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In glossy brochures and trade show displays, patch panels are always tidy and well-dressed. In the telecommunications closet, however, the reality more closely resembles a "rat's nest" - a term that is frequently used to describe this area .Dennis Mazaris, PerfectSite As the demand for high-speed enterprise networks has increased, so has the need for high-density modular patch panels and the patch cords that populate them. And with the limited space available in wiring closets and equipment rooms, the need for patch-cord management systems is greater still. While cabling standards such as TIA/EIA-568A and the international standard ISO/IEC-11801 have addressed many cabling issues, they pay little attention to the most disorganized part of any cabling infrastructure: the patch-cord management system. Often described by such terms as "rat's nest," "spaghetti," and "jungle," the working patch panel is both an eyesore to visitors and an invitation to networking problems for installers and maintainers (see figure 1). |
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During the study, the PerfectSite inspection team examined 473 patch panels in 87 wiring closets. In all, 16,242 patch cords were inspected, along with 723 horizontal patch-cord managers and 1066 vertical managers. Hook-and-loop (or Velcro(r)) and tie-wrap devices, used in 41 of the closets, were classified as to the horizontal and vertical systems with which they were used (see figure 3). | |||||||||
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The study consisted of random selection and examination of the 1624 patch cords, 10% of the total, for a statistical accuracy level of ±3%. | |||||||||
The examinations conducted by the inspection team showed that the patch cords-which, for the purpose of the study, were defined as flexible cables with modular plugs on each end that are used to establish connections between patch panels and equipment-could be divided into four categories, as follows: | |||||||||
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"The number-one problem in patch-cord management today is excessive slack," says Herbert Mendelsohn, a retired communication specialist, formerly with the U.S. Department of Agriculture and now an industry advisor. The problem occurs because patch cords are manufactured in one-foot increments rather than to length. Moreover, when companies stock many different lengths in inventory, they commonly use an overly long cable when the correct length is out of stock. Also, when in doubt, cable-plant managers typically order cords that are too long, since cables that are too short are virtually useless. "Another problem," adds Mendelsohn, "is something I call 'the entangling effect.' This phenomenon occurs when someone relocates a patch cord and, instead of pulling it out completely and starting over, he or she simply unplugs the patch cord and sticks it into the new port atop the other cables." Other findingsThe PerfectSite study also shed light on a number of other patch-cord issues. For example, should you rely on manufactured patch cords or make your own? Only 3 of the 20 sites surveyed made their own, while 85% depended on manufactured patch cords. Manufactured cords were preferred because they were thought to be more reliable, and even those sites that made their own were discontinuing the practice because of the high data rates the cords were expected to carry, the lack of experienced labor to make them, and the unmet need for quality assurance. Ironically, hand-made cords generally had the same amount of slack as manufactured patch cords. At the time of first use they may have been cut to exact length, but over time these cords were moved around and so the advantage of custom fit was lost. Another area of concern has been bend radius. Many industry practitioners mistakenly apply Section 10.6.3.2 of TIA/EIA-568A to patch cables. The standard calls for a bend-radius of "not less than four times the cable diameter for horizontal (UTP) cable," and by extension the same limit is applied to ScTP cable in Section 10.2.1. However, this restriction only applies to the termination of horizontal cable runs at the back of the patch panel, and not to the patch cords found at the front. In the international standard, the patch cord is included in the bend-radius requirement set forth in Section 9.1.6-four times the diameter of the outer cable. However, the requirement is marked "f.f.s." (for further study), which means that it is not required for conformance to the ISO/IEC 11801 standard, since adequate data has not been presented to the scientific community. Only 7% of the patch cords surveyed by PerfectSite had bend radiuses four times the outer-cable diameter. |
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Patch-cord management
Horizontal and vertical patch-cord management systems also affect bend radius. For example, the study found three types of horizontal patch-cord management in use, each of which affected bend radius differently. Distribution rings were the most common way of directing the patch cords from the patch panel to the vertical management system. Routing clips were used at some sites. Smaller than distribution rings, they could be more densely populated on the horizontal manager, allowing a straighter patch. The third type of horizontal manager was the channel or duct (see figure 7). |
