Air-Blown Fiber Gives University of Utah Unmatched Flexibility in Campus-Wide Network at Half Cost


In 1990 the underground conduit system supporting the campus-wide network at the University of Utah was in serious trouble. Conduit utilization was out of control. Eight different departments were using up conduit space rapidly; there was no effective plan to control the growing number of cables and the services they carried. No one knew which cables were abandoned, and many conduits were unusable because of improper installation practices.

To bring order to the university's communications infrastructure, a committee was formed in February 1990 by enlisting representatives from each of the eight user departments. Called the Campus Telecommunication Conduit and Cable Excavation Committee, or "Manhole Committee," it quickly determined that the college needed a one-time cable installation that could provide flexibility to support unknown growth of present and future networks.

The committee's first step was to restrict conduit access. Then it addressed a long-term cabling solution to support present and future media, including data, video and telephone networks.

The Fiber Master Plan

Over a two-month period the Committee developed its Fiber Master Plan -- a campus-wide data network topology designed to allow a user logged onto any one data network to establish a link to any other on-campus user or network.

The Fiber Master Plan was designed to employ a campus-wide FDDI ring linking 7 hubs via multi-mode fiber cables. The network was initially designed with plenty of extra fiber to support unknown future growth along the backbone routes -- a campus-wide ring of 96 fiber cables between FDDI hubs and 24 to 48 drop cables to Ethernet and Token Ring network locations within each FDDI hub's local area.

The network installation was divided into 5 phases by specific geographic areas to provide service to 63 buildings (see Figure 1). At initial planning, 11 additional buildings were noted as possible future additions to the network. They, and 10 others, have since been connected.

By August 1990, The Fiber Master Plan evolved to a data network Request For Proposal (RFP) that was released to more than 30 optical fiber cable and equipment suppliers. While the RFP addressed current network requirements, future needs were unknown. Respondents were asked to propose types and quantities of fiber that, in their estimation, could accommodate future requirements.

Approximately two thirds of the suppliers responded. All except one proposed conventional fiber optic cabling. Sumitomo Electric Lightwave Corp. (SEL) recommended a technique described as "air blown fiber." Called FutureFlex¨, the solution, according to SEL, would address the requirements of the university in 1990 while providing the capability to support ongoing communications growth in an economic manner.

The SEL proposal was accepted by the university because it addressed three critical design aspects: long-term flexibility, long-term cost and long-term expandability. The technique enabled the university to install less fiber than initially planned for in its effort to accommodate future growth. It also reduced end-to-end attenuation due to the elimination of field splices while its more direct fiber routing capability minimized design issues in several of the longer fiber spans.

Air Blown Fiber

Air blown fiber utilizes tube cables -- jacketed bundles containing 1 to 19 individual coded tube cells -- to provide routes through which optical fiber bundles are blown using compressed air (Figure 2). Within building envelopes, tube cable normally replaces costly innerduct. In outdoor environments, tube cable is direct buried or pulled through conduit like innerduct. During the installation process, no fiber is in the cable.

Individual tube cells within tube bundles are interconnected at tube distribution units (junction boxes), providing a splice-free point-to-point fiber path. Once any given route is established, fiber bundles containing up to 18 single mode, or 50 mm or 62.5 mm multi-mode fibers are installed by "blowing" them through cells using compressed air. The bundles are installed at rates up to 150 feet per minute. Standard blowing distances are 3300 ft. for 2- to 6-fiber bundles and 1650 ft. for 12- to 18-fiber bundles. These distances can be doubled by running two sets of blowing equipment in tandem.

To allow for future growth, the contractor installed tube bundles with more cells than required to meet current needs at the university.

At the University of Utah, the major long-term benefit of using air blown fiber is that it permits quick installation of the exact fiber types, counts, and routes needed. It also provides the means to easily add fiber on demand without disturbing existing networks. An immediate benefit is that it was put in place at less than half the cost of conventional optical fiber systems. Top contributors to savings are reduced fiber counts and eliminating field splicing labor.

