The growth of the cabling industry has been well documented over the last 10 years. Two of the major reasons are:

Aesthetics of the structured-cabling system are difficult to quantify. The standards address this issue in passing, with few directions to the end user who employs this system. Are aesthetics really important?

Aesthetics are a component of the system functional performance level, which measures the true performance of a system. System functional performance level (Fig. 2) can be broken down, similar to a three-legged stool, into three interdependent elements:

• The component performance level. It is addressed by standards bodies and manufacturers and is the first line of defense. If a component does not pass specifications, there is nothing that can be done except to replace the faulty component.
  
  
• The installation performance level. This is addressed by BICSI and others. Manufacturers build their components based on certain installation requirements. If the requirements are not met, system integrity can be lost.
  
  
• The aesthetics performance level. This is only lightly touched on in the standards. Aesthetics performance level is the impact that aesthetics has affecting the speed with which faults can be identified and rectified.
  

The 568-A mentions in "Cabling Practices, Telecommunication Closets," section 7.4, and "Equipment," section 8.4: "Appropriate cable routing and dressing fixtures should be used for effective organization and management of the different types of cables in telecommunications closets."

The 11801 addresses this issue in "Connecting Hardware Requirements, Installation Practices," section 9.1.6. "The manner and care with which the cabling is implemented are a significant factor in performance and ease of administration of installed cabling systems."

Below are some examples of typical situations that demonstrate the importance of aesthetics (or the lack thereof):

You have been involved in the installation of a brand-new cabling plant. All the components tested well, and the installation firm did a great job. However, two years later "Frank" moves to another office. You have to patch Frank to his new office. It takes a few minutes to pick out the patch cord in the "rat's nest." Then it takes a few more minutes to search out the appropriate color and length patch cord from the inventory spread across the floor in little piles. After a thorough search, you find that you need a 5-footer and have to use a 7-footer. Rather than order a new cord, you make do. After all, you have 10 more move orders to fill.

The bottleneck to the functional performance level of the entire system in this case is due directly to aesthetics. Extra time (and money) is involved, as well as the cost for mistakes. According to LAN Technology, "Seventy percent of network downtime is cable related." With the industry awareness of the standards and installation practices these days, you can be sure that some of this downtime is due to aesthetics.

Besides affecting the functional performance level, aesthetics can create an impact on the emotional level. This has been detrimental to the industry.

A Fortune 1000 company is relocating its corporate headquarters and is interviewing prospective Systems Integrators to handle its information systems relocation. This includes the design and installation of a structured cabling plant. "Dana," the president of Acme Integration, gives the grand tour of her firm's impressive facilities.

Unfortunately, one of the visitors walks over to the "spaghetti mess" that is Acme's patch-panel system. The rest of the group wanders over, scribbling notes in their notepads. The MIS Director of the Fortune 1000 firm says as he leaves, "We'll give you a call." He never does.

Even in its relative infancy, the cabling industry has been an important discipline that is integral to today's business. Unfortunately, the perception of the cabling industry from the outside is many times one of the "Joe Six-Pack" mentality. Joe Six-Pack is a rather disheveled individual who leaves fingerprints on ceiling tiles and trash in whatever area he was last working in. He is responsible for the "rat's nest" in the company computer room.

The myth of Joe Six-Pack is more than a funny misconception. It is a justification to treat the cabling industry with less respect than other disciplines. Ultimately, it is possible that this "lack of respect" could be translated to a "lack of fair compensation" to the men and women of the cabling industry.

Last year I wrote a piece in this space about 1996 being the "Year of the Installer." That moniker fulfilled itself as BICSI rolled out an impressive Cabling Installation program and TIA/EIA started an Installation Requirements Task Group. It is time for the leaders in the industry, including BICSI, TIA/EIA, ISO/IEC, manufacturers, installers, and end users, to work as a team and make 1997 the "Year of Aesthetics."

How many times have you picked up a trade magazine and seen beautiful advertisements, detailing a full rack of patch panels with every patch-cord management trimming? The patch cords (not too many, of course), plugged into these panels, are routed, oh so elegantly, in the patch-cord management system. They have such a sweeping bend radius, so perfect, looking like someone took a protractor and drew them in place! In bold print you can read the words: "Meets TIA/EIA-568-A or ISO/IEC 11801 bend-radius requirements."

