A Matter of Choice

In the quiz (page 76), we ask some questions about choosing voice/data/video (VDV) cabling components for various applications. With so much changing in communications, cabling technology and standards, figuring out which components to use in a particular application can be tricky.

In a large corporate backbone connecting many telecom rooms and thousands of users, supporting Ethernet LANs, wireless access points and VoIP, what is the backbone cable of choice? Certainly it would be fiber optics, as the limited performance of unshielded twisted pair (UTP) copper, even augmented Category 6, along with the bulk of multiple UTP cables, eliminates it from consideration.

But which fiber is preferred? The old standby of 62.5/125 micron multimode (OM1), laser-optimized OM3 50/125 micron multimode or single-mode fiber? The superior performance of laser-optimized 50/125 for networks at gigabit speeds and above makes it the most popular choice for backbones today. But inexpensive single-mode fiber, cheaper than kite string and monofilament fishing line, as one market researcher describes it, makes adding a dozen single-mode fibers to a hybrid backbone cable design a no-brainer.

Suppose a corporate network owner wants to upgrade his electronics from gigabit Ethernet to 10 gigabit Ethernet. He currently has Cat 6 installed. He should first test the installed Cat 6 per TIA TSB-155, a new method of determining the ability of Cat 6 installations to support 10Gbase-T. If the cabling fails, he could install Cat 6A, but at 10 gig, he is going to have to deal with installing a non-standard UTP cable that requires transmitters that cost as much as fiber and use four to eight times as much power, right on the limits of server power capability. It makes much more sense to install laser-optimized 50/125 micron fiber if an upgrade is planned.

What if a company is upgrading its backbone to 10 gigabit Ethernet on laser-optimized 50/125 fiber, but its current backbone is 62.5/125 fiber? It must be concerned about not mixing the two fibers because of the excess loss encountered. There are three things the company should do to distinguish the two multimode fibers:

1. Use the industry-standard aqua color coded fiber jacket on all patchcords.
2. Use LC connectors instead of the current SC or ST styles, especially sensible since most gigabit equipment uses LC connectors on transceivers.
3. Mark all cables and patchpanels with aqua-colored tags.

Finally, consider a new office building for a high-tech company being designed to include a major facility for Internet servers as well as corporate servers and more than 1,500 desktops with 2 PCs each and VoIP phones. This is a good candidate for fiber to the desktop with OM3 laser-optimized fiber. A centralized-fiber cabling architecture eliminates the need for telecom closets, saving the costs of data power and grounds and AC in each closet. A single desktop or clusters of desktops can be served with local fiber to Cat 6 switches or each unit can use a fiber to copper media converter. In a properly designed network, this fiber solution can be less expensive on an as-installed basis. Plus, it allows for future upgrades.

Every application is different, with size and complexity needing to be considered in order to properly choose a cabling solution. For example, if a small business only needs a simple LAN supporting just 100base-T Ethernet, it probably only needs Cat 5e to the desktop. Cat 6, Cat 6A or fiber is overkill for low-speed desktop connections. Small office LANs rarely are physically large enough to need telecom rooms, so every desktop can be directly connected to the server using inexpensive Cat 5e cable.

What about video?

Heightened concern over security has led to an increase in the use of video surveillance cameras. Traditionally, video has been transmitted over coaxial cable unless the distance is too great where fiber is used. Now, a third choice—UTP cabling—is available, a reasonable choice if the monitoring points are within the range of the cabling used for the corporate network. If the camera is just sending video down the cable, using a balun to convert from coax to UTP, it is important to consider the bandwidth capability of the cabling, making Cat 6 a good choice if the distances are long. If the camera has an IP interface, standard network distances will apply.

Another video application is home theater. With digital TV, DVI and HDMI cables are used to connect the TV and media center. In cases where distances are longer than DVI or HDMI standards, optical fiber converters are available at a reasonable price.   EC

is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.JimHayes.com.



About the Author

Jim Hayes

Fiber Optics Columnist and Contributing Editor
Jim Hayes is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.JimHayes.com .

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