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Note: The following technical article was current at the time it was published. However, due to changing technologies and standards updates, some of the information contained in this article may no longer be accurate or up to date.

Reprinted with permission from FIBEROPTIC PRODUCT NEWS.

Fiber Survivability: Protecting The Passives

By Lou Maiolo for The Siemon Company

Often overlooked, the protection of fiber optic patchcords is essential to the survival of the network. A kink or severe bend in a fiber optic patchcord can result in unacceptable attenuation and eventually a lost signal. Lost signals equate to lost revenue. One of the Long Distance Companies shared the information listed in Table #1 with me. This table tells us that a typical "transaction" (e.g. conversation) requires 56,000 bits. The Long Distance Provider claimed that his company's typical transmission is 2.5 Gigabit. This equates to approximately 45,000 transactions per minute. Add in transmission using an 8 channel WDM and now we are transmitting 360,000 transactions per minute. Using $0.20 per minute as a revenue rate, this translates to $72,000 per minute in potential lost revenue when a signal is lost!

56,000 Bits per transaction
2.5 Gig typical transaction today
= approx 45,000 transactions per wavelength
w/8 channel WDM = 360,000 transactions
@ $0.20 per minute

Table 1

So how do you protect your fibers? Before routing any patchcords, strongly consider a Fiber Protection System (FPS) for housing these patchcords. A properly designed (and installed) FPS will protect your fiber network by ensuring that proper fiber bend radius is maintained. A proper FPS will also provide for accessibility to your fiber cables now, and in the future as you expand the network.

Here are some helpful tips on FPS selection and use:

Protect Your Fiber: Don't latch it to ladder racking, it may attenuate.

Methods and procedures followed for coax or copper cables just don't apply to fiber optic cables. Coax and copper cables typically won't attenuate when latched to ladder racking (figure #1). Fiber Optic cables, however, are delicate. Latching can squeeze the fiber inside creating macro bends resulting in light loss and signal degradation.

Figure 1: Don't latch fibers to ladder racking.

Protect Your Fiber: Don't lay it on top of the racks, you may need to get to it.

Fiber Cables are indeed delicate. Weaving your way through a "spaghetti bowl" of tangled fiber optic cables is surely one way to break a fiber. Part of protecting the fiber cables involves making them accessible. When fiber protection systems (FPS) or ducting is used (which should be always), it should be installed low enough from the ceiling to permit accessibility inside. In figure #2, the FPS has been placed up against the ceiling making accessibility difficult. Additionally, this user has selected an FPS which has "fingers" in lieu of solid walls. A lazy or uneducated installer has used the finger retainers as a means to coil storage loops. As these "fingers" have no radius control for the fiber cables, attenuation is sure to occur, if it hasn't already.

Figure 2: Don't lay duct on top of frames.

Durability: Play it safe, go for the strong stuff.

All too often, price is the governing factor when selecting a FPS. Some FPSs are cheaply priced, but just aren't durable enough to hold the weight typical of large central office fiber deployment. The last thing that you want to happen is buying a cheaper FPS that sags under load from fiber patchcords. A durable 8' wide FPS (the ideal size for large central office applications with a capacity of 2400 patchcords) should be able to hold over 50 pounds over a 6 foot span without sagging (figure #3)*. Before selecting a FPS, estimate the number of fiber patchcords that you will be installing at the site when at full capacity. Next, ask your FPS supplier for a chart showing patchcord capacity and weight capacity by FPS size.

*An 8"W x 4"H FPS can hold 2400 patchcords at full capacity. 2400 patchcords at 10 grams per patchcord = 24 kgms or 52.8 pounds (1 Kgm = 2.2 lbs.)

Figure 3: Lightways™ 20-foot span at City
of Anaheim Central Office; note no sagging.


Figure 4

Ease of Assembly:Keep it simple.

When selecting a FPS, calculate total installed cost rather than just the cost of materials. You may find that some low material cost FPSs will cost more in the long run after installation labor is factored into the equation. Hardware-laden FPSs can take over 50 hours to install for a typical 20' x 20' square horizontal run with a dozen vertical drops. This same installation could be accomplished in less than 24 hours with a snap-together system such as the LightWays&153 FPS offered by The Siemon Company (figure #5). This labor savings could amount to thousands of dollars for this particular example. Always calculate total installed cost (material and labor) rather than just material cost.

