IEEE 1588-2019：精密时钟同步协议详解

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"IEEE 1588协议是网络化测量和控制系统中精确时钟同步协议的标准，由IEEE仪表与测量学会的传感器技术技术委员会（TC-9）开发。该标准于2019年进行了修订，即IEEE Std 1588-2019，是对2008版的更新，旨在为基于包的网络系统中的时钟提供精确的同步能力。" 在现代网络通信中，特别是在自动化、电力系统、电信和数据网络等领域，精确的时间同步至关重要。IEEE 1588协议，也称为精确时间协议（PTP），是一种用于实现这种同步的方法。该协议允许网络中的设备共享一个准确的时间参考，确保所有操作都能够在同一时间点进行，从而提高系统的效率和准确性。 IEEE Std 1588-2019的核心目标是在异构系统中实现时钟同步，这意味着不同类型的设备，包括具有不同硬件和软件平台的设备，都能够协调它们的时钟，达到微秒甚至纳秒级的精度。这在需要精确时间戳的多种应用中极其重要，例如分布式系统、实时数据采集、金融交易记录和电力系统频率控制。协议的主要组成部分包括： 1. 主时钟（Grandmaster）：网络中提供准确时间参考的设备。 2. 从时钟（Slave）：从主时钟接收时间信息并调整其内部时钟的设备。 3. 时间戳：在数据包中附加的时间信息，用于计算和校正传输延迟。 4. 报文交换：主时钟和从时钟之间通过特定的消息（如Sync、Follow-Up和Delay_Req/Resp）进行通信，以确定时间差并进行调整。 5. 精度和适应性：协议设计考虑到网络条件的变化，能够动态调整以适应各种网络延迟和抖动。该协议的2019修订版可能包含对旧版的改进，如增强的性能、更高的精度、更佳的网络适应性和兼容性，以及可能的新功能，以应对不断发展的技术需求和挑战。例如，可能增加了对IPv6的支持，提高了在复杂网络环境下的同步效率，或者优化了时钟同步算法以减少错误和漂移。 IEEE 1588-2019是网络时钟同步的基石，它允许设备在分布式系统中协同工作，确保了数据的准确性和一致性，对于依赖时间敏感操作的现代技术是不可或缺的。

IEEE Std 1588-2019

IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems

2. Normative references

The following referenced documents are indispensable for the application of this document (i.e., they must

be understood and used, so each referenced document is cited in text and its relationship to this document is

explained). For dated references, only the edition cited applies. For undated references, the latest edition of

the referenced document (including any amendments or corrigenda) applies.

FIPS PUB 180-4:2015, Secure Hash Standard.

FIPS PUB 198-1:2008, The Keyed-Hash Message Authentication Code (HMAC).

IEC 61158-5-10:2007, Industrial communication networks

—Fieldbus specifications—Part 5-10:

Application layer service definition

—Type 10 elements.

IEC 61158-6-10:2007, Industrial communication networks

—Fieldbus specifications—Part 6-10:

Application layer protocol specification

—Type 10 elements.

IEC 61784-1:2007, Industrial communication networks

—Profiles—Part 1: Fieldbus profiles.

IEC 61784-2:2007, Industrial communications networks

—Profiles—Part 2: Additional fieldbus profiles for

real-time networks based on ISO/IEC 8802-3.

IEC 62026-3:2008, Low-voltage switchgear and controlgear

—Controller-device interfaces (CDIs)—Part 3:

DeviceNet.

IEEE Std 754™, IEEE Standard for Binary Floating-Point Arithmetic.

IEEE Std 802

, IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture.

IEEE Std 802.1AS™-2011, IEEE Standard for Local and Metropolitan Area Networks—Timing and

Synchronization for Time-Sensitive Applications in Bridged Local Area Networks.

IEEE Std. 802c™, Standard for Local and Metropolitan Area Networks—Overview and Architecture

Amendment: Local Medium Access Control (MAC) Address Usage.

IEEE Std 802.1Q™

-2014, IEEE Standard for Local and Metropolitan Area Networks—Bridges and

Bridged Networks.

IEEE Std 802.3™, IEEE Standard for Ethernet.

IEEE Std. 802.11™, IEEE Standard for Information technology—Telecommunications and information

exchange between systems—Local and metropolitan area networks—Specific requirements—

Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.

IERS Bulletin C.

IETF RFC 768 (1980), User Datagram Protocol, Postel, J., ed.

IETF RFC 791 (1981), Internet Protocol, Postel, J., ed.

FIPS publications are available from the National Technical Information Service, U. S. Department of Commerce

(http://www.ntis.org/).

IEC publications are available from the International Electrotechnical Commission (http://www.iec.ch) and the American National

Standards Institute (http://www.ansi.org/).

IEEE publications are available from The Institute of Electrical and Electronics Engineers (http://standards.ieee.org/).

The IEEE standards or products referred to in Clause 2 are trademarks owned by The Institute of Electrical and Electronics

Engineers, Incorporated.

