Installation Options : Air Blown Fiber

C onventional methodology used in designing and building optical fiber LAN infrastructures is ill-equipped to deliver the flexibility to accommodate ongoing adds, moves, and changes caused by advances in information technology and evolution within the organization. The more dynamic the organization, the more the organization must spend to keep its LAN capabilities current with user demands. The bulk of these costs are associated with labor-intensive pulling and splicing of new cable to handle, for example, multimedia, to change the location of a network hub, or to relocate a department within the organization. Additional costs can be traced to downtime or disruptions in the workplace during cable-pulling operations. LAN managers have attempted to reduce future costs by installing more fiber than required at the outset, thereby hoping to capitalize on a “one-time” installation procedure. They do this by crystal-balling future needs, hopingtheir guesswork proves correct. More often than not, it proves wrong, and the anticipated savings do not materialize. A relatively new LAN infrastructure technology called air blown fiber (ABF) can solve this problem. One of the first applications in the United States was at the University of Utah. Since then, the technology has proven itself, and is being adopted by a wide range of businesses and institutions (see Applications) to "future proof' their networks. In addition to handling voice, data. and video LAN traffic, ABF is also employed for HVAC and security systems. ABF blowing equipment consists of bottles of air or dry nitrogen fed through tubing into the air blowing system. An air-driven motor in the blowing head controls the speed at which fiber travels into the tube cells ABF tube cables, containing up to 19 individual tube cells, are interconnected in tube distribution units or "junction boxes" by means of push-fit connectors. This provides a splice-free path between the network hub and equipment the network supports. System Overview ABF is manufactured by Sumitomo Electric Lightwave Corp., Research Triangle Park, N.C. Called the FutureFlex4 Air Blown Fiber System, it uses either compressed air or dry nitrogen to blow small, lightweight, multifiber cables called fiber bundles into previously installed tube cables. Fiber bundles contain from 2 to 18 strands of singlemode 50/125 gm or 62.5/125 .1m multimode optical fiber. These bundles are typically one-fortieth the size of conventional fiber cable of comparable capacity, because no strength members are required to protect the fiber from tensile stress during installation. Tube cable replaces conduit and innerduct used in conventional systems. Flexible and rugged, it contains from 2 to 19 individually marked tube cells, and meets industry specifications for indoor and outdoor applications. Typically, an ABF backbone is constructed with tube cables containing more cells than required at the outset. This provides an in-place right-of-way for growth or changes. Tube cable cells are joined in tube distribution units (TDUs or "junction boxes") by means of simple push-lit connectors. This results in a "through route" between the network hub and the workstation or other sites and functions being suppor ted by the f ibe r infrastructure. The TDU is also the location from which new applications can be supported simply by extending tube bundles from the new location to the TDU and then connecting the required tube cells into the existing backbone. Fiber termination units provide a juncture between the ABF infrastructure and fiber jumpers connected to servers, computers, or other network equipment. Once the infrastructure is in place, fiber installation commences. Bundles are blown into any route of coupled, empty tube cells at rates up to 150 feet per minute, achieving splice-free runs to 6,000 feet, depending on network configuration. Conversely, should requirements change, fiber can be blown out of a tube cell and new fiber blown in. The removed fiber can be used elsewhere since no damaging stresses are imposed on it during either installation or removal. In most circumstances, only two installers are needed to put an ABF system in place. Key Components