In-sewer broadband deployment: beauty in simplicity

Oct. 1, 2001
SPECIAL REPORTS: Installing Networks

Pulling fiber cable through sewers may not be the sexiest new technology, but it's proving to be effective and efficient.

STEPHEN MERRILL, CityNet Telecommunications Inc.

In the telecommunications industry, as in life, sometimes the best ideas are the simplest ones. That is the notion driving the latest technology for delivering fiber-optic networks into end-user buildings-the deployment of optical cable through city sewers.

Today, fiber-optic networks that deliver broadband services run between continents and countries, between cities, and as large beltway rings encircling cities. What's missing is the vital link between the individual building and those larger metro beltway fiber-optic rings.

This gap, still reliant on technology from the era of Alexander Graham Bell, is filled with older and slower copper phone lines. The last-mile is the missing link to a true end-to-end, all-optical broadband network communication path. And for the businesses and people in the buildings, the aging last mile of copper wire is responsible for huge bottlenecks and major slowdowns in data, voice, and video traffic.

A great many companies are involved now in trying to close the gap, but nearly all methods for laying underground fiber-optic cable involve digging trenches in streets. This trenching damages valuable urban infrastructure, causes traffic nightmares for city commuters, and is a headache for elected officials. Recently, however, the simple idea of using sewers has spawned a whole new way of bridging the last-mile divide.

Rather than digging up streets, why not use pathways already built underground? This simple question was the beginning of a novel new approach by companies like CityNet Telecommunications Inc. (Silver Spring, MD) and a handful of other companies, such as CableRunner North America LLC (Miami) and Stream Intelligent Networks Corp. (Toronto). Using robots to do the "dirty work," fiber cable is being pulled through city sewer systems to install broadband networks.

CityNet pioneered the new technology in the U.S. by developing in-sewer robotics, and the company's small pipes robotics is unique. Cable Runner uses technology deployed in man-accessible sewers, while Steam uses a drill and dowel technology.
Two technicians lower the sewer access module (SAM) into a manhole to begin fitting conduit for the fiber-optic cable that will run through sewer lines to provide high-speed broadband access.

For about two decades, robotic technology has been used to clean and inspect sewers and make spot repairs. A thorough survey of state-of-the-art sewer technology revealed that the company producing the most reliable, sophisticated, and adaptable robots in the world was Ka-Te Inc. This group of Swiss engineers had been working for about five years on ways of adapting their sewer robots for new uses.

Ka-Te's technology supported an evolving methodology and system of constructing a carrier's carrier outside plant fiber-optic network. The technology proved flexible and reliable, so CityNet entered into an agreement with Ka-Te to purchase robotics systems for fiber network deployment within sewers.

Ka-Te's patented robots and the method for installing in-sewer fiber-optic cable brings a unique and exciting new era to last-mile fiber deployment. Although more companies are bound to enter this intriguing market, few companies can currently do in-sewer installation in 8-inch-through-28-inch-diameter sewer lines without drilling.

The installation of fiber-optic cable in a sewer pipe is the merging of leading-edge technology with a technology that has been around for centuries. It requires equally an understanding of sewer systems and hydrology as well as telecommunications and telecom engineering. It means creating the least intrusive system possible, while assuring a solid and resilient conduit for the placement of fiber-optic cable. The system has to meld with the sewer environment to avoid any interference with the sewer's primary mission: to support the distribution and removal of waste. Anything that might eventually cause the degradadation of the sewer function is rejected.

The process of installing in-sewer fiber-optic cable begins with the managers of municipal sewer systems-city governments. Public officials hold valuable information on the health of sewer systems, the size of the physical infrastructure, the size of pipes, the history of cleaning and maintenance, and the history of trouble or events. This information expedites assessment and planning, targets areas that need to be engineered around, and provides background for the physical inspection of the sewer.

First, the buildings to be wired are targeted. An initial assessment is made of which pipes might provide the best routes. Following the assessment, the arduous process of gathering critical information begins.

Gathering and validating the data by inspecting the sewer systems takes about three months and varies with the reliability of the records and whether the records are kept in paper or geographic information system (GIS) format. Closed-circuit television robots help assess the condition of the pipes, often producing surprises. The costly proprietary robots used by CityNet-robots known as sewer access modules, or SAMs-are used for first-level inspections if the records are reliable and evaluations have been recently performed. Working in sewers underground is a constant process of risk evaluation.

