Moxa EDS-G516E-4GSFP — преимущества управляемых Ethernet-коммутаторов для синхронизации IEEE 1588 [25/116]

Managed Ethernet Switch (UI_2.0_FW_5.x) Featured Functions

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IEEE 1588 PTP

The following information is taken from the NIST website at http://ieee1588.nist.gov/intro.htm:

“Time measurement can 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 for power automation applications.

IEEE 1588, which was published in November 2002, expands the performance capabilities of Ethernet networks

to control systems that operate over a communication network. In recent years an increasing number of

electrical power systems have been using a more distributed architecture with network technologies that have

less stringent timing specifications. IEEE 1588 generates a master-slave relationship between the clocks, and

enforces the specific timing requirements in such power systems. All devices ultimately get 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?

The following content is taken from the NIST website at http://ieee1588.nist.gov/switch.htm:

“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 depends 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 be good design means to achieve the highest time

accuracy.”

Can Ethernet switches be designed to avoid the effects of these

fluctuations?

A switch can 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:

1. The Boundary Clock and Transparent Clock functionalities defined by IEEE 1588 must be implemented

in the switch.

2. The switch must be configured so 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.