14 GEN series Synchronization Methods
14.1
PTP
14.1.1
PTP technology background
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Source: Wikipedia
®
the free encyclopedia
The
Precision Time Protocol (PTP)
is a protocol used to synchronize clocks
throughout a computer network. On a local area network, it achieves clock
accuracy in the sub
-
microsecond range, making it suitable for measurement
and control systems.
PTP was originally defined in the
IEEE 1588
-
2002
standard, officially entitled
"Standard for a Precision Clock Synchronization Protocol for Networked
Measurement and Control Systems"
and published in 2002. In 2008, a revised
standard,
IEEE 1588
-
2008
was released. This new version, also known as PTP
Version 2, improves accuracy, precision and robustness but is not backwards
compatible with the original 2002 version.
Architecture
The IEEE 1588 standards describe a hierarchical master
-
slave architecture for
clock distribution. Under this architecture, a time distribution system consists of
one or more types of communication media (network segments) and one or
more clocks. An ordinary clock is a device with a single network connection and
is either the source (master) of or destination (slave) for a synchronization
reference. A boundary clock has multiple network connections and can
accurately bridge synchronization from one network segment to another. A
synchronization master is selected for each of the network segments in the
system. The root timing reference is called the grandmaster. The grandmaster
transmits synchronization information to the clocks residing on its network
segment.
The boundary clocks with a presence on that segment then relay accurate time
to the other segments to which they are also connected.
A simplified PTP system frequently consists of ordinary clocks connected to a
single network. No boundary clocks are used. A grandmaster is elected and all
other clocks synchronize directly to it. IEEE 1588
-
2008 introduces a clock
associated with network equipment used to convey PTP messages. The
transparent clock modifies PTP messages as they pass through the device.
Timestamps in the messages are corrected for time spent traversing the
network equipment. This scheme improves distribution accuracy by
compensating for delivery variability across the network.
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