TN-5516/5518 User’s Manual Featured Functions
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Time Server Query Period
Setting Description Factory Default
Query period This parameter determines how frequently the
time is updated from the NTP server.
600 seconds
Enable NTP/SNTP Server
Setting Description Factory Default
Enable/Disable This enables or disables NTP or SNTP server. Disable
Configuring IEEE 1588/PTP
Time may be accomplished using the IEEE Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and Control Systems (IEEE 1588-2008) to synchronize
real-time clocks incorporated within each component of the electrical power system in power
automation applications.
IEEE 1588, published in November 2002, is a new technology that expands the performance
capabilities of Ethernet networks for measurement and control over a communication network. In
recent years, an increasing number of electrical power systems have been utilizing a more
distributed architecture and less stringent timing specifications. IEEE 1588 establishes a
master-slave relationship between the clocks, and enforces the specific timing requirements. All
devices ultimately derive their time from a clock known as the grandmaster clock. In its basic form,
the protocol is intended to be administration free.
How does an Ethernet switch affect 1588 synchronization?
An Ethernet switch potentially introduces multi-microsecond fluctuations in the latency between
the 1588 grandmaster clock and a 1588 slave clock. Uncorrected these fluctuations will cause
synchronization errors. The magnitude of these fluctuations depend on the design of the Ethernet
switch and the details of the communication traffic. Experiments with prototype implementations
of IEEE 1588 indicate that with suitable care the effect of these fluctuations can be successfully
managed. For example, use of appropriate statistics in the 1588 devices to recognize significant
fluctuations and use suitable averaging techniques in the algorithms controlling the correction of
the local 1588 clock will achieve the highest time accuracy.
Can Ethernet switches be designed to avoid the effects of these fluctuations?
A switch may be designed to support IEEE 1588 while avoiding the effects of queuing. In this case
two modifications to the usual design of an Ethernet switch are necessary:
y The Boundary Clock functionality defined by IEEE 1588 must be implemented in the switch,
and
y The switch must be configured such that it does not pass IEEE 1588 message traffic using the
normal communication mechanisms of the switch.
Such an Ethernet switch will synchronize clocks directly connected to one of its ports to the
highest possible accuracy.
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