Cat-Scratch Fever

Last month, I discussed the evolution of PC networks to Ethernet over twisted-pair cables. Toward the end of the 1980s, the IEEE created a new standard for Ethernet called 10Base-T, which means 10 megabits per second (Mbps), baseband (AM, not FM) over unshielded twisted-pair (UTP) copper cable. Then the fun began.

The IEEE Ethernet specification defined the electrical specifications of the transmitters and receivers but was not that specific on the cable. Dozens of manufacturers made the cable, but nobody knew which twisted-pair wire would work with 10Base-T. What performance specifications were important in determining how well it would work? How critical were the installation processes?

It quickly became apparent that the performance of the wire was critical to this version of Ethernet meeting its 100-meter length specification. Wire made for plain old telephone service (POTS) was found to be inadequate.

As it became more frustrating for everyone involved, one big cabling distributor, Anixter, came to the rescue. The company equipped a comprehensive cabling lab and hired cable engineer Pete Lockhart to run it. The lab tested and graded UTP cables and set its own specifications for several grades of cable, which it called “Levels.” Level 1 was POTS cable, Level 2 was for slower IBM systems and Level 3 was the cable for 10Base-T.

Anixter’s rationale is best expressed in its own words from an old Levels brochure: “The goal in creating Levels was simple: to help customers easily select and design a reliable data cabling infrastructure that allows them to run their current and future applications.”

Soon after Levels was introduced, the Electronics Industry Association (EIA) assembled the TR42 committee to create an industry-wide standard for cabling called TIA 568. TIA later merged with EIA and took over the standard. TIA 568 included not only cabling specifications, but also cabling design criteria like network architecture, pathways and spaces and installation guidelines.

The network architecture and nomenclature adopted for TIA 568 was straight from the UTP cabling used for telephone private branch exchanges (PBX)—the private telephone switches used by businesses. The cabling was installed in a star network, and distances were limited to 100 meters, about 300 feet, including connecting patchcords. The 300-foot distance was determined by a 1982 AT&T survey of PBX users.

TIA 568 adopted cabling standards created as part of Anixter’s Levels program with some exceptions. Levels 1 and 2 were not included in the new TIA 568; its lowest performance level was based on Level 3, the cable for 10Base-T, and called “Category 3” to reduce confusion with Anixter’s Levels.

Throughout the 1990s, PC networks and structured cabling grew together but not always in synchronization. As networks got faster, Ethernet moved from 10 Mbps to 100 Mbps, but there was controversy whether to make it run over Cat 3 or require a higher grade of cable. TIA TR42 participants had already created their first high-performance cable, Cat 4, for a new version of IBM’s token ring, but, within months, they also introduced a standard for Cat 5, a 100-megahertz cable that would support a new, simpler version of 100-Mbps Ethernet.

Cat 5 cable was certainly the cable of the ’90s. TIA 568 created a new industry and provided revenue and employment for many during the dot-com era. Buildings were filled with Cat 5 cable to support massive growth in enterprise networks. Even when gigabit Ethernet emerged at the end of the decade, Cat 5 required only a few tweaks and some additional testing (becoming enhanced Cat 5, or Cat 5e) to support 10 times more network bandwidth.

But UTP copper had peaked. At gigabit speeds, it took much more power to send electrical signals over Cat 5e than over fiber. A higher performance UTP design called Cat 6 never gained acceptance. Just a few years later, when 10-gigabit Ethernet was proposed, fiber was easy to implement, but copper struggled. UTP transceivers required more than five times as much power as fiber transceivers, even after “augmented” Cat 6, or Cat 6a, was introduced. It took several more years to get 10-gigabit successfully running on UTP.

Meanwhile, fiber optics was being used for network backbones while copper dominated the desktop. Fiber was an ideal backbone cable, where its longer distance capability made it easier to design large enterprise networks. With the advent of gigabit Ethernet, a new architecture that brought fiber to the desktop, called “centralized fiber” was standardized, but it never gained traction because it required relatively expensive media converters at the desktop.

During all this time, while copper and fiber advocates focused on battling each other, technological developments in mobile devices and wireless networking slipped in. And, well, that’s a tale for next month.

About the Author

Jim Hayes

Fiber Optics Columnist and Contributing Editor
Jim Hayes is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at .

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