To the EDITOR

Mohawk has been supporting an open-system solution for more than 10 years. We see this as one of our strengths, as well as a strength of the industry as a whole.

Open systems

Mohawk has been supporting an open-system solution for more than 10 years. We see this as one of our strengths, as well as a strength of the industry as a whole. If the TIA/EIA-568-B standards mean anything, then an open system should be able to stand on its own merits against any closed system. And from my experience, they do.


Editor's note: Due to an editing error, the article "A new focus on end-to-end solutions" in our December 2004 issue failed to list Mohawk as one of the companies with which The Siemon Co. Shares a warranted solution.

Mohawk endorses and supports the TIA/EIA-568-B standard, which recognizes and approves an open-architecture cabling system. The following is excerpted from TIA/EIA-568-B.1 Commercial Building Telecommunications Cabling Standard - Part 1: General Requirements:

• Notice (From inside front cover of document): "TIA/EIA Engineering Standards and Publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvements of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need."

• 1 Introduction - 1.1 Purpose: "This Standard specifies a generic cabling system for commercial buildings that will support a multi-product, multi-vendor environment. ... This Standard establishes performance and technical criteria for various cable system configurations for accessing and connecting their respective elements. In order to determine the requirements of a generic cabling system, performance requirements for various telecommunications services were considered."

From the opening Notice of the document, the word "interchangeability" says it all. This train of thought is continued in the Introduction references of "support a multi-product, multi-vendor environment"; in essence, open architecture. A multi-product, multi-vendor environment, as stated above, allows the purchaser a wider opportunity for cost-effective and compliant solutions.

The open-system approach allows the consultant, end user, and contractor greater flexibility in deciding what products and which vendors best suit their needs.

Mohawk's Category products not only meet, but exceed the requirements of 568-B, with performance and compliance independently verified by ETL. For Mohawk to state that our products meet the TIA/EIA Category 6 requirements, they must be independently verified to meet all requirements across the entire frequency range. We also have independent testing of our products with multiple connectivity vendors to ensure both permanent-link and channel performance.

Additionally, Mohawk has end-to-end copper and fiber proprietary warranty solutions with Hubbell (SureBit), Leviton (NetSync), and Siemon. We also partner in the open-architecture arena with Molex, Ortronics, and Panduit, to name a few.
Greg Niemiera
Mohawk
www.mohawk-cable.com

Brian Milligan's excellent article ("A new focus on end-to-end solutions,") is quite accurate in assessing that the renewed trend to "closed" end-to-end solutions is causing a stir in the marketplace. Many in the industry were quoted for their predictions as to where these new alliances will lead. While none of us has a crystal ball, I would like to offer additional commentary to some of the issues raised.

It was claimed that a "closed" end-to-end solution will inspire confidence from the end user, and any potential problems can be more easily addressed. I cannot speak for all connectivity hardware manufacturers, but our connectivity products carry a lifetime warranty, and our certified warranty program supports an open-architecture solution where we are the sole point of contact for the customer.

We do not require our certified contractor partners to "commit" to hundreds of thousands of dollars, and we recognize we have an equal contribution with them to assure a quality installation. We understand the challenges our distributor partners have in managing their inventory assets, and work with them to determine minimum inventory levels that support the needs of the marketplace, not the wishes of the manufacturer. We believe and participate in the development of ANSI/TIA/EIA and ISO international generic cabling standards, and are thankful for the work of independent testing labs such as ETL and UL that validate the quality of manufacturers' products in reference to those standards. Most important, we believe that end users, specifiers, and installers make informed decisions for their cabling and connectivity infrastructure based on sound performance criteria, not marketing hype.

Is a manufacturer that private-labels a premium (only) 5e cable going to support a minimally compliant [Category] 5e cable solution? Will they have all necessary colors in plenum and PVC? If not, aren't you dealing with more than one company anyway? What about augmented Category 6 cable? What if they do not private-label optical-fiber cabling? Who do you contact? Are they prepared to show unaltered, independent testing data for comparison to open-architecture solutions? If not, are you being asked to pay a premium for an installation that may be less robust? These are just a few of the questions "closed" end-to-end solutions raise.

Time will tell if the "closed" end-to-end solutions are what the market wants; however, typically customers are looking for more quality options, not fewer. We will continue to promote a connectivity-hardware solution based upon performance and value that supports an open-architecture environment, for we believe that is what the market wants: more options, not limitations.
David Levine, RCDD
National sales manager, network cabling solutions
HellermannTyton
www.hellermann.tyton.com

Shielded from facts?

I was glad to see Betsy Ziobron's article on shielded cable ("Shielded twisted-pair boasts EMI fighting qualities") in the December issue of Cabling Installation & Maintenance. In vain, I searched the article, as I have searched other similar articles, for the quantitative data that should be included in discussions on EMI. There is no question that shielded cable will limit EMI better than non-shielded cable. The question in our mind: Is it really necessary?