You find yourself saying: "I couldn't get my patch field to look that good if my life depended on it. I must be in clear violation of the standards." Before jumping to conclusions, it is important to review the standards on UTP and ScTP patch cords.

The bend-radius requirements, as stated in the TIA/EIA-568-A standard, section 10.6.3.2 Cabling Practices for UTP (and, by extension, ScTP indicated in 10.2.1) horizontal cable, reads: "Also, in spaces with UTP terminations, cable-bend radii shall not be less than four times the cable diameter for horizontal cable."

This applies to termination on the back of the patch panel (see figure 1) where the horizontal cables terminated and bend-radius stability occurs. There is no bend-radius requirement for patch cords in the TIA/EIA-568-A standard.

In the ISO/IEC 11801, the patch-cord bend radius is included, as set forth in clause 9.1.6-Installation Practices and 8.1 table 15 (line 1.12) mechanical characteristics of 100 ohm and 120 ohm balanced cables: "The minimum bending radius of installed horizontal cable if four ('f.f.s.,' for further study) times the outer cable diameter."

Since there has not been adequate data presented for patch-cord bending radius, the international community has elected to use 'f.f.s.,' which means it is not a requirement for conformance to this standard, only a suggestion.

Now that we have reviewed the standards, let us look at why it would be hard to impose a requirement for patch cords. The primary factor is bend-radius stability, which is the patch-cord radius' resistance to change in its environment, typically dynamic at the patch panel.

Bend-radius stability is predominant at the back of the patch panel (see figure). This is where the four times the outer diameter rule of the horizontal cable applies. Upon initial installation, very few changes are made that could affect bend-radius stability.

At the front of the patch panel, where patch cords are utilized, bend-radius stability does not occur. Typically, the patch field is in a state of flux due to moves, adds, and changes. This state of flux is high considering that the churn rate of companies can be higher than 40% per annum.

While the standards do not address the bend radius of patch cords, neither do they advocate the kinking of patch cords, which can lead to signal degradation in copper and broken glass in fiber patch cords. The subject of bend radius is one of the many topics that will be tackled in the TIA/EIA TR 41.8.1 (authors of 568-A) installation requirements task group, chaired by BICSI's Standards Representative, Donna Ballast, RCDD. This task group was formed to write the installation and design requirements for the future 568-B standard.

If installers or end users have any observations about installation or design that they feel are important, please address them to me and I will bring the request or concern to the task group. Contact Dennis Mazaris, RCDD, PerfectSite Corporation: phone 703-450-2020; Internet address, dmazaris@perfectsite.com.

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.

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).

Figure 1. Patch-Cord Management in the "Real World."

To examine the state of the patch-cord management systems, PerfectSite (Sterling, VA), a structured cabling consulting firm, conducted a study of 20 sites in the Washington, D.C., area during eight months in 1996. To qualify for the study, a site had to have at least 100 unshielded twisted-pair (UTP) or screen twisted-pair (ScTP) modular patch cords attached to a single or adjacent racks or cabinets. The sites included government installations (50%), systems integrators (15%), law firms (15%), accounting firms (15%), accounting firms (10%), and commercial establishments (10%) (see figure 2).

Figure 2. Breakdown of Sites Surveyed by PerfectSite.

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) and tie-wrap devices, used in 41 of the closets, were classified as supplemental to the horizontal and vertical systems with which they were used (see figure 3).

Figure 3. Patch-Cord Management Study.

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:

• Acceptable Slack-The study applied the "three-finger" guideline to determine acceptable slack in the patch cord. That is, the inspector placed three fingers at the point where the patch cord entered the horizontal manager and was routed to the data-equipment port. Acceptable slack of 5 inches or less resulted when the cord could be looped around three fingers at that point. Of the patch cords surveyed, 6% were found to have acceptable slack (see figure 4).
  
  
• Unacceptable Slack-Any length of patch cord over the "three-finger limit" was deemed unacceptable. The study found that 93% of all patch cords examined were too long. The average overage per patch cord was 20 inches. Although this may not seem like much, consider that, multiplied by 187, the average number of patch cords per closet, a total of 312 feet of patch cord, longer than a football field, sits unused in each telecommunications closet. This accumulated slack hangs in disarray, affecting manageability, aesthetics, bend radius, and bend-radius stability (see figure 5).

Figure 4. The Four States of Patch Cords.



Figure 5. Patch-Cord Slack Demonstration.

