Air-blown fiber links past, present, future

Communications News,  Oct, 2001  

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National Park Service's environmental and process-control network achieves maximum flexibility with fiber-optic cabling.

Independence National Historical Park in Philadelphia, home of Independence Hall and the Liberty Bell, is a renowned American landmark. Each year, millions of Americans and tourists from around the world visit Independence Park to learn about the events that led to the founding of the U.S.

As part of a multiyear phased renovation and expansion, the U.S. National Park Service (NPS) designed and engineered a centralized chilled water plant and process-control network within the park. The campus-wide data communications network will provide centralized control of the heating, ventilating and air-conditioning (HVAC) system, so critical to the environmental maintenance of the park's historic buildings and documents. The LAN also controls the fire-protection system for Independence Hall and other historic sites.

NPS specified Sumitomo Electric Lightwave Corp.'s FutureFLEX air-blown fiber-optic (ABF) cabling system for the network's data communications backbone. According to Jack Dunleavy, on-site project manager for NPS, ABF technology was specified chiefly because of its flexibility and versatility. "We were able to install the data highway once, and it can be reconfigured over the years as the needs of the park change and grow," he explains.

The tube cable infrastructure was routed from the plant at the east side of the park to Independence Hall on the west side. Tube distribution units were installed underground in manholes outside of each historical building along the route, storing sufficient tube cable to provide for future network expansion. As additional buildings are added to the network, stored tube cable need only be extended from the local connection point into the building, with fiber blown back to the central control point.

Next, California-based Canus Corp. installed FutureFLEX 19-cell tube cable, which would provide ample capacity to meet any future network demands. Canus Corp.'s project coordinator Reed Wiegle notes that there is more than enough spare tube cable and cell capacity to link into the new facilities now being planned for north of Independence Hall.

HISTORY MEETS TECHNOLOGY

The ABF system infrastructure consists of flexible tube cables used in place of innerduct. Tube cables may contain up to 19 coded tube cells, which can be joined in tube distribution units (TDUs) or junction boxes using simple push-fit connectors. TDUs replace conventional fiber splice hardware at tube cable transitions and branching locations to provide point-to-point connectivity between the computer room or network hub and the application. Fibers typically come in bundles, ranging from two to 18 fibers each, to deliver a maximum capacity of 342 fibers in a 19-cell tube cable.

Once the tube cable infrastructure is in place, lightweight bundles of single-mode or multimode fiber are blown at speeds up to 150 feet per minute through a predefined route on a stream of nitrogen, using specially designed equipment. Installation is fast and easy, requiring no more than two trained technicians. Cable runs may exceed 6,000 feet, and the fiber path may traverse outdoor, riser and plenum tubes in a single run. Since the fibers are not pulled, installation damage ceases to be an issue. Moreover, point-to-point connectivity eliminates splices--the most common site of network failure.

In almost all ABF installations, tube cable is installed with more cells than are currently required to ensure room for expansion. Unused cells are capped off within TDUs until needed. Network expansion or reconfiguration can be accomplished quickly by extending tube cables from the nearest TDU. Fiber bundles can be upgraded or replaced by blowing cable through unused cells, or by blowing out old fiber (which can be reused) and blowing in new--all without disrupting the existing network.

FUTURE PROOFING INSTALLATIONS IN 18TH-CENTURY BUILDINGS

Since the original installation, the Independence National Historical Park network has undergone a series of expansions. When the NPS opened a new display in the West Wing of Independence Hall--which holds one of 25 known copies of the first printing of the Declaration of Independence, a copy of the Articles of Confederation, and a final draft of the U.S. Constitution--Canus connected the existing tube cables to the new West Wing display. This installation required more than 2,200 feet of six-strand multimode, fiber-optic cabling. Several more historic buildings have been linked into the LAN server with point-to-point ABF cabling.

Wiegle admits that the installation has not been without its challenges--most of them due to the age and space constraints of the historic structures. "Installing the tube cable across the 18th-century basement of Independence Hall to link into the original system involved some pretty tight spaces," he recalls. "Also, extending the tube cable from tube distribution units means working in manholes. Fortunately, the compact size of the tube cable works to our advantage in space-constrained situations."