Have there been documented studies showing that EMI levels found in the "typical office" do indeed cause data-transmission problems over UTP? We have taken lengths of Category 6 cables and tightly wrapped multiple loops around fluorescent ballasts and observed signal responses on an oscilloscope, only to find no discernable changes in the scope traces. Granted, this demonstration was not rigorous science, but it raised the question with us: How much EMI is too much?

Seems like the industry needs a dose of scientific research as well as antidotal evidence. Thanks for the article, and keep pushing the industry to produce the science to back up the claims for the need.
Bruce B. Turner, RCDD
NAC Engineering/Northwest Architectural Company
www.nwarchco.com

Word problems

After reading your editorial column ("Word problems," November 2004), I would like to point out some inaccuracies. ACR is the ratio of attenuation and crosstalk, measured in dB at a given frequency. The term "ratio" comes from the fact that it is the quotient between attenuation (power loss) and crosstalk (unwanted signal transfer from adjacent pairs). Once you take the logarithm, the ratio becomes a difference. The same applies to SNR-signal-to-noise ratio; it is a ratio of signal power and noise power, but when expressed as a log it becomes a difference.
Ermanno Pietrosemoli
Latin American Networking School
www.eslared.org.ve

An interesting editorial, but I disagree with your dissertation on ratios. Perhaps an electronics, rather than a plain English, dictionary is required. "Signal to noise," "attenuation to crosstalk," and any other measurement expressed in decibels (dB), decibels referenced to milliwatt (dBm), or any other such "db_" unit(s), are indeed ratios.

These measurements are the logarithms of the ratio of one power level to another. I don't recall the exact mathematics, but as a student, I did have the same question as you-namely, how is this a ratio? At that time, when I finally grasped the entire concepts regarding signal strength, noise levels, attenuation, crosstalk, etc., I also learned that a ratio was, in fact, most appropriate.

As far as ACR is concerned, I do believe that signal strength is measured on an inverse scale with noise. For example,0.0 dBm of signal is equal to 90 dBrn of noise, and -90 dBm of signal would be equal to 0.0 dBrn of noise. Also, each 3dB of attenuation is equivalent to a 50% reduction of signal strength, because of the fact that we are dealing with logarithms.

It has been a long time since I needed to do these calculations, as modern test equipment seems to do it all for you. But I do believe that these ratios you contest are, in fact, just that.
Rich L.
Via e-mail


Editor's note: Now that Rich mentions it, I do remember that a 3-dB increase in attenuation halves a signal's strength. With that in mind, I should have known I was in over my head technically while ranting and raving about ACR. I guess I also could have benefited from taking more math classes and fewer British literature classes in school. William Blake's "Songs of Innocence" and "Songs of Experience" never have helped me examine the cabling industry, but a better understanding of loarithms and decibels most assuredly would.

I, too, have always felt that attenuation-to-crosstalk ratio is dumb and meaningless. It probably was thought up by some vendor's marketing department; however, signal-to-noise ratio (SNR) is a valid concept, although what we're usually measuring is (Signal Power + Noise Power)/(Noise Power), or (S+N)/N. In most cases, N is much smaller than S, so we ignore it in the numerator.

SNR is valid when both the signal and noise levels are in the same power units, such as watts, milliwatts, or microwatts. The SNR is a dimensionless ratio but can be converted to decibels (dB) by taking 10log[S/N]. Alternately, each quantity can be converted to dB with respect to some common reference, such as dBm (1 milliwatt reference) or dBw (1 watt reference), and then the difference taken to find SNR(dB). In the case of dBm, SNR(dB) = S(dBm) - N(dBm).

Regarding "NIC card," here's another that will probably bother you: LCD display-liquid crystal display display.

By the way, the so-called "certification" you refer to is another concept invented by marketing departments to try to differentiate their products from their competitors'. It always surprises me how many people fall for this silly nonsense, which of course is why the marketing departments use it.
Whitham D. Reeve, P.E.
Reeve Engineers
www.reeve.com

Recycling cable

Both the "Ask Donna" and the editorial columns in your September 2004 issue reference recycling cable. Our company, Joseph Krash Metals, in Bedford Heights, OH is a processor of insulated cable. We buy any and all types of copper wire, and shred and chop it to the point where all that is left is pure copper, which we recycle directly back to the rod mills who remelt it into new rod for redrawing into wire again.

We have worked with many distributors and installers over the past year and have paid out millions of dollars to these companies for the cable they took out of AT&T, SBC, and other companies when they were replacing it with new materials. Occasionally, scrap wire gets overlooked by a contractor, or stolen by subcontractors. But if a system is put in place in which we work with the installation company, profit margins on the jobs do increase. In some cases, a misquoted job that would have shown a loss turned into a profit once we paid for the scrap.
Tom Catanzarite
Joseph Krash Metals
e-mail: jkrashmetals@hotmail.com

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