 State machines for MD entity specific to full-duplex, point-to-point links......................... 121

11.3 PTP Message attributes........................................................................................................ 140

11.4 Message formats .................................................................................................................. 142

11.5 Protocol timing characterization.......................................................................................... 149

12. Media-dependent layer specification for IEEE 802.11 links................................................................. 152

12.1 Overview.............................................................................................................................. 152

12.2 Messages.............................................................................................................................. 154

12.3 Determination of asCapable................................................................................................. 154

12.4 Media Dependent master state machine .............................................................................. 154

12.5 Media Dependent slave state machine................................................................................. 158

12.6 Format of VendorSpecific field ........................................................................................... 161

12.7 Message interval requests .................................................................................................... 162

13. Media-dependent layer specification for interface to IEEE 802.3 Ethernet passive optical network

(EPON) link163

13.1 Overview.............................................................................................................................. 163

13.2 Message attributes................................................................................................................ 165

13.3 Message format.................................................................................................................... 165

13.4 Layering for IEEE 802.3 EPON links ................................................................................. 168

13.5 Service interface definitions ................................................................................................ 168

13.6 MD entity global variables ..................................................................................................170

13.7 State machines ..................................................................................................................... 170

13.8 Message transmission intervals ........................................................................................... 173

14. Clock data sets ....................................................................................................................................... 175

14.1 General specifications for data set members ....................................................................... 175

14.2 Data sets for ordinary and 802.1AS boundary clocks ......................................................... 178

14.3 Data sets for transparent clocks ........................................................................................... 185

15. Managed object definitions.................................................................................................................... 189

15.1 oDefaultDS managed object class ....................................................................................... 189

15.2 oCurrentDS managed object class....................................................................................... 191

15.3 oParentDS managed object class ......................................................................................... 192

15.4 oTimePropertiesDS managed object class........................................................................... 194

15.5 oPortDS managed object class............................................................................................. 197

Annex A (normative)PICS proforma........................................................................................................... 201

A.1 Introduction.......................................................................................................................... 201

A.2 Abbreviations and special symbols...................................................................................... 201

A.3 Instructions for completing the PICS proforma................................................................... 202

A.4 PICS proforma for IEEE P802.1AS/D6.1 ........................................................................... 203

A.5 Major capabilities ................................................................................................................ 205

A.6 Media access control methods............................................................................................. 206

A.7 Minimal time aware system................................................................................................. 206

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IEEE 802.1AS: 时钟同步在时间敏感局域网中的应用

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