IEEE 802.1AS-2011：桥接LAN中时间敏感应用的定时与同步标准

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IEEE Std 802.1AS-2011，全称为《2011年IEEE标准：本地和城域网络——桥接局域网中时间敏感应用的定时与同步》，是由IEEE计算机学会的局域网/城域网标准委员会（LAN/MAN Standards Committee）制定的一份重要标准。这份标准专注于解决在桥接局域网（Bridged Local Area Networks, B-LANs）环境下，对于那些对时间有极高要求的应用程序，如工业自动化、远程医疗、金融交易等，提供精确的定时和同步服务。该标准主要关注的是时间敏感网络（Time-Sensitive Networking, TSN），它旨在通过增强网络的通信能力，确保在数据传输过程中，具有确定性的时间约束，这对于依赖于实时通信和低延迟的应用至关重要。在B-LAN环境中，由于网络的复杂性和动态性，确保时间一致性是一项挑战。IEEE 802.1AS-2011定义了一套规范，包括时间戳交换、时间同步协议以及服务质量（Quality of Service, QoS）机制，以实现网络中的同步和定时需求。标准规定了时间同步精度的要求，例如±1微秒或更小，这在许多应用场景中是必不可少的，比如电力系统中的电网控制、自动驾驶汽车的协调等。同时，它还涵盖了时间同步算法的设计，如PTP（Precision Time Protocol）的扩展和优化，以适应网络环境的变化和不同层次的时间同步需求。此外，IEEE 802.1AS-2011还强调了授权使用限制，指出文档的使用仅限于指定的机构（如重庆邮电大学），并指明了下载日期和来源，表明了知识产权的保护和合规使用的重要性。通过遵循此标准，网络设计者和管理员可以确保桥接局域网能够为那些对时间稳定性有极高依赖性的应用提供可靠的服务，从而提高整个系统的可靠性和安全性。在实施时，可能需要对现有网络架构进行改造，引入新的硬件和软件解决方案，以满足严格的定时和同步要求。 IEEE Std 802.1AS-2011是针对桥接局域网中时间敏感应用的必备技术指南，对于任何希望在高度实时性环境中运作的网络工程师和技术人员来说，理解和掌握这一标准是至关重要的。

Figure E.4—Propagation delay and residence time over a CSN Backbone................................................ 262

Figure E.5—CSN node-to-node path delay measurement........................................................................... 263

Figure E.6—IEEE 802.1AS Sync Message Propagation over the CSN backbone ..................................... 265

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List of tables

Table 6-1—Primitive data types .................................................................................................................... 15

Table 8-1—Illustration of formation of clockIdentity from EUI-48 ............................................................. 31

Table 8-2—Default values for priority1, for the respective media................................................................33

Table 8-3—timeSource enumeration............................................................................................................. 36

Table 10-1—Port role definitions .................................................................................................................. 68

Table 10-2—Destination address for Announce and Signaling messages .................................................... 86

Table 10-3—Ethertype for Announce and Signaling messages .................................................................... 86

Table 10-4—PTP message header................................................................................................................. 88

Table 10-5—Values for messageType field .................................................................................................. 88

Table 10-6—Values of flag bits..................................................................................................................... 89

Table 10-7—Announce message fields ......................................................................................................... 90

Table 10-8—Path trace TLV ......................................................................................................................... 91

Table 10-9—Signaling message fields .......................................................................................................... 92

Table 10-10—Message interval request TLV ............................................................................................... 93

Table 10-11—Interpretation of special values of linkDelayInterval ............................................................. 94

Table 10-12—Interpretation of special values of timeSyncInterval.............................................................. 94

Table 10-14—Definitions of bits of flags field of message interval request TLV ........................................ 95

Table 10-13—Interpretation of special values of announceInterval.............................................................. 95

Table 11-1—Destination address for Sync, Follow_Up, Pdelay_Req, Pdelay_Resp,

and Pdelay_Resp_Follow_Up messages ..............................................................................................123

Table 11-2—Ethertype for Sync, Follow_Up, Pdelay_Req, Pdelay_Resp, and

Pdelay_Resp_Follow_Up messages ..................................................................................................... 123

Table 11-4—Values of flag bits................................................................................................................... 125

Table 11-3—Values for messageType field ................................................................................................ 125

Table 11-6—References for sequenceId value exceptions.......................................................................... 126

Table 11-7—Value of control field ............................................................................................................. 126

Table 11-5—Value of correction field......................................................................................................... 126

Table 11-8—Sync message fields................................................................................................................ 127

Table 11-9—Follow_Up message fields ..................................................................................................... 127

Table 11-10—Follow_Up information TLV ............................................................................................... 128

Table 11-11—Pdelay_Req message fields .................................................................................................. 129

Table 11-12—Pdelay_Resp message fields................................................................................................. 130

Table 11-13—Pdelay_Resp_Follow_Up message fields ............................................................................ 130

Table 12-1—Parameters of MLME-TIMINGMSMT.request..................................................................... 139

Table 12-2—Parameters of MLME-TIMINGMSMST.confirm ................................................................ 140

Table 12-3—Parameters of MLME-TIMINGMSMT.indication ................................................................ 143

Table 12-4—Values of the Type field in the VendorSpecific information element.................................... 144

Table 13-1—TIMESYNC message fields ................................................................................................... 150

Table 14-1—Default Parameter Data Set Table .......................................................................................... 162

Table 14-2—Current Parameter Data Set Table.......................................................................................... 163

Table 14-3—Parent Parameter Data Set Table............................................................................................ 165

Table 14-4—Time Properties Parameter Data Set Table ............................................................................ 166

Table 14-5—portRole enumeration ............................................................................................................. 167

Table 14-6—Port Parameter Data Set Table ............................................................................................... 170

Table 14-7—Port Parameter Statistics Table.....................................................................................

.......... 173

Table 14-8—Acceptable Mas

er Table Parameter Data Set Table.............................................................. 174

Table 15-1—IEEE8021-AS MIB structure and object cross reference....................................................... 177

Table B.1—Wander generation TDEV requirement for LocalClock entity................................................ 246

Table B.2—ADEV limit corresponding to wander generation requirement of Table B.1.......................... 247

Table B.3—PTPDEV limit corresponding to wander generation requirement of Table B.1 ...................... 248

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IEEE Standard for

Local and metropolitan area networks—

Timing and Synchronization for

Time-Sensitive Applications in

Bridged Local Area Networks

IMPORTANT NOTICE: This standard is not intended to ensure safety, security, health, or

environmental protection. Implementers of the standard are responsible for determining appropriate

safety, security, environmental, and health practices or regulatory requirements.

This IEEE document is made available for use subject to important notices and legal disclaimers. These

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heading “Important Notice” or “Important Notices and Disclaimers Concerning IEEE Documents.”

They can also be obtained on request from IEEE or viewed at http://standards.ieee.org/IPR/

disclaimers.html.

1. Overview

1.1 Scope

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 local area network (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 Std 802.1D

-2004 and IEEE Std 802.1Q

-2005.

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.

1.2 Purpose

This standard enables stations attached to bridged LANs to meet the respective jitter, wander, and time

synchronization requirements for time-sensitive applications. This includes applications that involve

Information on references can be found in Clause 2.

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