IERS publications are available from the International Earth Rotation and Reference Systems Services (https://www.iers.org/).

IETF publications are available from the Internet Engineering Task Force (https://www.ietf.org/).

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IEEE Std 1588-2019

IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems

IETF RFC 1624 (1994), Computation of the Internet Checksum via Incremental Update,

Rijsinghani, A., ed.

IETF RFC 4868 (2007), Using HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512 with IPsec,

Kelly, S., and Frankel, S., eds.

IETF RFC 8200 (2017), Internet Protocol, Version 6 (IPv6) Specification, Deering, S., and Hinden, R., eds.

ISO/IEC 10646:2003, Information technology

—Universal Multiple-Octet Coded Character Set (UCS)—

Part 1: Architecture and Basic Multilingual Plane.

3. Definitions, acronyms, and abbreviations

3.1 Definitions

For the purposes of this document, the following terms and definitions apply.

3.1.1 accuracy: The mean over an ensemble of measurements of the time or frequency error between the

clock under test and a reference clock.

NOTE 1— Line “B” in Figure 1 represents the error in the measured mean value with respect to the reference, that is,

the accuracy. The width of the curve of ensemble measurements, “C” in Figure 1, represents the measurement

precision.

Reference

clock value

Measured

mean value

Figure 1Histogram of an ensemble of measurements

NOTE 2— Different industries define "accuracy" in differing ways; however, for the discussion of an IEEE 1588

Grandmaster Clock, a smaller mean or maximum error from the reference time scale will be considered more accurate

(whether the mean error or the maximum error is more relevant depends on the application).

3.1.2 atomic process: A process in which all the values of all inputs to the process are not permitted to

change until all the results of the process are instantiated, and the outputs of the process are not visible to

other processes until the processing of each output is complete.

ISO publications are available from the International Organization for Standardization (http://www.iso.org/) and the American

National Standards Institute (http://www.ansi.org/).

Notes in text, tables, and figures of a standard are given for information only and do not contain requirements needed to implement

this standard.

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IEEE Std 1588-2019

IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems

3.1.3 Boundary Clock: A PTP Instance that has multiple PTP Ports in a domain and maintains the

timescale used in the domain. Within a domain, it may serve as the source of time to other PTP Instances,

that is, be a Master Clock, and it can in addition synchronize to another Boundary Clock or Ordinary Clock,

that is, be a Slave Clock.

3.1.4 clock: A device that can provide a measurement of the passage of time since a defined epoch.

NOTE 1— There are only two types of clocks specified in this standard: the Local PTP Clock and the Local Clock.

NOTE 2—

For Local PTP Clocks associated with Ordinary Clocks and Boundary Clocks that are properly

synchronized, the epoch is the epoch of the timescale in use. In the case of a Local Clock associated with a

Transparent Clock, the epoch is locally defined and not necessarily aligned with the timescale in use.

NOTE 3— A clock provides time at desired moments of the timescale it maintains. Time is obtained either:

 Physically: in this type of clock, the time is modeled using a clock signal and a time counter that is

driven by the clock signal;

 Mathematically: in this type of clock, the time is generated by a model that describes the relation of

this clock to another clock (e.g., to a physical clock in a different timescale). The model enables the

calculation of the time of the clock from the time of the other clock.

NOTE 4— The word “clock” appears many times in this standard modified as Boundary Clock, Ordinary

Clock, Transparent Clock, or Grandmaster Clock. When used this way the combination, e.g. Boundary

Clock, is not a clock as defined here but rather contains a clock. For historical reasons, these terms have

been retained.

3.1.5 clock signal: A physical signal that has periodic events. The periodic events mark the significant

instants at which a time counter is incremented. The clock signal is characterized by its frequency and

phase.

3.1.6 default: When applied to attribute values and options of a PTP Instance, “default” means the

configuration of a PTP Instance as it is delivered from the manufacturer.

3.1.7 device: An entity implementing some functionality, for example, a clock, a Boundary Clock, an

encoder, and a port. See also: PTP Instance.

3.1.8 Direct PTP Link: A direct physical link with no intervening network elements between two PTP

Ports of Boundary Clocks, Ordinary Clocks, and/or peer-to-peer Transparent Clocks.

NOTE 1— A direct physical link, where at least one end point is a PTP Port of an end-to-end Transparent Clock, is not

a Direct PTP Link.

NOTE 2— A Direct PTP Link is a PTP Communication Path if the delay request-response mechanism is used. It is a

PTP Link if the peer-to-peer delay mechanism is used, and is at the same time a PTP Communication Path if it is

between two Boundary Clocks, two Ordinary Clocks, or a Boundary Clock and an Ordinary Clock.

3.1.9 domain (or PTP Domain): A logical grouping of PTP Instances using PTP to ensure that all Local

PTP Clocks in the grouping are synchronized to the Grandmaster Clock of the domain, but are not

necessarily synchronized to the Local PTP Clocks in another domain.

3.1.10 end-to-end port: A PTP Port that is configured to use the delay request-response mechanism.

