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Watch Your Ethernet Definitions

If I mention the word “Ethernet,” what’s the first thing that comes to mind?

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Well, you’re probably wrong. Ethernet technically describes only the physical layer of the network. It encompasses the cable, connector and the lowest layer firmware needed to effect an electrical connection. When I took my first networking classes around 1987, Ethernet was barely discussed, even though it did exist at the time. It was almost a surprise when, as it seemed, Ethernet suddenly became the personal computing and client/server network almost everywhere.

We use the term in this magazine in a way reflecting general usage. We not only refer to the physical layer, but also to the whole host of transmission, addressing and application layer protocols that have grown up over the years. Many grew because the early Web browsers supported the application protocols. The hypertext transfer protocol (http) that enables Web page loading and the file transfer protocol (ftp) that enables transmitting large files are a couple of examples.

The beauty of Ethernet and the standards and practices that have grown up around it lies in the network’s openness and flexibility. The way it is designed, it can carry all of the protocols at the same time on the same wire—and the messages don’t become garbled.

Terry Costlow does an admirable job describing a variety of these protocols and explaining their use. This is the foundation article of our new year of bringing you the Industrial Ethernet Review. Enjoy.

To take a deeper dive into the topic; check out the on-demand Webcast, “Ethernet-based Industrial Communication Protocols” at

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