ISO/IEC/IEEE 8802-1AS:2021

INTERNATIONAL IS O/IEC/
STANDARD IEEE
8802-1AS
Second edition
2021-11
Information technology —
Telecommunications and information
exchange between systems — Local
and metropolitan area networks —
Part 1AS:
Timing and synchronization for time-
sensitive applications in bridged local
area networks
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
Reference number
© IEEE 2020
© IEEE 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from IEEE at the address below.
Institute of Electrical and Electronics Engineers, Inc
3 Park Avenue, New York
NY 10016-5997, USA
Email: stds.ipr@ieee.org
Website: www.ieee.org
Published in Switzerland
ii
© IEEE 2020 – All rights reserved

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical activity.
ISO and IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the
work.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO/IEC documents should be noted (see www.iso.org/directives or
www.iec.ch/members_experts/refdocs).
IEEE Standards documents are developed within the IEEE Societies and the Standards Coordinating
Committees of the IEEE Standards Association (IEEE-SA) Standards Board. The IEEE develops its
standards through a consensus development process, approved by the American National Standards
Institute, which brings together volunteers representing varied viewpoints and interests to achieve the
final product. Volunteers are not necessarily members of the Institute and serve without compensation.
While the IEEE administers the process and establishes rules to promote fairness in the consensus
development process, the IEEE does not independently evaluate, test, or verify the accuracy of any of the
information contained in its standards.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights. Details
of any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents) or the IEC list of patent
declarations received (see patents.iec.ch).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the World
Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT),
see www.iso.org/iso/foreword.html. In the IEC, see www.iec.ch/understanding-standards.
ISO/IEC/IEEE 8802-1AS was prepared by the LAN/MAN of the IEEE Computer Society (as IEEE Std
802.1AS-2020) and drafted in accordance with its editorial rules. It was adopted, under the “fast-track
procedure” defined in the Partner Standards Development Organization cooperation agreement between
ISO and IEEE, by Joint Technical Committee ISO/IEC JTC 1, Information technology, Subcommittee SC 6,
Telecommunications and information exchange between systems.
A list of all parts in the ISO/IEC/IEEE 8802 series can be found on the ISO and IEC websites.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html and www.iec.ch/national-
committees.
© IEEE 2020 – All rights reserved iii

