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Appendix B – PTP Standard Concepts (IEEE1588)
Description
Definitions according to IEEE 1588 Standard
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The Precision Time Protocol (PTP) is an ultimate time synchronization accuracy
protocol for Ethernet networks. On a local area network, it achieves clock accuracy in
the sub-micro second range, making it suitable for applications where
synchronization is essential to the measurement system. The ultimate time accuracy
of the protocol is obtained from the compensation of propagation delay information
between the source and destination.
IEEE 1588 - 2002 standard, officially entitled "Standard for a Precision Clock
Synchronization Protocol for Networked and Control Systems", originally defined PTP
protocol. In 2008, the standard was revised and had its protocol accuracy and
robustness improved.
The protocol describes a hierarchical master-slave architecture designed for clock
distribution, where the root timing reference is called Grandmaster clock, which
transmits synchronization information to the clocks residing on its network segment.
Clock: IEEE1588 standard defines a clock as a network device capable of using
PTP protocol and providing a measurement of the passage of time since a
defined epoch.
Synchronized Clocks: According to IEEE1588 standard, two clocks are
synchronized to a specified uncertainty if they have the same epoch and their
measurements of time of a single event at an arbitrary time differ by no more
than that uncertainty.
Master Clock: According to IEEE1588, it is a clock that is the source of time to
which all other clocks on that path synchronize.
Grandmaster Clock: IEEE1588 defines a grandmaster clock, within a domain, as
a clock that is the ultimate source of time for clock synchronization using the
protocol.
Slave Clock: IEEE1588 defines a slave clock as a clock that is coordinated with a
master clock, i.e., it is capable of recognizing time Sync messages from a master
clock.
Best Master Clock Algorithm: According to IEEE1588, The Best Master Clock
algorithm (BMC) performs a distributed selection of the best candidate clock to
be used as clock source based on the following clock properties:
A universally unique numeric identifier for the clock. This is typically
o
constructed based on a device's MAC address.
Time information quality is based on the time system adopted as reference.
o
Priority assigned to a clock in its configuration.
o
Clock variance, which represents its stability based on observation of its
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performance over time.
The algorithm establishes an order of searching for the attributes and from the
results, determines which will be used as time source.
Boundary Clock: According to IEEE1588 standard, a boundary clock has multiple
PTP ports in a domain and maintains the timescale used in the domain. It may
Chapter 10 - Appendixes
RT430/434
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