While most of the talk about expanding broadband access for the American public has focused on rural customers, much of the activity is in metropolitan areas. Metro networks are expanding rapidly because they encompass many types of networks, not just broadband Internet.
Cities and suburbs are installing communications systems to connect administrative, public safety and other city offices. They are installing surveillance cameras for security and traffic monitoring. They are monitoring and controlling traffic signals to improve traffic flow and save energy. Schools provide high-speed Internet to students and school administrators. Municipalities are installing wireless systems for both private and public use. Utilities are expanding their communications systems to increase efficiency and read meters remotely. Many cities also are realizing that they can lease “dark fibers” to phone or cable TV (CATV) companies as well as other organizations that desire high-speed connectivity.
All of these applications are based on optical fiber, virtually all single-mode. Most fiber optic cables are installed underground, although some areas still use aerial cables. Understanding how to install the cables with minimal disruption of the day-to-day city operation is the secret to a successful installation and sometimes a successful bid on a project.
Metro network issues
A decade ago, when companies were installing fiber practically everywhere to expand or offer competitive phone, CATV and Internet services, it was not uncommon to find city streets being dug up time after time as each new company negotiated rights-of-way individually with the local governments. Each time a company dug up the streets, snarling traffic, the pavement quality declined because repairs generally were not of sufficient quality or durability.
Smart municipal administrations quickly learned to require whoever was digging up the street to install extra conduit. Ownership of the conduit transferred to the city and was partial payment for the access to install cables. The practice allowed the city to sell access to other companies (or to install their own municipal fiber optic networks) without digging up the streets again. Now cities are working with companies and contractors to develop new techniques for installation that are less disruptive.
When cities realize they can lease fiber networks to companies that wish to offer phone, CATV and Internet services, the installation of municipal fiber networks just makes sense. Local governments have also discovered several funding sources that offset the cost of installing their own networks. Federal funds are available for education (connect the schools), homeland security (connect the public service departments and install surveillance cameras) and transportation (install a smart traffic light system). And, of course, more than $7 billion in stimulus funds have been made available for installing broadband for underserved areas, many of which are the inner cities.
Some municipalities, such as Santa Monica, Calif., have made use of all these funding sources and have installed many additional fibers for other purposes. Santa Monica City Net leases fiber for CATV and fiber to the home (FTTH) and offers connections to many companies based in the city that want private high-speed communications access. Many cities have discovered systems—such as Santa Monica City Net—can pay for themselves with sales opportunities.
A local electrical utility is building another well-known successful metropolitan network in Chattanooga, Tenn. Chattanooga gained fame as the first city to build a 1-gigabit-per-second (Gbps) FTTH network, beating Google, which will build a network in Kansas City, Kan., and Kansas City, Mo. The utility that is building the network will also use it for reading meters.
Google, of course, deserves a lot of credit for the interest in metro networks. The company’s promise to build the first 1 Gbps metro FTTH network received more than 1,100 applications from American cities interested in providing higher speed broadband connections to their citizens and maybe bypassing other communications providers who were less than enthusiastic about upgrading systems. Google has even worked hard to encourage new technology and installation techniques that can enhance network performance, reduce energy consumption and simplify installation.
Verizon is another major corporate contributor to the development of new metro network processes. In the company’s massive installation program to bring fiber to the home with its FiOS system, Verizon examined many of the installation processes and components used to reduce the time and cost of installation. In addition, the company needed technicians who could install the fiber outdoors and in multiple dwelling units and then hook up and troubleshoot the phone, video and Internet services.
Fiber optic components and systems
While the premises cabling market still uses a lot of multimode fiber for CCTV and computer networks, outside plant and metro networks are almost entirely based on single-mode fiber. Once you get outside a building, the distances are usually too long for multimode fiber, so equipment designed for metro systems will be compatible with single-mode fiber.