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A vertical patch-cord management system usually consisted of either brackets or channels. The brackets came in many sizes and shapes (see figure 10), but were often comparable in size to their horizontal counterparts, even though required to handle many more cables (see figure 11). Channels, because they are more restrictive, showed by far the most problems when it came to bend radius and cable slack (see figure 12). (Cabinets also exhibited more problems than racks with bracket managers for the same reason: Their restrictiveness lowered bend radius and made slack more difficult to deal with.) | |||||||||
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Vertical management systems were clearly more problematic than horizontal ones. The PerfectSite study showed that many vertical management systems were simply incapable of accommodating the amount of cable slack accumulated in the patching system. However, bend-radius problems were not as prevalent as those encountered in horizontal management systems, although 32 cases of kinking were recorded. This was because of the great accumulation of slack that had built up over time in vertical systems, along with the entangling effect described above. Also, vertical systems were more likely to have patch cords tightly crammed into them, creating a situation best described as "overfilling." Supplemental support from the hook-and-loop or cable-tie systems has improved substantially over the last two years, but none of the sites studied used these methods as their sole provider of support. In fact, Velcro(r) strips or plastic tie wrappers were more often used in desperation just to keep patch cords out of the way. In each case where such devices were employed, it took longer to identify a patch cord because it was first necessary to remove the Velcro strip or tie wrap (see figure 13). |
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Some possible remedies
The Perfect Site study indicates that high-density patching using conventional patch cords and panels is inadequate for the demands of a commercial environment, even though the sites surveyed had ample horizontal and vertical patch-cord management systems. In almost every case, these installations violated the spirit, if not the letter, of applicable national and international standards. For example, Section 8.4 of TIA/EIA-568A states: "Appropriate cable routing and dressing fixtures should be used for effective organization and management of the different types of cables in telecommunications closets." ISO-IEC-11801, in Section 9.1.6, provides similar guidance: "The manner and care with which the cabling is implemented are significant factors in performance and ease of administration of installed cabling systems." The problems with patch-cord management today-the accumulation of excessive slack in standard-length manufactured cords and the entangling effect that turns them into "spaghetti" over time-will not be solved by handmade patch cords. As we have seen, such cords may eventually experience the same problems as manufactured items, and they suffer the additional problem of uncertain, inconsistent, or degraded performance. This has lead patch-cord users to cast about for other solutions to these problems. One alternative that some firms are using is to terminate one end of the patch cord on a punchdown block, while the other end is terminated in the traditional way, with a connector that fits into the equipment (concentrator). The patch cord punchdown block connects to the horizontal cabling system through a crossconnect field. Creating such a crossconnect field permits you to cut your patch cords to the proper length for each connection (see figure 16). |
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However, such a solution may be in violation of TIA/EIA-568A if the manufacturer's punchdown block does not accept stranded cable. The cabling standard currently calls for using stranded patch cords in this application, although solid-wire patch cords are being examined for possible inclusion in an addendum to the standard. What is certain is that the patch-cord problem is real, and it is important. According to Datapro Information Services Group, "Physical management problems account for 50% of network problems and downtime." At least some, and perhaps much, of this downtime results form problems with patch cords. Why don't such problems get addressed? A recent survey suggests an answer to this question. Several years ago, Computerworld magazine surveyed 361 information-systems professionals and generated a list of the Top 10 Worst Jobs in Information Systems. Second on their list was troubleshooting cabling. "It is an especially frustrating and time-consuming task," the article said.
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Dennis Mazaris, registered communications distribution designer (RCDD), is president of PerfectSite (Sterling, VA), a cabling consultancy devoted to needs analysis and design, third-party verification, performance monitoring, mediation, bid-package evaluation, market analysis, and training. | |||||||||
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