IEEE 802.1AS-2011标准：时间同步在桥接局域网中的应用

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"8021AS-2011.pdf" 该标准，即IEEE 802.1AS，详细定义了在桥接和虚拟桥接的局域网（LAN）环境中，确保时间敏感应用（如音频和视频）的同步协议和流程。此标准由IEEE局域/城域网络标准委员会赞助，旨在为时间敏感应用提供可靠的时钟同步机制，以支持低延迟和高精度的时间关键通信。 802.1AS是AudioVideo Bridging (AVB)技术的一部分，AVB是一种在网络中传输音频和视频流的技术，它需要精确的时序同步来确保数据包在正确的时间到达接收端，从而避免音视频不同步。此外，802.1AS也与IEEE 1588 Precision Time Protocol (PTP) 相关，这是一种网络时钟同步协议，用于确保分布式系统中的设备具有高度一致的时钟。在802.1AS标准中，主要关注以下几个核心知识点： 1. **时间同步**：标准定义了一种方法，通过使用PTP来实现网络中的精确时间同步。PTP允许网络中的设备共享一个共同的时间参考，即使这些设备可能有微小的传输延迟。 2. **时间戳处理**：每个数据包在发送和接收时都会附带时间戳，这使得网络设备可以计算出传输延迟并进行补偿，从而提高实时性能。 3. **优先级和流量控制**：802.1AS与Time-Sensitive Networking (TSN)框架相结合，确保时间关键的数据包优先传输，不受非时间敏感流量的影响。这通过使用802.1Qbv（流量调度）和其他流量管理机制来实现。 4. **网络架构**：标准涵盖了如何在桥接网络中部署和配置同步机制，包括主时钟的选择、备份时钟策略以及时钟树的构建，以保证整个网络的稳定运行。 5. **兼容性和互操作性**：802.1AS设计的目标是与其他IEEE 802标准兼容，特别是802.1Q（VLAN）、802.1D（桥接）等，同时保证不同厂商的设备能够无缝协作。 6. **错误检测和恢复**：标准还包含了错误检测和恢复机制，例如，当主时钟失效时，网络能够自动切换到备用时钟，以保持同步服务的连续性。 IEEE 802.1AS标准对于实现高效、可靠和同步的音频、视频和其他时间敏感应用的网络传输至关重要。它不仅解决了传统网络中可能出现的同步问题，也为未来的物联网(IoT)和自动化系统中需要精确时间同步的应用奠定了基础。

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

notices and disclaimers appear in all publications containing this document and may be found under the

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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IEEE 802.1AS-2011标准：时间同步在桥接局域网中的应用

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