The concept of band-depth

We all know what bandwidth is. Or do we? If we apply a strict definition, "band" refers to operating band, or operating-frequency range

Sep 1st, 2000
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We all know what bandwidth is. Or do we? If we apply a strict definition, "band" refers to operating band, or operating-frequency range. And "width" is straightforward. Literally speaking, to ask how much bandwidth you have is really to ask, "How wide is your operating frequency?"

So, it's impossible to compare the bandwidths of different Category 5 twisted-pair cabling systems, because every Category 5 system has the exact same maximum operating frequency: 100 MHz. And Category 5E offers no more bandwidth than Category 5, because it also operates to a maximum of 100 MHz. Now Category 6 is a different story. Once the standard is ratified, it will specify positive attenuation-to-crosstalk ratio figures to 200 MHz and require system testing to 250 MHz. When we talk about Category 6, it is appropriate to say that the usable bandwidth is (or will be) 200 MHz-twice that of Category 5 and Category 5E. But we all hear the term "bandwidth" used to mean throughput, which is something completely different.

So, if Category 5E does not offer more bandwidth than Category 5, then what does it offer? I say it offers greater band-depth. At 100 MHz, the operating frequency is no wider than it used to be, but you can get more out of it. Better-engineered systems go deeper into the same operating band and get more out of it, resulting in more throughput. They don't make the band wider; they make it deeper. Band-depth.

And how do the engineering minds in our industry maximize the band-depth of twisted-pair cabling systems? Mostly by manipulating the 8-pin modular connectors that quite literally bind these cabling systems together. Certainly, the construction of the cable plays a part, too. But to date, the essence of maximizing the capability of twisted-pair cabling has been minimizing the harmful effects of those plug/jack interfaces.

In this month's Standards feature, John Siemon of the Siemon Co. (Watertown, CT) provides an update on the International Organization for Standardization/International Electrotechnical Commission's (ISO/IEC-Geneva, Switzerland) efforts to establish what amounts to a Category 7 twisted-pair standard. It will have more bandwidth (600 MHz) than any previously specified twisted-pair standard. It will specify a fully shielded twisted-pair medium-proof that the cable construction, not just the connector interface, impacts a system's bandwidth.

But if you look closely at John Siemon's answers to our questions in that feature, you will see the concept of Category 7 band-depth already taking shape. The ISO/IEC's Category 7/Class F standard will specify 600-MHz performance-that's a given bandwidth. But what can be done with that 600 MHz? While it might sound more like a contrived slogan than an off-the-cuff remark, Mr. Siemon's comment about "pushing the reset button" on connector design sufficiently encapsulates his company's efforts to achieve maximum band-depth. The Siemon Co. decided that the traditional 8-pin modular connector is too "shallow" (my words, not theirs) an interface and, therefore, limits a user's ability to mine the depths of the someday-ratified Category 7/Class F performance specifications.

Meanwhile, standards bodies worldwide are inching closer to finalizing a Category 6 specification that will provide 200 MHz of available bandwidth and maintain backward-compatibility with existing 100-MHz-wide systems. As for how deep these 200-MHz systems will be, I suspect they will have the capability to go exactly as deep as the 8-pin modular connector will take them. Whatever that turns out to be.

Patrick McLaughlin

Supplement wins graphic-excellence award

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The cover of the Gigabit Ethernet supplement we published in February 1999 earned a silver award for graphic-design excellence from the American Society of Business Press Editors (ASBPE) earlier this year. The cover shows a man, representative of many cabling-system end users, leaping onto the numeral 1000, symbolizing 1,000 Mbits/sec. Senior illustrator Chris Hipp drew the cover illustration, and the concept incorporated creative input from the magazine's entire editorial and art staff. The cover received the silver award in the ASBPE's East Coast region, in the category that includes buyer's guides, special reports, annuals, and supplements, with circulation less than 80,000.

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