ISO/IEC/IEEE 8802-1AS:2021/Amd 3:2026

International
Standard
ISO/IEC/IEEE
8802-1AS
Second edition
Information technology —
2021-11
Telecommunications and
information exchange between
AMENDMENT 3
systems — Local and metropolitan
2026-08
area networks —
Part 1AS:
Timing and synchronization for
time-sensitive applications in
bridged local area networks
AMENDMENT 3: Hot standby and
clock drift error reduction
Technologies de l'information — Télécommunications et
échange d'information entre systèmes — Réseaux locaux et
métropolitains —
Partie 1AS: Temporisation et synchronisation pour les
applications sensibles au temps des réseaux locaux pontés
AMENDEMENT 3: Secours immédiat et réduction d'erreur de
dérive d'horloge
Reference number
ISO/IEC/IEEE 8802-1AS:2021/
Amd.3:2026(en)
© IEEE 2024
ISO/IEC/IEEE 8802-1AS:2021/Amd.3:2026(en)
© IEEE 2024
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ii
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iii
Title page
IEEE Std 802.1ASdm™-2024
(Amendment to IEEE Std 802.1AS™-2020
as amended by IEEE Std 802.1AS™-2020/Cor 1-2021,
IEEE Std 802.1ASdr™-2024,
and IEEE Std 802.1ASdn™-2024)
IEEE Standard for
Local and Metropolitan Area Networks—
Timing and Synchronization for
Time-Sensitive Applications
Amendment 3: Hot Standby and Clock
Drift Error Reduction
Developed by the
LAN/MAN Standards Committee
of the
IEEE Computer Society
Approved 26 September 2024
IEEE SA Standards Board
Abstract: This amendment to IEEE Std 802.1AS™-2020 specifies hot standby and addresses
errors and omissions in the description of existing functionality.
Keywords: amendment, best timeTransmitter, frequency offset, Grandmaster Clock, Grandmaster
PTP Instance, hot standby, IEEE 802.1AS™, IEEE 802.1ASdm™, phase offset, PTP End Instance,
PTP Relay Instance, synchronization, syntonization, time-aware system
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PDF: ISBN 979-8-8557-1240-7 STD27316
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Participants
At the time this standard was submitted to the IEEE SA Standards Board for approval, the IEEE 802.1
Working Group had the following membership:
Glenn Parsons, Chair
Jessy V. Rouyer, Vice Chair
János Farkas, TSN Task Group Chair
Geoffrey Garner, Editor
Katsuyuki Akizuki Yoshihiro Ito Atsushi Sato
Venkat Arunarthi Michael Karl
Frank Schewe
Ralf Assmann Stephan Kehrer
Michael Seaman
Rudy Belliardi Marcel Kiessling
Maik Seewald
Christian Boiger Gavin Lai
Ramesh Sivakolundu
Paul Bottorff Yunping (Lily) Lyu
Johannes Specht
Radhakrishna Canchi Christophe Mangin
Nemanja Stamenic
Feng Chen Scott Mansfield
Marius Stanica
Abhijit Choudhury Olaf Mater
Guenter Steindl
Anna Engelmann David McCall
Karim Traore
Donald Fedyk Martin Mittelberger
Max Turner
Norman Finn Hiroki Nakano
Balazs Varga
Craig Gunther Takumi Nomura
Ganesh Venkatesan
Stephen Haddock Donald R. Pannell
Leon Wessels
Mark Hantel Dieter Proell
Ludwig Winkel
Marc Holness
Karen Randall
Jordon Woods
Daniel Hopf Maximilian Riegel
Takahiro Yamaura
Woojung Huh Silvana Rodrigues
Satoko Itaya Rajeev Roy Nader Zein
The following members of the individual balloting committee voted on this standard. Balloters may have
voted for approval, disapproval, or abstention.
