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01 June 2003

ODVA adopts IEEE 1588

The Open Device Vendors Association (ODVA) announced that it plans to add time synchronization services for real-time control applications to its Common Industrial Protocol (CIP).

With the addition of these services, the organization says that original equipment manufacturers and other manufacturers will benefit from expanded application coverage of DeviceNet and EtherNet/IP systems.

This includes sequence of events recording, distributed motion control, and other highly distributed applications requiring increased control coordination. The organization will base the system—CIPsync—on the recent IEEE-1588 standard.

Kang Lee of the National Institute of Standards and Technology introduced 1588 this way. Measurement and control systems are widely used in traditional test and measurement, industrial automation, communication systems, electrical power systems, and many other areas of modern technology.

The timing requirements placed on these measurement and control systems are becoming increasingly stringent. Traditionally people have implemented these systems in a centralized architecture in which the timing constraints necessitate careful attention to programming, combined with communication technologies with deterministic latency.

In recent years an increasing number of such systems utilize a more distributed architecture, and increasingly networking technologies have less stringent timing specifications than the older more specialized technologies. In particular Ethernet communications are becoming more common in measurement and control applications.

This has led to alternate means for enforcing the timing requirements in such systems. One such technique is using system components that contain real-time clocks, all of which synchronize with each other within the system. This is very common in the general computing industry.

For example, essentially all general-purpose computers contain a clock. These clocks are used to manage distributed file systems, backup and recovery systems, and many other similar activities.

These computers typically interact via local area networks and the Internet. In this environment the most widely used technique for synchronizing the clocks is the Network Time Protocol or the related Simple Network Time Protocol.

Measurement and control systems have a number of requirements that a clock synchronization technology must meet. In particular:

• Timing accuracy must be in the submicrosecond range.
• The technologies must be available on a range of networking technologies, including Ethernet, but also on other technologies found in industrial automation and similar industries.
• Administration should be minimal.
• The technology must be capable of implementation on low cost and low-end devices.
• The required network and computing resources should be minimal.

In contrast to the general computing environment of intranets or the Internet, measurement and control systems typically are more spatially localized.

IEEE 1588 addresses the clock synchronization requirements of measurement and control systems.

It defines a protocol that enables precise synchronization of clocks in measurement and control systems with technologies such as network communication, local computing, and distributed objects.

The protocol will be applicable to systems communicating by local area networks supporting multicast messaging including, but not limited to, Ethernet. The protocol will enable heterogeneous systems that include clocks of various inherent precisions, resolutions, and stabilities to synchronize. The default behavior of the protocol will allow simple systems to install and operate without requiring the administrative attention of users.

"ODVA's adoption of the IEEE-1588 standard validates its significance as a key enabling technology for next-generation industrial networks," said John C. Eidson, chairperson of the IEEE-1588 working group.

"CIPsync will simplify installations using industrial Ethernet for real-time control," said Katherine Voss, ODVA executive director. IT

Nicholas Sheble writes and edits the Fieldbus News department. Write him at nsheble@isa.org.