To gather the most reliable data and allow the clearest possible image as videotaping begins, the pipes that will carry the robots must be jet-washed. The camera-equipped robots assess stress-cracking, opportunities for corrosion, and other interior conditions of the pipes. Pipes that will be used for conduit sometimes require repair. The installer-in conjunction with the municipality and/or sewer operator-performs all kinds of sewer-line rehabilitation, including point repair, relining, and pipe bursting for sewer-line enlargement.

Meanwhile, using a "mapping head," the SAM sends digital video of the line while simultaneously mapping the sewer systems that will be wired. The SAM is also equipped with two measuring wheels to provide reliable linear distance measurements between laterals as well as mark the distance between impediments. It is necessary to know precisely where each lateral comes into the sewer line so the conduit can be engineered to avoid the laterals.

While photos of the sewer's interior are captured on tape, computers are capturing data sent back by the robot to a crew manning the robot command center. The command center simultaneously records information for the physical field placement of equipment, information on the pipe inspection, and measurements. The goal is to engineer infrastructure with a lifespan in excess of 25 years.

Command centers are outfitted in medium-duty trucks that consist of computers, monitors, auxiliary replacement parts, a small winch that lowers the SAM into manholes, and the hose that is the robot's "lifeline"-an umbilical cord containing all video and communications wiring (see Photo on page XX). Command centers also include a generator, a van, and the conduit placement trailer. The compact configuration of the equipment and the small crews-a team leader and two technicians-allow for the discreet after-dark deployment of several teams simultaneously. This deployment strategy prevents the work from interfering with the traffic flow in metropolitan downtown areas during the day and allows work to proceed when sewers are least likely to be functioning at peak capacity.

When the sewer system has been mapped, repaired, and prepared, the robot mapping head is changed to a clamp placement head. The size of the head depends on the size of the pipe and ranges from 8 inches to 28 inches in diameter. Stainless steel alloy ring clamps are placed inside the sewer pipe about every 5 ft and are held to the inside of the pipe by tension. The steel alloy won't rust in the watery environment and is the best material to withstand the rigors of the sewer. The ring clamps are made by Ka-Te, while the conduit and fiber-optic cable are manufactured and supplied by companies like Alcatel USA.

Crews work from manhole to manhole, usually a distance of 250 to 300 ft, remotely maneuvering the SAM to monitor the process by video. Everything must be seated perfectly before the first conduit can be put into the ground.

Connectors on the ring clamps are installed to hold between three and nine runs of conduit. When all clamps are in place, the SAM resurfaces. A conduit-setting device is attached to the robot, and the process of installing conduit begins. Each conduit is placed in its own retainer clip. The installation of the conduit is laser-guided to assure the perfect connection between conduit and connector.

Throughout the process, all installation information is stored and saved to provide a complete plant record for the future (e.g., when a new building is built or an old one torn down). The fiber-optic cable infrastructure becomes part of the city planning process. Digital and GIS-based plant records must be absolutely correct for future generations of city leaders.

At least three conduits are installed in the sewers, the maximum number that can be placed in an 8-inch sewer pipe without degrading the pipe's primary mission. Conduit is never allowed to occupy more than about 3% of the pipe's total volume to maintain efficient hydrology.

After the sewer system has been mapped and the clamps/conduits placed, fiber-optic cables are installed in the conduits. The fiber cable conforms to telecommunications industry standards with a specially designed outer jacket for the sewer environment.

To assure the long lifespan of the network, an aggressive ongoing cleaning routine and regular inspections are set up following installation. The entire network is designed to stand up to the rigors of routine maintenance, such as water pressure of 2,500 psi-the force of a standard sewer jet wash.

This innovative methodology for placement of fiber-optic cable is least invasive and non-intrusive. If the process seems simple, it is-and that's its beauty. It is simplicity-in tandem with some very sophisticated equipment and meticulous attention to detail.

Stephen Merrill is senior vice president of engineering for CityNet Telecommunications Inc. (Silver Spring, MD). He can be reached via the company's Website,

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