Thomas Alexander Lokesh Kabra Dieter Proell
Piotr Karocki
Boon Chong Ang Denis Reilly
Butch Anton Stephan Kehrer
Maximilian Riegel
Douglas Arnold Stuart Kerry
Silvana Rodrigues
Stefan Aust Yongbum Kim
Benjamin Rolfe
Denis Beaudoin Jeff Koftinoff
Zoltan Roman
Gavin Lai
Christian Boiger
Jessy V. Rouyer
Vern Brethour Hyeong Ho Lee
Reinhard Schrage
Juan Carreon Joseph Levy
Jhony Sembiring
Pin Chang Greg Luri
Johannes Specht
David Chen Jingfei Lv
Guenter Steindl
Christophe Mangin
Rodney Cummings
Walter Struppler
János Farkas William-Rogelio Marchand-Niño
David Tepen
Donald Fedyk Brett McClellan
Richard Tse
Avraham Freedman Jonathon McLendon
Max Turner
Geoffrey Garner Martin Mittelberger
Ganesh Venkatesan
Craig Gunther Ronald Murias
John Vergis
Marco Hernandez Rajesh Murthy
Xiaohui Wang
Werner Hoelzl Mfanasibili Nkonyane
Stephen Webb
Oliver Holland Satoshi Obara
Karl Weber
Tetsushi Ikegami Glenn Parsons
Scott Willy
Yoshihiro Ito Bansi Patel
Ludwig Winkel
Abdul Jabbar Arumugam Paventhan
Andreas Wolf
Raj Jain Cam Posani
SangKwon Jeong Clinton Powell Oren Yuen
Pranav Jha Venkatesha Prasad Qiyue Zou
When the IEEE SA Standards Board approved this standard on 26 September 2024, it had the following
membership:
David J. Law, Chair
Jon W. Rosdahl, Vice Chair
Gary Hoffman, Past Chair
Alpesh Shah, Secretary
Sara R. Biyabani Hao Hu Hiroshi Mano
Paul Nikolich
Ted Burse Yousef Kimiagar
Robby Robson
Stephen Dukes Joseph L. Koepfinger*
Lei Wang
Doug Edwards Howard Li
F. Keith Waters
J. Travis Griffith Xiaohui Liu
Sha Wei
Guido R. Hiertz John Haiying Lu
Philip B. Winston
Ronald W. Hotchkiss Kevin W. Lu
Don Wright
*Member Emeritus
Introduction
This introduction is not part of IEEE Std 802.1ASdm-2024, IEEE Standard for Local and Metropolitan Area
Networks—Timing and Synchronization for Time-Sensitive Applications—Amendment 3: Hot Standby and Clock
Drift Error Reduction.
The first edition of IEEE Std 802.1AS was published in 2011. A first corrigendum, IEEE Std
802.1AS™-2011/Cor 1-2013, provided technical and editorial corrections. A second corrigendum, IEEE St d
802.1AS™-2011/Cor 2-2015 provided additional technical and editorial corrections.
The second edition, IEEE Std 802.1AS-2020, added support for multiple gPTP domains, Common Mean
Link Delay Service, external port configuration, and Fine Timing Measurement for 802.11 transport.
Backward compatibility with IEEE Std 802.1AS-2011 was maintained. A corrigendum, IEEE Std
802.1AS-2020/Cor 1-2021, provides technical and editorial corrections.
This amendment to IEEE Std 802.1AS-2020 specifies hot standby and addresses errors and omissions in the
description of existing functionality. Hot standby guards against the failure of a single Grandmaster PTP
Instance or the failure of communication from that Grandmaster PTP Instance to a Clock Target.
Contents
3. Definitions . 16
4. Acronyms and abbreviations . 17
5. Conformance. 18
5.4 PTP Instance requirements and options. 18
5.5 MAC-specific timing and synchronization methods for full-duplex IEEE 802.3 links . 20
7. Time-synchronization model for a packet network . 22
7.2 Architecture of a time-aware network . 22
7.4 PTP Instance architecture . 28
8. IEEE 802.1AS concepts and terminology . 30
8.1 gPTP domain. 30
8.5 Ports . 31
9. Application interfaces . 32
9.2 ClockSourceTime interface .32
9.3 ClockTargetEventCapture interface . 32
9.4 ClockTargetTriggerGenerate interface . 33
9.5 ClockTargetClockGenerator interface. 34
9.6 ClockTargetPhaseDiscontinuity interface . 35
10. Media-independent layer specification. 37
10.2 Time-synchronization state machines. 37
10.3 Best timeTransmitter clock selection, external port configuration, and announce
interval setting state machines . 49
10.4 State machines related to signaling gPTP capability . 71
10.5 Message attributes. 76
10.6 Message formats . 76
10.7 Protocol timing characterization. 79
11. Media-dependent layer specification for full-duplex point-to-point links. 81
11.1 Overview. 81
11.2 State machines for MD entity specific to full-duplex point-to-point links. 82
11.3 Message attributes. 104
11.4 Message formats . 105
11.5 Protocol timing characterization. 108
11.6 Control of computation of neighborRateRatio . 110
13. Media-dependent layer specification for interface to IEEE 802.3 Ethernet passive optical
network link . 111
13.3 Message format. 111
14. Timing and synchronization management. 112
14.1 General. 112
14.2 Default Parameter Data Set (defaultDS). 115
14.3 Current Parameter Data Set (currentDS) . 115
14.4 Parent Parameter Data Set (parentDS). 115
14.7a PTP Instance Synchronization Parameter Data Set (ptpInstanceSyncDS). 116
14.7b Drift Tracking Parameter Data Set (driftTrackingDS) . 117
14.8 Port Parameter Data Set (portDS). 118
14.10 Port Parameter Statistics Data Set (portStatisticsDS). 120
14.13 Asymmetry Measurement Mode Parameter Data Set (asymmetryMeasurementModeDS) 121
14.16 Common Mean Link Delay Service Link Port Parameter Data Set (cmldsLinkPortDS). 122
