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A Tutorial on Centralized Optical Fiber Cabling Networks Part II

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ATutorialonCentralizedCentralizedOpticalFiberCablingNetworks PartIIby Douglas E. Harshbarger and George Sellardn the conventional, decentral- of distributed electronics. Howev- dated in the main cross-connect,ized premises data network, er, telecommunications closets take the centralized design is a vehicleFIBERI backbone cables travel from a up valuable real estate and, because for reducing the number ofOPTICS main cross-connect (or, in an inter- of the active electronics, they telecommunications closets. Thebuilding network, an intermediate require power, air-conditioning long cabling runs typical of thesecross-connect) to one or more hor- and grounding. Decentralization designs, often exceeding 100 m, areizontal cross-connects (HC) in increases complexity and presents perfect for fiber, but impractical fortelecommunications closets on multiple potential points of failure. copper.each floor of a building. The HC Moreover, the use of UTP copper A variation on the centralizedtypically includes active electronics cable in the conventional design design is the multiuser outlet net-equipment like hubs, concentrators places bandwidth limitations on work. From the telecommunica-or switches. Individual outlets for the network. And because of its tions closet, a high-fiber-counteach user are located within 100 m inherent electrical properties, UTP cable travels to a multiuser outletof the telecommunications closet is vulnerable to electromagnetic which ...
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ATutorial on Centralized Optical Fiber Cabling Networks PartII
n the conventional, decentral-ized premises data network, OPTICSmIain cross-connect (or, in an inter-FIBERbackbone cables travel from a building network, an intermediate cross-connect) to one or more hor-izontal cross-connects (HC) in telecommunications closets on each floor of a building.The HC typically includes active electronics equipment like hubs, concentrators or switches.Individual outlets for each user are located within 100 m of the telecommunications closet (TC) and are connected to the HC using a single cable per user in a physical star configuration. In the conventional design, most inter- and intra-building backbone cable is optical fiber. The horizontal segment of the network typically is comprised of unshielded twisted pair (UTP) copper cable. The trans-mission distance limitations inher-ent in copper cabling make distributed design a necessity, in that using copper in the horizontal network requires that data elec-tronics be located no more than 100 m from workstations. The traditional cabling infrastruc-ture was designed to provide maxi-mum flexibility in the deployment
PAGE 68CBM OCTOBER1998
by Douglas E. Harshbarger and George Sellard
of distributed electronics.Howev-er, telecommunications closets take up valuable real estate and, because of the active electronics, they require power, air-conditioning and grounding. Decentralization increases complexity and presents multiple potential points of failure. Moreover, the use of UTP copper cable in the conventional design places bandwidth limitations on the network.And because of its inherent electrical properties, UTP is vulnerable to electromagnetic interference (EMI), radio frequency interference (RFI), crosstalk and breaches in data security.That is, copper is fairly easy to tap. Today, after years of the decen-tralized network’s popularity, man-agers are turning to a more elegant, efficient and cost-effective design: the optical fiber centralized net-work. Thecentralized design pro-vides direct connections between up to 200 workstations and a single main cross-connect (MC) by using pull-through cables or a splice or interconnect in the telecommuni-cations closet. With network electronics, analyz-ers, uninterruptible power sources, cross-connects and servers consoli-
dated in the main cross-connect, the centralized design is a vehicle for reducing the number of telecommunications closets.The long cabling runs typical of these designs, often exceeding 100 m, are perfect for fiber, but impractical for copper. A variation on the centralized design is the multiuser outlet net-work. Fromthe telecommunica-tions closet, a high-fiber-count cable travels to a multiuser outlet which is affixed to a permanent structure, such as a column.Each multiuser outlet can support any-where from six to 12 offices.Opti-cal fiber patch cords are installed through furniture raceways to indi-vidual work area outlets. The multi-user design allows for office reconfigurations without disrupt-ing or relocating horizontal cabling. Benefits of the Optical Fiber Centralized Network Any fiber-to-the-desktop design offers significant networking advan-tages. Mostimportantly, an all-fiber cabling infrastructure provides very high bandwidth, which has become critical for organizations that require bandwidth-hungry applica-
