User`s manual

PT-G7509 User’s Manual Featured Functions
3-11
Time Server IP/Name
Setting Description Factory Default
IP address or name of time
server
This is the IP or domain address (e.g.,
192.168.1.1, time.stdtime.gov.tw, or
time.nist.gov).
IP address or name of
secondary time server
The PT-G7509 will try to locate the secondary
NTP server if the first NTP server fails to
connect.
None
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 synchronization 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:
• The Boundary /Transparent Clock functionality defined by IEEE 1588 must be
implemented in the switch, and
• The switch must be configured such that it does not pass IEEE 1588 message traffic using the
normal communication mechanisms of the switch.