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Something old, something new

It is an orderly progression that enables each generation of cabling to support a broader range of applications.


January 1, 2008  


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It has been fascinating to observe the changes in the networking industry over the last 10 years. The global telecommunications network has brought us together in all kinds of weather, at work or at home, to communicate with each other and to share the resources of a rich source of multi-media information.

Network cabling and applications standards, and the industry associations that support these standards, establish the framework and the parameters for building this network. I’ve been personally involved in standards development for over 15 years and it never ceases to amaze me about the progress and the scope of change.

There is a phrase in a poem that I wrote that describes the measured order of change — how much has changed and how much is still the same? That is why the standards for network cabling are so successful and so widely adopted in the industry. They evolve over time, but they build upon a solid foundation.

If we look at network cabling today there are some parameters that have not changed. The cable still contains four balanced pairs with a 100-Ohm impedance, there is a standard 8-position modular connector interface at the equipment outlet, the horizontal cabling distance is a maximum of 100 meters, the equipment is interconnected in a star topology.

All network cabling components are designed to meet a minimum Category of performance for a worst-case channel with up to 4 connectors. The end-to-end channel performance is limited by the Category of the least performing component. Each new generation of cabling is backward compatible and interoperable with previous generations.

What has changed for the new generations of cabling is the transmission performance, which is specified at frequencies up to 500 MHz and the new transmission parameters, such as pair balance and alien crosstalk that are required to support higher speed applications.

The same philosophy of backward compatibility and interoperability governs the subsequent generations of 10 Mb/s, 100 Mb/s, 1 Gb/s and 10 Gb/s Ethernet standards. They are all designed to operate over balanced 4-pair, 100 Ohm cabling over the appropriate Category of performance as specified by TIA (Category 5, 5e, 6 or 6A) or ISO (Class D, E or EA).

They can support the rated speed and also legacy equipment operating at lower speeds using auto-negotiation. It is an orderly progression that enables the cabling to support a broad range of applications, both the old and the new. The cabling that is installed today should be capable of supporting two generations of Ethernet with a minimum lifespan of 10 years.

Another thing that never ceases to amaze me is the innovation that is part of our industry. Ten years ago, the fiber supporters were saying that it was the end of the road for copper at 100 Mb/s.

Here we are today with copper that is still evolving to support network speeds of 10 Gigabit per second and beyond.

To be able to achieve these higher categories of performance requires some innovative enabling technologies. Cabling vendors have risen to challenge. Technologies such as flexible printed circuit board, minimum delay compensation, or multi-stage compensation can be used to extend the frequency response of the mated plug-jack connection up to and beyond 500 MHz. Not bad for a connector that was originally designed for low frequency applications such as ISDN with a specified performance up to 2 MHz.

So what is next? It is interesting to ask the same question that was asked 10 years ago when Category 5 cable was the ubiquitous choice for all new data cabling installations. Is it the end of the road for copper? Based on my own thermometer that I use to gauge the pulse of the industry, I would say that it is not the end of the road but rather a new beginning.

I can sense that there is an excitement about the possibilities of going much farther than we are today to extend the capabilities of copper. Category 6A is good, but is it good enough?

There are things that can be done to improve and to optimize the performance. In a previous article I wrote about the importance of pair balance, which is going to be a key parameter to improve noise immunity. Today this parameter is not adequately specified in the standards.

There are other common mode and mode conversion parameters that are not specified at all. Cabling standards are one or two steps behind technological change and innovation. It never ceases to amaze me. The more we dig deeper, the more we learn. It is an exciting time in the industry — a new threshold and a new beginning.

Paul Kish is Director, Systems and Standards at Belden. The information presented is the author’s view and is not official TIA correspondence