• Kinked-This condition occurred when a patch cord was collapsed on itself, bent 180°, virtually without bend radius. In every case, kinked patch cords, accounting for 2% of the total examined, also had excessive slack.
  
  
• Banjo-This condition is found between the equipment port and the horizontal patch-panel port when a patch cord that is too short is installed without benefit of vertical management. One percent of the patch cords examined had this problem.
  

"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."

The 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 were four times the outer-cable diameter.

Another issue in this area is bend-radius stability. Unlike the situation in horizontal cable runs, where the cable is stable once installed, patch cords may be moved constantly. A patch cord measured for study on one day may have a different bend radius, or even be kinked, the next day. This situation obviously does not apply to the back of the patch panel, where horizontal cabling can be secured from movement (see figure 6).

Figure 6. No Movement - Terminated Space

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).

Figure 7. Patch-Cord Managers.

The distance between the end of the distribution ring , routing clip, or channel and the patch panel was an important factor affecting bend radius. The shallow depth of the distribution rings, for instance, led to smaller patch-cord bend radius. The shallowest measurement was found, however, on cords directed into routing clips; here depth was typically 0.5 to 1.25 inches. (see figure 8).

If a strain relief or boot was present, the bend might be sharpened even more when directing the patch cord into, say, a 1-inch routing clip (see figure 9). Patch panels from some manufacturers also extended 0.5-inch out from their horizontal plane, further reducing the distance between the distribution ring and patch panel.
	Figure 9. Strain Relief or Boot Contributes to Bend Radius.

Vertical patch-cord management 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.)

Figure 10. Vertical Brackets.

Figure 11. Vertical Bracket.

Figure 12. Vertical Channel.

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 studies used these methods as their sole provider of support. In fact, Velcro 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).

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).

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.

by Dennis Mazaris, RCDD
Dennis Mazaris is a member of the Standards committee of BICSI.

Back in the February BICSI NEWS, I wrote an article concerning bending radius in copper patch cords. Now, it's time to give fiber-optic patch cords the same attention.

Let's look at the typical fiber-optic patch cords specified in the TIA/EIA-568-A and ISO/IEC 11801 used in premises wiring systems today, the 62.5/125 micron, multimode. What do the standards say about the bending of fiber patch cords? Nothing.

"What?" you say to yourself, "You must kidding! Everyone knows if you have a tight bend in a fiber patch cord, you're in for a heap of problems. After all, it's glass."

Let's look first at the TIA/EIA-568-A standard. What does it say about patch cords? Section 12.4.5 addresses the bend radius of fiber-optic cable in the outlet/connector box, not the patch cords. Even in the outlet connector box, it is addressed at 1.18" radius or 2.36" diameter. But, is this even close to being realistic for patch cords, I think not. I suggest that you not take my word on this, but go to your desk and open your top left draw and pull out your handy dandy compass. Yes, the same one you used back in '76 in your high school trig class. Draw a circle of 2.36" diameter on a piece of cardboard. Cut it out and fold it in half, then go over to your patch cords and start "ameasurin'."

Now that you know that fiber in the real world gets bent, quite a bit, let's take a look at how this can affect the patch cord. It is time to introduce the term frequently used in the fiber industry, "statistical anomaly." What does this mean in laymen's terms? For example, you're at a BICSI golf tournament on the 18th tee, 6 strokes in the lead, on a beautiful sunny day. You pull out your Big Bertha driver, tee up, and hit the ball: but, on the follow-through, a lighting bolt strikes your club.

Let's look at the following diagram and chart of "statistical anomaly," and use what you have measured your fiber-optic patch cord's bend radius at, apply this to your fiber life cycle and low and behold, that is your answer.

Although smaller bends in a patch cord may increase attenuation minimally, fiber in a premises is typically bandwidth restrictive not attenuation restrictive.

So, where does this lead us in the standard process for the future TIA/EIA-568 and ISO/IEC 11801 documents. The same place we are with copper patch cords, looking at a real life approach to defining guidelines and rules that can be followed rather than ignored.

If installers or end users have any observations about installation or design (U.S. or International) that they feel are important, please address them to me, I will bring the request or concern to the powers that be at the next BICSI standard committee. Dennis Mazaris, RCDD, PerfectSite Corporation: phone 703/450-2020; e:mail address, dmazaris@perfectsite.com.

We are grateful to BICSI NEWS for permission to reproduce this article, which first appeared in their April 1997 issue.
(Click here to go to the Structured Cabling & Connecting Systems home page.)

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