14.17 Common Mean Link Delay Service Link Port Parameter Statistics Data Set
(cmldsLinkPortStatisticsDS) . 123
14.19 Hot Standby System Parameter Data Set (hotStandbySystemDS). 123
14.20 Hot Standby System Description Parameter Data Set (hotStandbySystemDescriptionDS) 125
16. Media-dependent layer specification for CSN. 126
16.4 Path delay measurement over a CSN backbone . 126
16.5 Synchronization messages .126
17. YANG data model . 127
17.1 YANG framework . 127
17.2 IEEE 802.1AS YANG data model . 127
17.3 Structure of the YANG data model . 132
17.5 YANG schema tree definitions. 132
17.6 YANG modules . 133
18. Hot standby . 141
18.1 General. 141
18.2 Overview. 141
18.3 PTP Instance configuration. 142
18.4 PtpInstanceSyncStatus state machine . 142
18.5 HotStandbySystem state machine. 146
18.6 PrimarySecondaryOffset state machine. 151
Annex A (normative) Protocol Implementation Conformance Statement (PICS) proforma . 153
A.5 Major capabilities . 153
A.7 Minimal time-aware system. 154
A.8 Signaling . 155
A.9 Best timeTransmitter clock.155
A.10 Grandmaster-capable PTP Instance . 156
A.11 Media-independent timeTransmitter. 156
A.13 Media-dependent, full-duplex point-to-point link . 156
A.19 Remote management. 157
Annex B (normative) Performance requirements. 158
B.2 PTP Instance requirements . 158
Annex F (informative) PTP profile included in this standard . 159
F.3 PTP attribute values . 159
Annex G (informative) The asymmetry compensation measurement procedure based on line-swapping . 160
G.3 Measurement procedure.160
Annex H (informative) Bibliography . 162
List of Figures
Figure 7-3—Time-aware network example for multiple gPTP domains . 23
Figure 7-4—Time-aware network example for synchronization path redundancy, with one clock
source providing time to two domains. 25
Figure 7-5—Time-aware network example for GM redundancy with one primary GM and one
secondary GM, which are separated in two gPTP domains . 26
Figure 7-6—Time-aware network example for hot standby with both GM and partial path
redundancy. 27
Figure 7-8—Model for a PTP Instance and its interfaces to higher-layer applicationsmodel. 29
Figure 10-2—Time-synchronization state machines—overview and interrelationships. 38
Figure 10-6—ClockTimeTransmitterSyncOffset state machine . 47
Figure 10-9—ClockTimeReceiverSync state machine. 49
Figure 10-12—External port configuration state machines—overview and interrelationships . 50
Figure 10-16—PortAnnounceInformationExt state machine . 62
Figure 10-17—PortStateSettingExt state machine . 65
Figure 10-18—PortAnnounceTransmit state machine . 66
Figure 10-19—AnnounceIntervalSetting state machine. 68
Figure 10-20—SyncIntervalSetting state machine . 70
Figure 10-21—GptpCapableTransmit state machine . 72
Figure 10-22—GptpCapableReceive state machine. 73
Figure 10-23—GptpCapableIntervalSetting state machine. 75
Figure 11-4—Detail of MD entity time-synchronization state machines for full-duplex point-to-point
links. 83
Figure 11-5—Peer-to-peer delay mechanism state machines—overview and interrelationships . 84
Figure 11-6—MDSyncReceiveSM state machine. 91
Figure 11-7—MDSyncSendSM state machine. 94
Figure 11-9—MDPdelayReq state machine . 101
Figure 17-1—Overview of YANG tree . 128
Figure 17-2—PTP Instance detail. 129
Figure 17-3—PTP Port detail . 130
Figure 17-4—Common services detail . 131
Figure 18-1—Model for hot standby entity in a time-aware system, and its interfaces to
higher-layer applications. 141
Figure 18-2—PtpInstanceSyncStatus state machine . 145
Figure 18-3—HotStandbySystem state machine. 151
Figure 18-4—PrimarySecondaryOffset state machine . 152
Figure G-1—Asymmetry compensation measurement procedure . 160
List of Tables
Table 10-1—Summary of scope of global variables used by time synchronization state machines
(see 10.2.4 and 10.2.5). 41
Table 10-3—Summary of scope of global variables used by best timeTransmitter clock selection,
external port configuration, and announce interval setting state machines (see 10.3.9
and 10.3.10) . 51
Table 10-9—Values of flag bits. 77
Table 10-10—messageTypeSpecific semantics . 78
Table 10-13—Signaling message fields . 78
Table 11-1—Value of meanLinkDelayThresh for various links . 85
Table 11-2—Summary of scope of global variables used by time synchronization state machines
(see 10.2.4 and 10.2.5). 86
Table 11-6—Value of correctionField. 105
Table 11-10—Follow_Up message fields . 106
Table 11-8—Sync message fields if twoStep flag is TRUE. 106
Table 11-9—Sync message fields if twoStep flag is FALSE. 106
Table 11-11a—Drift_Tracking TLV . 107
Table 14-3—parentDS table . 116
Table 14-6a—ptpInstanceSyncDS table. 117
Table 14-6b—driftTrackingDS table. 118
Table 14-8—delayMechanism enumeration. 118
Table 14-10—portDS table. 120
Table 14-12—portStatisticsDS table . 121
Table 14-18—cmldsLinkPortDS table . 122
Table 14-15—asymmetryMeasurementModeDS table . 122
Table 14-19—cmldsLinkPortStatisticsDS table.
...