Abstract: Protocols, procedures, and managed objects for the transport of timing over local are a
networks are defined in this standard. It includes the transport of synchronized time, the selection
of the timing source (i.e., best master), and the indication of the occurrence and magnitude of
timing impairments (i.e., phase and frequency discontinuities).
Keywords: best master, frequency offset, Grandmaster Clock, Grandmaster PTP Instance,
PTP End Instance, PTP Relay Instance, IEEE 802.1AS™, phase offset, synchronization,
syntonization, time-aware system
The Institute of Electrical and Electronics Engineers, Inc.
3 Park Avenue, New York, NY 10016-5997, USA
All rights reserved. Published 19 June 2020. Printed in the United States of America.
MoCA is a registered trademark of the Multimedia over Coax Alliance.
POSIX is a registered trademark of The Institute of Electrical and Electronics Engineers, Incorporated.
IEEE and IEEE 802 are registered trademarks in the U.S. Patent & Trademark Office, owned by The Institute of Electrical and Electronics
Engineers, Incorporated.
PDF: ISBN 978-1-5044-6430-7 STD24046
Print: ISBN 978-1-5044-6431-4 STDPD24046
IEEE prohibits discrimination, harassment and bullying.
For more information, visit https://www.ieee.org/about/corporate/governance/p9-26.html.
No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission
of the publisher.
Important Notices and Disclaimers Concerning IEEE Standards
Documents
IEEE documents are made available for use subject to important notices and legal disclaimers. These notices and
disclaimers, or a reference to this page, appear in all standards and may be found under the heading “Important Notice s
and Disclaimers Concerning IEEE Standards Documents.” They can also be obtained on request from IEEE or viewed at
https://standards.ieee.org/ipr/disclaimers.html.
Notice and Disclaimer of Liability Concerning the Use of IEEE Standards
Documents
IEEE Standards documents (standards, recommended practices, and guides), both full-use and trial-use, are develope d
within IEEE Societies and the Standards Coordinating Committees of the IEEE Standards Association (“IEEE SA”)
Standards Board. IEEE (“the Institute”) develops its standards through a consensus development process, approved by the
American National Standards Institute (“ANSI”), which brings together volunteers representing varied viewpoints an d
interests to achieve the final product. IEEE Standards are documents developed through scientific, academic, and industry-
based technical working groups. Volunteers in IEEE working groups are not necessarily members of the Institute and
participate without compensation from IEEE. While IEEE administers the process and establishes rules to promote fairnes s
in the consensus development process, IEEE does not independently evaluate, test, or verify the accuracy of any of th e
information or the soundness of any judgments contained in its standards.
IEEE Standards do not guarantee or ensure safety, security, health, or environmental protection, or ensure against
interference with or from other devices or networks. Implementers and users of IEEE Standards documents are responsibl e
for determining and complying with all appropriate safety, security, environmental, health, and interference protection
practices and all applicable laws and regulations.
IEEE does not warrant or represent the accuracy or content of the material contained in its standards, and expressly
disclaims all warranties (express, implied and statutory) not included in this or any other document relating to the standard,
including, but not limited to, the warranties of: merchantability; fitness for a particular purpose; non-infringement; an d
quality, accuracy, effectiveness, currency, or completeness of material. In addition, IEEE disclaims any and all condition s
relating to: results; and workmanlike effort. IEEE standards documents are supplied “AS IS” and “WITH ALL FAULTS.”
Use of an IEEE standard is wholly voluntary. The existence of an IEEE standard does not imply that there are no other way s
to produce, test, measure, purchase, market, or provide other goods and services related to the scope of the IEEE standard.
Furthermore, the viewpoint expressed at the time a standard is approved and issued is subject to change brought about
through developments in the state of the art and comments received from users of the standard.
In publishing and making its standards available, IEEE is not suggesting or rendering professional or other services for, or
on behalf of, any person or entity nor is IEEE undertaking to perform any duty owed by any other person or entity to
another. Any person utilizing any IEEE Standards document, should rely upon his or her own independent judgment in th e
exercise of reasonable care in any given circumstances or, as appropriate, seek the advice of a competent professional i n
determining the appropriateness of a given IEEE standard.
IN NO EVENT SHALL IEEE BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO: PROCUREMENT OF SUBSTITUTE
GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TOR T
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE PUBLICATION, USE OF, OR
RELIANCE UPON ANY STANDARD, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE AND
REGARDLESS OF WHETHER SUCH DAMAGE WAS FORESEEABLE.
Translations
The IEEE consensus development process involves the review of documents in English only. In the event that an IEEE
standard is translated, only the English version published by IEEE should be considered the approved IEEE standard.
Official statements
A statement, written or oral, that is not processed in accordance with the IEEE SA Standards Board Operations Manual shall
not be considered or inferred to be the official position of IEEE or any of its committees and shall not be considered to be, or
be relied upon as, a formal position of IEEE. At lectures, symposia, seminars, or educational courses, an individual
presenting information on IEEE standards shall make it clear that his or her views should be considered the personal views
of that individual rather than the formal position of IEEE.
Comments on standards
Comments for revision of IEEE Standards documents are welcome from any interested party, regardless of membership
affiliation with IEEE. However, IEEE does not provide consulting information or advice pertaining to IEEE Standard s
documents. Suggestions for changes in documents should be in the form of a proposed change of text, together wit h
appropriate supporting comments. Since IEEE standards represent a consensus of concerned interests, it is important that
any responses to comments and questions also receive the concurrence of a balance of interests. For this reason, IEEE and
the members of its societies and Standards Coordinating Committees are not able to provide an instant response t o
comments or questions except in those cases where the matter has previously been addressed. For the same reason, IEEE
does not respond to interpretation requests. Any person who would like to participate in revisions to an IEEE standard i s
welcome to join the relevant IEEE working group.
Comments on standards should be submitted to the following address:
Secretary, IEEE SA Standards Board
445 Hoes Lane
Piscataway, NJ 08854 USA
Laws and regulations
Users of IEEE Standards documents should consult all applicable laws and regulations. Compliance with the provisions of
any IEEE Standards document does not imply compliance to any applicable regulatory requirements. Implementers of th e
standard are responsible for observing or referring to the applicable regulatory requirements. IEEE does not, by th e
publication of its standards, intend to urge action that is not in compliance with applicable laws, and these documents ma y
not be construed as doing so.
Copyrights
IEEE draft and approved standards are copyrighted by IEEE under US and international copyright laws. They are mad e
available by IEEE and are adopted for a wide variety of both public and private uses. These include both use, by reference,
in laws and regulations, and use in private self-regulation, standardization, and the promotion of engineering practices an d
methods. By making these documents available for use and adoption by public authorities and private users, IEEE does not
waive any rights in copyright to the documents.
Photocopies
Subject to payment of the appropriate fee, IEEE will grant users a limited, non-exclusive license to photocopy portions of
any individual standard for company or organizational internal use or individual, non-commercial use only. To arrange for
payment of licensing fees, please contact Copyright Clearance Center, Customer Service, 222 Rosewood Drive, Danvers,
MA 01923 USA; +1 978 750 8400. Permission to photocopy portions of any individual standard for educational classroom
use can also be obtained through the Copyright Clearance Center.
Updating of IEEE Standards documents
Users of IEEE Standards documents should be aware that these documents may be superseded at any time by the issuanc e
of new editions or may be amended from time to time through the issuance of amendments, corrigenda, or errata. An official
IEEE document at any poi
...