Fiber network hauls stable telephony
New Haven, CT-based Southern New England Telephone Co., or SNET, is increasing the reliability of voice services for its Stamford, CT, customers by using a hybrid fiber/coaxial-cable network infra- structure. This commercial delivery of telephony service provides power to fiber nodes in a hybrid fiber/coaxial-cable plant from the company`s central office.
Telephony is being carried over a hybrid fiber/coaxial-cable network using commercially available equipment from multiple suppliers. For the first time, a major U.S. public network has moved residential customers to the new platform.
During the next 15 years, SNET plans to replace its existing twisted-pair copper-cable network with a broadband full-service network that provides telephony service and other competitively priced products.
This network system places its power supplies--batteries and generators--in the company`s central office, which provides backup power in case of commercial electrical power outages. The system does not depend on the local electric power grid or on structures containing lead-acid batteries or noisy generators located in the neighborhoods. It comprises a SNET-designed cable that features a central conduit for the optical fiber and an array of aluminum power conductors packed on the outside of the conduit, encased in steel armor and then covered by a polyethylene sheath. Manufactured to SNET`s specifications by Okonite Co. in Paterson, NJ, the cable reportedly does not have the maintenance, environmental and site hassles associated with remote, battery-powered sites, according to SNET network planners.
This fiber-optic cable carries up to 480 volts alternating current from the SNET central office to local nodes, where fiber-optic lines connect to coaxial cables. These coaxial cables carry the same low-power current--approximately 60V when the telephone is ringing--as today`s telephone lines (see Lightwave, December 1995, page 3).
Typically, at least six optical fibers--four for telephony, one for video and one spare--extend from the central office to neighborhood optical network units. From there, each of four coaxial cables stretches past almost 50 residences. Depending on housing density, each cable can stretch several kilofeet.
Charlotte Denenberg, SNET`s chief technology officer, emphasizes that the company is concerned about retaining the high level of telephony reliability as it makes the transition from traditional copper wire to optical fiber and coaxial cable.
"Up until now, fiber-based information networks have not been able to deliver this level of reliability because they depend on the commercial power grid backed up by local powering in the form of refrigerator-size generators and lead-acid batteries in nearly every neighborhood," Denenberg says.
If these claims prove to be true, this SNET approach to power the hybrid fiber/coaxial-cable network could increase confidence for fiber in the loop throughout the telephone industry.
In assessing SNET`s plans, Vern Mackall, a senior analyst at Northern Business Information, based in New York City, says he is impressed by SNET`s concerns about "life-line" telephony service. "Telephone customers always want their telephones to work--no matter what happens," he says.
"SNET`s Connecticut service area is attracting new competitors because of its high population density, high per-capita income and favorable regulatory environment. Cable-TV companies are targeting the state for rollout of residential telephone service. By providing its own network powering, SNET is in a position to differentiate its service reliability from that of cable companies, whose networks rely on power from the utility companies," Mackall says.
Ronald O. Brown, an industry consultant in Melrose, MA, thinks SNET is making an excellent move. "However, I raise the issue about how SNET plans to market and price this service as a competitive service or as a traditional protected monopoly carrier," Brown says. "If [they offer it] competitively, it will be a financial success, while protecting SNET`s market base."
Brown also notes that the telephony industry is currently in a "marketing free-for-all," and market dominance of the wire-line side is still "up in the air."
To compete in this market, SNET is developing its patent-pending hybrid fiber/coaxial-cable network architecture using AT&T Network Systems HFC-2000 broadband access system. Scott Grout, program management director at AT&T Network Systems in Morristown, NJ, notes that the broadband access system serves as the host digital terminal in the SNET central office. "SNET is providing analog-video, two-way data services and telephony," he says. He notes three components of the HFC-2000 system:
The host digital terminal is the hub site for the system, integrating broadband and narrowband services--voice, video, graphics and data. It has a TR-303 digital switch interface.
Fiber power-conversion nodes allow the service provider to bring fiber into a neighborhood serving an average of 200 homes. Fiber nodes receive downstream optical signals and convert them to electrical signals for transmission to network interface units.
Network interface units installed near or at a customer`s home split out the downstream telephony and video signals and transmit them to the home using existing premises wiring.
Bill Seekamp, SNET spokesman, says that initially, the company anticipates having 50 customers for its telephony system. The company plans to have 80,000 customers on its network by the end of 1996 and 500,000 customers within the next three years.
Hoshang Mulla, director of network planning at SNET, discusses how SNET engineers are bringing telephony reliability to this network architecture. "Customers can use their telephones when storms cause local power outages because central offices generate back-up electricity to power our network. We took that power supply model into the new network by placing power conductors around our fiber-optic lines. Being glass, the lines cannot conduct electricity," Mulla says.
He notes that this system, with its steel-armor sheath and extra insulation, provides significant protection against possible cable breaks. Mulla points out that by locating the power source at SNET`s central office, SNET continues to provide customers with highly reliable service that is independent of commercial power outages. q