Figure 5: LightWays™ snap-together system.

Ease of Use: Let me get to everything

Most FPS systems recommend the use of tubing to protect and route fiber cables in the horizontal to vertical transition. These flexible tubes may not be a problem initially when fiber patchcords are threaded through them. But adding patchcords at a later date can be difficult as these tubes can be clogged and congested. Threading patchcords through these tubes can cause unwanted strain on fiber connectors and, in some cases, cause fiber breakage. In some installations that we visited, tubes had become so congested that patchcords making horizontal to vertical transitions actually bypassed the tubes, hanging in the air unprotected (figure #6). An "open channel" system, where patchcords can be layed into the FPS rather than threaded through tubing, does a much better job of providing accessibility to patchcords installed in the FPS, and of accommodating future growth (figure #7).

Figure 6: Congested tubing results in "free-falling" fibers.

Figure 7: LightWays™ "open channel" system.

Ease of Expansion: Make it fast, make it simple.

One of the most dangerous procedures can be to add another horizontal path (tee) or vertical drop to an existing FPS which has patchcords already installed inside. Most FPSs require (1) elevating (moving) "live" fiber cables so that an FPS section can be removed (cut out with a saw) and (3) a horizontal tee or vertical downspout can be fastened to the existing structure with hardware. These three steps must be handled with extreme care, especially when moving "live" fibers. Frequently, this operation must be conducted on "off-peak" hours (eg. 12 midnight - 6:00AM) so as to minimize revenue loss/customer inconvenience should a fiber break or disconnection occur. Installer time can be expensive and difficult to contract at these off-peak hours.

Figure 8: LightWays™ ramp provides bend radius
protection. LightWays™ vertical drops snap in place.

The Siemon Company's LightWays™ FPS offers a simple alternative method of expansion whereby "live" fibers need not be moved, and no assembly or disassembly of hardware is required. A unique cut-out tool removes a section of the FPS wall precisely where the horizontal expansion or vertical drop is to be added (figure #9). A breakout kit or vertical drop kit is then snapped into place, requiring no hardware (figure #8). Expansion of the original FPS is performed safer, and much faster (less than 5 minutes total) than other FPS systems.

Figure 9: LightWays™ cut-out tool makes
vertical drops safe, simple and quick.

Go back and fix it: Retrofits.

What if you've already routed your fiber cables horizontally and vertically, using ladder racking as a means of cable support…or…you have unfortunately selected a cheap FPS that now sags from patchcord weight? Or, what if your FPS is filled to capacity with no room for future growth? Now you can do something about it. The Siemon Company's new LightWays&153 FPS has "retrofit" parts (figure #10) that have slots built into them so that during installation, patchcords can pass through these slots into the FPS without the inconvenience of disconnecting the patchcords and experiencing service interruption.

Figure 10: LightWays™ retro parts have a
slot for routing existing patchcords without
the need to disconnect circuits.

Ease of Ordering: Get it all.

Will somebody please offer a software program that helps users layout an FPS system in a common format like VISIO? How about a software program that generates a bill of materials to expedite the ordering process? Now somebody finally has. The Siemon Company has developed a software program for it's new LightWays&153 FPS that allows the user to create a top down and side view FPS layout/drawing AND also provides a bill of materials to expedite the ordering process (figure #11).

Figure 11: LightWays™ software
assists in the ducting layout.

Conclusion:

Fiber is revenue. Fiber is delicate. Protect your fiber. Use a FPS to route and protect your patchcords as they run from the splice center to patch panels to equipment. Select a FPS that offers the lowest total installed cost. Labor can be expensive with hardware-laden systems. Choose a durable system that is easy to work with (open channel concept), and simple and safe to expand.

Author:

Lou Maiolo is President of Maiolo Associates, A consulting firm based in Long Island New York, which performs consulting services for The Siemon Company.


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