Backbone cabling trends

Q: I am finding a lot of optical-fiber backbone with copper running to the workstations. Is this a growing trend?

Q: I am finding a lot of optical-fiber backbone with copper running to the workstations. Is this a growing trend?

Robert C. McColloch

Riverside, CA

A: Intrabuilding optical-fiber backbone with unshielded twisted-pair (utp) copper cable from the telecommunica-tions closet (TC) to the work area is the norm--the textbook solution for structured cabling. However, many of our clients` requirements are outside the norm--therefore, the "textbooks" are being rewritten.

The first of these rewrites was tele-communications systems bulletin tsb-72, "Centralized Optical Fiber Cabling Guidelines," published in October 1995 by the Telecommunications Industry Association and the Electronic Industries Alliance (tia/eia--Arlington, VA). tsb-72 addresses the requirement of many single-tenant users of high- performance cabling who demanded that data networks be designed with centralized electronics rather than with the electronics distributed throughout the building. Centralized cabling provides connections from the work areas to the centralized crossconnect and is designed as an alternative to locating the horizontal crossconnect in the TC. Although the title mentions only optical-fiber cabling, the bulletin also discusses utp, shielded twisted-pair, and screened twisted-pair centralized cabling.

The next of these rewrites--tia/eia tsb-75, "Additional Horizontal Cabling Practices for Open Offices," published in August 1996--addressed the need for an interconnection in horizontal cabling to allow open office spaces to be reconfigured without disturbing the entire horizontal cable run. This interconnection is called a consolidation point.

If you choose to implement a centralized cabling system and use consolidation points, the schematic of your cabling system looks much the same as the one in the original eia/tia-568 standard. But there is one exception: There are no physical size or environmental requirements for the telecommunications space where your interconnections are located. Consolidation points can be installed in virtually any accessible location, such as above lay-in ceilings and under computer floors.

With such an arrangement, you would expect not to be able to go back later and install a rack of network equipment and interconnections to the work areas. But this might be possible, after all. Just such an idea was proposed by Frank LaPlante of Anixter Inc. (Skokie, IL) at the bicsi Summer Conference in June 1998. He even proposed a new term for the cable from the TC to the network equipment in the work area: horizontal fiber backbone. So what will be the next chink in utp structured cabling`s armor? For my best guess, see "What`s next for structured cabling?"

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