Unlike telco systems, which have multiple single-mode fiber types to choose from, depending on the length and bit rate of the links, metro systems generally use regular single-mode fiber (G.652 is the international designation). However, low water peak fiber may be chosen for its ability to upgrade to wavelength-division multiplexing (WDM) for future expansion, saving the need for installing additional fibers. And while telcos install cables with many extra fibers, metro systems may choose to limit the number of fibers for smaller diameter cables, which simplifies installation in crowded ducts.
Cabling for metro networks today is generally installed underground, although some cities continue using aerial installation; it’s a cheaper solution than paying the cost to bury all their aerial cables. When used, aerial cables will often be lashed to current messenger cables or other copper communications cables. Self-supporting fiber optic cables are an option where poles are already overloaded with cables.
Some specialized underground cables and ducts have been developed for metro applications, often to reduce cable size and allow easier installation in crowded ducts. Sometimes, even air-blown fiber is used. Air-blown fiber uses small plastic tubes that are installed like cable. Then special fibers are blown into the tubes. Advocates of air-blown fiber like to point out that it allows upgrades by forcing out old fibers and blowing in new ones, justifying the higher initial costs.
Like other outside plant installations, splicing is generally performed with fusion splicers, and the splice closures are carefully stored in manholes or pedestals. And since it’s single-mode fiber, termination is performed by fusion-splicing pigtails onto the fibers. Prepolished splice connectors, including new designs that use fusion splicing instead of mechanical splicing, can be used if breakout kits are installed on the cables.
One of the secrets to success for a contractor interested in metropolitan networks is learning how to install fiber with minimal disruption to the city. New techniques for fiber installation, many developed for FTTH, are proving to be highly useful in metro installs.
Obviously, the best situation is having conduit space available already. Many cities have conduit with fiber ducts installed, so pulling fiber is simple. Sometimes conduit space can be expanded using some new styles of ducting, including collapsible types that take up practically no space but protect the fiber optic cable and reduce pulling tension. Installation is simply a matter of pulling cable from manhole to manhole, splicing as necessary, and storing service loops.
Where conduit is not available—either for the full cable run or drops into buildings, pedestals, or to poles for wireless access points, CCTV cameras, and traffic signal controls—microtrenching techniques can be used. The latest version of microtrenching equipment cuts a narrow (less than 1 inch) groove in the pavement, typically less than 12 inches deep, vacuuming up the debris as it goes along. Cable or small ducts for pulling cable or even air-blown fiber is installed in the groove. After the duct or cable is installed, the groove is backfilled with grout that meets the same standards as the pavement.
The shallow depth of the microtrenching groove means minimal interference with other underground utilities. Installers and equipment providers claim that more than five miles of cable can be installed per day at up to 75 percent cost savings and with reduced traffic disruption. The expensive microtrenching equipment is already available for rental, making the investment in such equipment unnecessary.
Equipment rental is one of the techniques that Google identified as a way to save costs in metro installations. The company was so interested in the technique that it held a microtrenching race in the parking lot at the Google campus between equipment vendors to encourage competition in developing better equipment.
Additional cost savings may be possible using another technique developed for FTTH: prefabricated cable systems. Since single-mode termination is usually performed by splicing pigtails onto a cable and sealing splices in a closure for protection, termination can be time-consuming and expensive. FTTH systems often use prefabricated cables with weather-resistant terminations on one or both ends. Pulling terminated cable into ducts is usually not possible, but if one end is finished, the unfinished end can be pulled through the duct so that only one end requires splicing.
Companies such as Google and Verizon have done a good job of promoting these new technologies and their advantages. Some municipalities have well-informed personnel who keep track of new technologies such as microtrenching and prefab cabling systems and want to include them in their metropolitan network projects. Contractors familiar with these techniques have a competitive advantage and should, of course, inform municipal engineers planning projects of the advantages and particularly the potential cost savings of these techniques.
HAYES is a VDV writer and educator and the president of The Fiber Optic Association. Find him at www.JimHayes.com.