tions such as those for graphics, multime-dia and real-time video.An optical fiber centralized network is future-proofed against growing bandwidth demands from users. Also, the fiber infrastructure is protocol-independent and able to accom-modate all current and future transmis-sion protocols such as FDDI (fiber distributed data interface), asynchronous transfer mode (ATM), Gigabit Ethernet, 100BASE-FX, 100VG-AnyLAN and Fibre Channel with no disruptive and expen-sive recabling.Finally, optical fiber’s immunity to EMI/RFI (electromagnetic interference/radio frequency interfer-ence) impedance mismatches and ground loops improves link performance and vir-tually eliminates maintenance. In addition to these performance advan-tages, the optical fiber centralized design offers numerous cost-saving benefits.With direct connections between network hardware and desktops, maintenance and network management are simplified. There is less electronic equipment to maintain in fewer locations, thus reducing downtime and maintenance costs.Also, network reconfiguration is simplified.A network manager can establish work-group networks very quickly because all cables terminate in a single location. The centralized design also is cost-effective because it eliminates the need for multiple telecommunications closets with active electronics, which require power and air-conditioning, as well as devices for fire detection and security. Keep in mind that the average cost of owning a single telecommunications clos-et—excluding the costs of labor, power, and cooling—is approximately $355 per square foot (Source:Gartner Group). Eliminating the costs associated with housing multiple telecommunications closets in a network translates into con-siderable initial savings.For example, Sel-lard designed an optical fiber centralized network for an Erwin, N.Y., manufacturing facility, a part of Corning Inc.At the Erwin plant, four telecommunications closets, which were required for the previous net-work, were replaced with one closet using the centralized design.The result-ing savings in initial costs amounted to approximately $24,000 per closet.In another centralized design at the Getty Museum in Los Angeles, 55 closets were replaced with one, at a savings of $73,000 per closet. These numbers are significant, especially when you consider that approximately 45 percent of corporations have three or more telecommunications closets per floor (Source:Digital Equip-
ment Corporation). The centralized design also is an attrac-tive option when cabling or recabling existing buildings where closets either do not exist or are not suitable for active net-work hardware.In these situations, run-ning optical fiber from the main cross-connect directly to workstations often is the most cost-effective installation method. Another benefit of the optical fiber centralized design is improved port and chassis utilization.Centralizing all elec-tronics in the main cross-connect reduces the number of ports and chassis required by a network, resulting in cost savings. Onaverage, only 70 percent of hub ports are used in the conventional decentralized design, due to the varying number of users per telecommunications closet. Thecentralized design is much more efficient. Typically, hub port usage is 90 percent in a centralized design. That 20 percent differential represents real and immediate savings. Centralized Networks Are Key to Future Success Finally, centralized networks may form the basis for yet another paradigm shift in private networking. A current trend is for organizations to employ native LAN (local area network) services to consolidate far-CBM flung networks into virtual private net-works (VPNs) managed from outside by service providers.This development promises to speed the convergence of voice and data on a single, seamless, high bandwidth network. As services and infrastructure continue this consolidation, optical fiber will play a key role. With data and voice traffic consol-idated on the same network, all information
In the traditional cabling design, cables run to active telecommunications closets located within 328 feet of users. Eachcloset contains active network electronics. Therefore, the space requires power, air-conditioning and grounding.Category 5 copper cables connect closets to users.
HUB HUB HUB HUB HUB HUB HUB HUB HUB
will travel over fiber between locations. Extending fiber within locations all the way to the desktop over centralized networks will simplify maintenance, help avoid band-width bottlenecks and save money. Donald E.Harshbarger, RCDD, is mar-ket development engineering manager, premises systems, for Corning Inc. George Sellard is president of Sellard Communications. Specialthanks to Patrick Scanlon of Rochester Institute of Technology for his assistance.
In the centralized design, optical fiber to the desktop is achieved with direct connections between a single hub and each user by using pull-through cables or a splice or interconnect.An alternative centralized design features high-fiber-count cables and multiuser outlets.
Interconnect or Splice
Pull-through Cable
MC MC Centralized Cabling DesignMultiuser Outlet
OCTOBER 1998CBM PAGE69
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