Megahertz/ megabits

I felt compelled to write concerning the fax-back survey on the need for a Category 6 specification. You will doubtless receive many letters on both sides of the issue, but my concern is not so much the need for a specification as it is that your questions in the survey could be misleading and are illustrative of the technical sloppiness that results in many inappropriate arguments over Category 6.

Steve Zimmel

Manager of Professional

Services Engineering--Domestic

fore Systems

Warrendale, PA

I felt compelled to write concerning the fax-back survey on the need for a Category 6 specification. You will doubtless receive many letters on both sides of the issue, but my concern is not so much the need for a specification as it is that your questions in the survey could be misleading and are illustrative of the technical sloppiness that results in many inappropriate arguments over Category 6.

As someone who is embedded in the Asynchronous Transfer Mode (atm) networking world, I am familiar with the requirements for transmitting data at rates greater than 100 megabits per second, much of atm being focused on 155- and 622-Mbit/sec rates. It is fundamentally important that we distinguish between transmitting data at rates exceeding 100 Mbits/sec and transmitting data at rates requiring fundamental transmission frequencies greater than 100 megahertz. These are very different requirements.

The transmission of 155-Mbit/sec atm, using nrzi (non-return to zero inverted) encoding, or 622-Mbit/sec atm, using cap-64 encoding, requires no more than 78 MHz as the fundamental transmission frequency, well below the 100-MHz limit specified by Category 5. The distinction here must be the transmission frequency, not the data rate.

Data rates may or may not be in a 1:1 correspondence to transmission frequency. The rampant ignorance about this fact is what allows the marketeers to create fear, uncertainty, and doubt in the minds of many, and to fuel the majority of the Category 6 rhetoric. Please point out to your readers that 100-Mbit/sec data rates can require different fundamental transmission frequencies, depending on the encoding scheme. The trade press and cable manufacturers must not be allowed to interchange data rate and frequency for the purpose of exploiting customer ignorance.

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