Interoperability 101: The Basics of an Interoperable Grid

 In my first column, Smart Grid Standards Done Right, I laid out the benefits of standards and the hurdles along the way. In particular, I stressed the need for “industrial-scale” integration across multiple communities. I proposed an open discussion of the key elements and promised to begin with the basics of interoperability.  In this second article, I will lay out “Interoperability 101” with emphasis on the multiple layers of interoperability. With these basics out of the way, we’ll be ready to move to a discussion of interoperability architectures.

Interoperability is the ability of two devices to exchange information and do useful work.  But what does it take for two devices from different vendors to work together? And to do so over a network?  Interoperable equipment has many elements, and they all need to line up technically or nothing happens. 

To understand the challenges, let’s start by looking at interoperability at the device level and then “zoom out” to the industry level to explain the roles of formal industry standards, user interoperability agreements, technology transfer, and industry architecture development.

The Complexity of a Simple Standard

The phrase “distributed computing” is essential to understanding interoperable systems. Distributed computing includes both communications processes (the exchange of well-understood data and information) and computer applications (the performance of a useful function).

USB thumb drives (also known as flash drives or memory sticks) are the most widely known “simple” example of distributed computing.  Once plugged in, a thumb drive initiates process-level communications with the other device (the computer, typically).  These communications provide the physical media through the physical plug and internal wiring. They also exchange “well-understood” messages. The first “words” exchanged are typically housekeeping issues such as the type of device, the rate of info exchange, and other information to set up the relationship. The USB standard then supports the data exchange as, for example, files are dragged and dropped from one device to another.

The USB standard provides the common ground so multiple vendors can build equipment that will work together. As it turns out, this interoperability example appears simple but is complex under the covers.  The USB standard is a substantial, detailed document.

The Challenges of Network Interoperability

Interoperable systems require exquisite attention to detail. Unlike human communications where there is room to interpret, machines only respond to exact meanings. Communications, management, security, and application execution messages must all be well understood by the interoperating equipment. Interoperability over a network only compounds the amount of detail required.

Connecting two devices physically is only one dimension of interoperability and is often the easiest step. Connecting them through a network adds another level of complexity that must be agreed upon by all the networking elements. As the two devices attempt to exchange data, the messages must now speak the language of network navigation and be properly “addressed” to reach the destination device.  This sounds simple, but to machines these are complex processes. Those complexities must be spelled out in standards.  The field of networking standards is not trivial since it encompasses the management of all network resources as well as the messaging. The science of large-scale network operations is still maturing as are network architectures.

Adding Application Interoperability

Getting a message from one device and through the network to arrive at the destination only achieves an initial level of “network communications interoperability.”  The interoperability challenge now continues in the destination device, which must be able to read the message and take action on it.  This requires a different set of standards for message semantics and syntax.  Application interoperability is achieved if the correct action takes place in the destination device.  That requires common language semantics and syntax that applications understand.

Even deeper levels of interoperability will be necessary for energy system equipment to act like USB thumb drives and achieve “plug-and-work” interoperability.  This level is necessary for carrying out a variety of functions behind the scenes. The exchange of data behind the scenes is called metadata and is the key to making the USB drives easy for the end users.  Metadata is information that describes data.  I know it sounds like double talk, but metadata is necessary for devices to “introduce” and configure themselves without direct human involvement.

These deeper levels of interoperability include a lot of details and are necessary to many systems administration processes.  All this takes agreement among the vendors building products.

Why Standards Need User Groups

Standards are necessary ingredients but are insufficient by themselves to achieve interoperable equipment.  The formal standards process arrives at a consensus through contributed documents, discussions, and formal voting. The resulting standard generally includes compromises, multiple options, and may even leave a few items undefined.  This is not an indictment of the standards process but a recognition of the reality of building a consensus.  Formal standards are good for providing a measure of stability for vendors, but they often need to be augmented. That’s where user groups come in.

User implementation agreements reduce the number of options.  User groups often take on this role and develop a synergy with the formal standard.  User groups are also involved in resolving details and often get involved with conformance testing.  In the power industry, user groups such as the UCA International Users Group and the Association of Edison Illuminating Companies Metering Working Group have taken on some of these roles. 

We are still not done with the interoperability discussion. The big challenge is getting not one but multiple industries to agree on the details for equipment that can be sold worldwide.  These concepts relate to both enterprise and industry architectures that provide the framework or “architecture” of an overall interoperability plan.

In my next article, I’ll talk about how to define and document an architecture for interoperability.

Joe Hughes is Senior Technical Manager of EPRI Power Delivery. His background includes 25 years in energy industry research and standards development. He will be presenting at the Grid-Interop Conference Nov. 11-13, 2008, in Atlanta, GA.

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   Joe Hughes’ first SGN article “Smart Grid Standards Done Right”

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