Rural fiber network steers information superhighway to small communities

George Kotelly

Aptly known as "fiber to the farm," a fiber-optic-based distribution network targets the telecommunications requirements of dispersed, low-subscriber-density towns. To bring the voice, video and data service benefits of the information superhighway to farmland America, E/O Networks in Hayward, CA, has started a field trial of its FDS-1 fiber distribution system. Working with network consultants Martin and Associates and with Brookings Telephone, both located in South Dakota, the company has deployed its first engineered equipment/ system. The network is initially delivering basic telephone service to 40 subscribers.

According to Alan Negrin, president and chief executive at E/O Networks, "The rural market is served by 1200 small, independent telephone companies in the United States and Canada. These companies want to replace their aging copper plant with fiber-based systems, but until now, they haven`t had a viable solution."

Most fiber-based networks are targeted to the urban market where short loops and high-subscriber densities justify expensive systems. The FDS-1 suits the rural market, where subscribers are often miles from their neighbors or the central office.

The rural network employs a fiber-to-the-node architecture using six-strand fiber-optic cable in a ring-survivable configuration. The fiber distribution loop covers distances to 75 miles from the central office, or 150 miles total. It supports 384 digital signal, level 0, subscribers on two fibers for telephony transmission.

On two other fibers, the network can deliver 110 channels of amplitude-modulated video and more than 500 channels of digital video. The remaining two fibers can support high-speed data services to 1.544 megabits per second, including Ethernet and integrated services digital networks.

Approximately 30 optical network units can be connected to the ring network. Containing environmentally protected electronics, the ground- or pole-mounted units pass along the full-bandwidth transmissions, and deliver telephony services via copper wire drops and video signaling via coaxial cable to subscriber premises.

Notes Leif Hoglund, vice president for marketing at E/O Networks, "Each optical network unit can handle 4 to 96 subscribers and has the capability to interface to a telephony terminal, a video optical receiver and transmitter, and a future broadband terminal."

According to the Rural Electrification Agency, a federal government agency that provides communications and electricity to rural areas, international low-density telecommunications market sales reached $364 million in 1994, and are projected to more than double--to $783 million in 1997. Low density is classified as fewer than 100 subscribers per mile. The agency claims there are 8.5 million lines in the United States and 3 million lines in Canada that can be graded as rural. It contends the North American market segment totaled $287 million for 1994.

Market comparison

In urban markets, the distance from the central office to the subscriber is usually less than three miles, business customers dominate revenues and the competition includes competitive access and cable-TV providers.

To support urban customers, the regional Bell operating company networks have to connect with existing operations support systems, employ complicated software and mandate extensive system training. These factors are not cost effective for rural networks, which prefer personal-computer-based systems, user-friendly interfaces and little built-in overhead.

In rural markets, the central-office-to-subscriber distance is much longer than three miles, residential customers dominate revenues and competition is virtually non-existent. Rural subscribers typically receive telephone services by wire and television services via satellite or TV-station broadcast.

Costs rule

Because of the long connection distance from the central office to rural subscribers, the costs of purchasing and installing fiber-optic cables are pre-eminent. To lower these expenses, the rural network employs a six-strand fiber cable instead of the more expensive 12- to 48-strand fiber cables used in many urban networks

According to E/O Networks, a 10-mile, six-strand fiber cable for the rural network can be purchased for approximately $29,000. On the other hand, a 10-mile, 48-strand fiber cable for an urban network costs nearly three times more, or approximately $82,000. Labor and installation expenses boost the total network cost.

In urban networks, the generally deployed fiber-star and passive optical network architectures possess limited range in terms of full-bandwidth transmission to optical network units. This bandwidth is typically limited to cable-connection distances of fewer than three miles without signal boosting and retransmission. These architectures also implement expensive remote terminals to retransmit, boost or split the signals going to optical units farther out in the network. Also, if more bandwidth is needed, urban networks would incur additional fiber cable installation costs.

In contrast, the rural network supports communications services to optical units located 75 miles from the central office and accommodates future bandwidth services by reserving two installed fiber pairs for prospective video and data services. Furthermore, the central office in a rural network can transmit its full bandwidth capacity to 30 optical units without incorporating costly intermediate devices.

In rural networks, approximately 60% of service outages are caused by accidental cable cuts. Because of longer loop distances, repair and restoration services for rural networks can be time-consuming, complex and expensive tasks. Urban-type star and passive networks provide little protection against this failure mode.

The rural network, however, implements a counter-rotating ring fiber architecture that recovers almost instantly--in about one millisecond--to a cable or device failure, undetectable by most users. Also, despite a cable cut to any optical unit on the rural network, all the other optical units remain ring-connected to the disconnected optical unit and continue to receive and transmit signals to that unit.

Adds Hoglund, "With our folded-ring configuration, all the bandwidth is available to all the optical network units. These units can be connected anywhere on the ring network without taking any user off service."

With ring architecture, full-bandwidth delivery and the elimination of intermediate network devices, rural networks promote flexible and straightforward planning, installation and operation.

Upgrading the rural network does not affect telephony services. Two of the six fibers in the cable are reserved for future broadband services and two others are reserved for data services. All optical network units readily accommodate a broadband-terminal connection. Consequently, the rural network can be upgraded to future video services without incurring substantial infrastructure costs. Twisted-pair copper wires connected to the optical network units are used for all standard telephony services.

The optical network units, which are used as remote terminal digital-loop carriers, support 12,000-foot copper-wire drop links and 1500-foot coaxial-cable links to customers. Furthermore, each optical network unit on the ring handles a different number of connected users: One might support 500 users and another might support only one or two. q