The Installation

On May 21, 1991, the cable installation contract was awarded. The entire project design utilized 190,000 feet of 6-tube LAP (laminated aluminum polyethylene) cable and 330,000 feet of 6-fiber 62.5 mm fiber bundle.

Phase I of the installation began in June 1991 and finished on schedule in October. In fact, the installation was well ahead of schedule until the presence of crushed conduits and abandoned cables made it impossible to install tube cables. In some cases, the installation crew was able to successfully install the tube cables alongside existing cables. Otherwise change orders were issued. As expected, conduit problems continued to arise throughout the project.

Although a total of 54 change orders were issued, many were occasioned by the flexibility of the air blown fiber system. This allowed the university to accommodate last-minute changes to the fiber routes by simply changing tube interconnections at distribution units.

The final phase -- Phase V -- of the installation included the campus' Research Park, a location unserved by conduit. The contract included new manhole and conduit system construction, which was completed the fall of 1992. This phase also had the longest fiber bundle installation in the entire project -- two 5,900 feet links between the Phase IV and V FDDI hubs.

Looking Ahead

Upon completion of the initial project, the university began addressing new network requirements. Adding fiber into existing tubes is a matter of simply interconnecting empty tube cells and blowing needed fiber bundles into the new tube routes. Only two trained installers are needed to blow in new links.

Since initial project completion, a major growth area was the University Medical Center, a 4-building complex located adjacent to Phase IV. Air blown fiber was installed throughout the University Medical Center to satisfy internal interconnectivity requirements. Also, services in the new Moran Eye Center were connected to the Hospital network via an air blown fiber riser backbone and two 3,400-ft. air blown fiber spans. In the Health Sciences building, the technology was employed to provide fiber to the desk. The University Hospital continues to expand the its air blown fiber network as new applications arise and changes occur.

Additionally, the university has utilized its new system to provide a single-mode fiber link to TCI, the local cable TV company, to broadcast on-campus Public Television and Interactive Learning Channels. This is an example of a single-mode requirement that was unknown and not specifically addressed in the original Fiber Master Plan.

The university's network underg'es major changes day by day. For example, due to new building construction, many fiber links to the Phase I hub were removed (blown out) and rerouted (blown in) through new tube bundles to a new Phase IV hub, which has been relocated to the Language and Communications Building. New conduit was also installed to link the Hospital complex to the Phase II hub.

As another example, the university is planning to install air blown fiber to link buildings throughout nearby Fort Douglas to the existing campus network. Fort Douglas, partially abandoned by the Army and turned over to the University of Utah, will be utilized in part for research.

A Tube Distribution Unit -- Individual tube cells with tube bundles (that contain up to 19 tube cells) are interconnected at tube distribution units, providing a splice-free, point-to-point fiber path. Unconnected tube cells are available for expansion purposes.

Cable Management

With all of the changes the university has undergone since 1991 and continues to experience, managing the complex network of conduits, tubes and fiber bundle routes has become a tremendous task. There are no cable management program packages currently available that can handle the university's complex fiber network and provide the level of user friendliness required.

To address this challenge, the University's Telecommunications Department, in cooperation with the Geology Department, developed a Geographical Information System (GIS) utilizing a detailed map of the entire University, including all communications hardware types and locations along with conduit, tube cable, and fiber bundle routes between and within all buildings on campus. This tremendous amount of data has been entered into the GIS database along with precise geographic information provided by detailed aerial photography. It delivers extremely detailed network information for any location along any communications route on campus at the click of a mouse.


Over the past five years, air blown fiber has proved itself a viable technology for addressing expansions, changes and modifications to the campus-wide network at the University of Utah. The ease with which optical fiber can be added, rerouted or removed from tube cells solves, in an economic manner, one of the most difficult challenges faced by network administrators: how to plan for the future.

This article originally appeared in the 06/01/1996 issue of THE Journal.