3.1.11 end-to-end Transparent Clock: A Transparent Clock that supports the use of the delay request-

response mechanism between a PTP Port in the MASTER state and a PTP Port in the SLAVE state in the

same domain.

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IEEE Std 1588-2019

IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems

3.1.12 epoch: The origin of a timescale.

3.1.13 event: An abstraction of the mechanism by which signals or conditions are generated and

represented. In this abstraction, the aspects of interest of the signals are conditions that occur at discrete

instants of time.

3.1.14 foreign master: If an Announce message is received on PTP Port a of PTP Instance A from PTP

Port b of PTP Instance B in the same PTP Network, and PTP Port b is not the current Master of PTP Port a,

then PTP Port b is considered a foreign master by PTP Port a.

3.1.15 fractional frequency offset: The fractional frequency offset (FFO) between a measured frequency

and a reference frequency is defined as follows:

(FO FR)

FFO

−

(1)

where

FO is the measured frequency

FR is the reference frequency

3.1.16 frequency offset: The frequency offset between a measured frequency and a reference frequency is

defined as follows:

Frequency Offset FO FR = −

(2)

where

FO is the measured frequency,

FR is the reference frequency.

3.1.17 Grandmaster Clock: In the context of a single PTP domain, the Local PTP Clock of an Ordinary

Clock or a Boundary Clock that is the source of time to which all other Local PTP Clocks in the domain are

synchronized.

3.1.18 Grandmaster PTP Instance: A PTP Instance containing the Grandmaster Clock.

3.1.19 holdover or holdover mode: A clock A, previously synchronized/syntonized to another clock B

(normally a primary reference or a Master Clock) but whose frequency is determined in part using data

acquired while it was synchronized/syntonized to B, is said to be in holdover or in the holdover mode as

long as it is within its accuracy requirements.

3.1.20 implemented message timestamp point: A point within a Precision Time Protocol event message

serving as a timestamp-capture point in the message. A timestamp is captured at the instant an implemented

message timestamp point passes a point possibly removed from the reference plane. Depending on the

implementation, the implemented message timestamp point is or is not equivalent to the message

timestamp point. See: message timestamp point.

NOTE—The relationship between the two is specified in 7.3.4.2.

3.1.21 integrity check value (ICV): The result of a cryptographic function used to ensure that

unauthorized modifications of a message are detected (e.g., the value might be the result of the keyed hash

function HMAC-SHA256.

NOTE—See FIPS PUB 180-4:2015.

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IEEE Std 1588-2019

IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems

3.1.22 key: In the context of a security association, refers to the secret used in the cryptographic calculation

of the integrity check value (ICV).

3.1.23 key distribution center (KDC): The functionality of a (typically) centralized authority to which

peers authenticate before distribution of security parameters. For instance, KDCs are used to distribute

security parameters for group-based communication.

3.1.24 L1 rx clock signal: A clock signal that is recovered from the reception of data from the medium.

3.1.25 L1 tx clock signal: A clock signal that is used in the transmission of data over the medium.

3.1.26 Local Clock: A physical clock that is used in the operation of the PTP Protocol.

 The Local PTP Clock may be derived from or identical to the Local Clock;

 The Local Clock may be syntonized to a reference clock signal.

NOTE—See 12.2.

3.1.27 Local Clock signal: The clock signal of a Local Clock.

3.1.28 Local PTP Clock: The clock of a PTP Instance that provides the local estimate of the time of its

Grandmaster Clock, that is it is synchronized to the time of the Grandmaster Clock. It is either a physical or

a mathematical clock, and it provides PTP or ARB (arbitrary) time.

NOTE—See 7.2.1.

3.1.29 Local PTP Clock signal: The clock signal of a Local PTP Clock.

3.1.30 management mechanism: A management protocol used for configuring and/or monitoring PTP

Nodes and PTP Instances.

NOTE—This term refers to the PTP management messages of this standard, as well as to the management protocols

defined in other standards (e.g., SNMP [B27]

and NETCONF [B20]).

3.1.31 Master Clock: In the context of a single PTP Communication Path, the Local PTP Clock of an

Ordinary Clock or Boundary Clock that is the source of time to which all other Local PTP Clocks on that

PTP Communication Path synchronize.

3.1.32 Master PTP Instance: A PTP Instance containing a Master Clock.

NOTE—A Master PTP Instance propagates the traceability information from the Grandmaster PTP Instance

throughout the associated PTP Communication Path.

3.1.33 message timestamp point: A point within a PTP event message serving as a reference point in the

message. A timestamp is defined by the instant a message timestamp point passes the reference plane of a

PTP Instance.

3.1.34 mixed-step PTP Instance: A PTP Instance where some PTP Ports can be one-step PTP Ports and

one or more PTP Ports can be two-step PTP Ports, see one-step PTP Port and two-step PTP Port.

3.1.35 multicast communication: A communication model in which each PTP message sent from any

PTP Port is received and processed by all PTP Ports on the same PTP Communication Path.

The numbers in brackets correspond to those of the bibliography in Annex Q.

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