Fiber-optic architecture evolution evident at cable-TV exhibition

Aug 1st, 1995

Fiber-optic architecture evolution evident at cable-TV exhibition

GEORGE LAWTON

Many cable-TV operators who attended the Cable-Tec Expo held in June in Las Vegas seem to be evolving their cable networks to a hybrid fiber/coaxial-cable architecture. According to these operators, this evolution to hybrid networks should increase business opportunities, but at the same time, it opens the door for service-reliability problems.

The conference focused on reliability because many cable-TV operators are looking at adding new services such as telephony. Through these services, cable-TV operators will need to improve their customers` perception of reliability and service to compete successfully with telephone companies.

Ron Hranac, vice president for engineering at Coaxial International in Denver notes, "If we cannot get good reliability and quality, then it will be tough to get into the telecommunications environment."

Hranac cites a study, Outage Reduction, from Cablelabs, Louisville, CO, which reports that two outages every three months is an acceptable level of outages for the cable industry. The report also states that after a 10-minute outage, customers are as outraged as they are after an outage that lasts an entire day. And, the greater the number of outages, the more likely customers will cancel or downgrade their service.

Chris Barnhouse, vice president for technology at Time Warner Cable, discusses the company`s progress in deploying telephone systems. He says it would have been easy to go in as the low-cost provider of a low-grade service, but that would have locked the company out of a number of lucrative service opportunities. He says, "We made a decision to go head-to-head with the local exchange carrier. There are some stringent qualifications that go along with it."

Al Johnson, president at Synchronous Communications in San Jose, CA, presented the concept of a layered network architecture, which he believes will lower the capital cost of adding new services. One way that cable operators can decrease their transmitter costs is to use a high-power transmitter with an optical amplifier.

This allows the signal from one laser to be split onto several different fibers. But that also means that several neighborhoods will receive the same information. The drawback to this approach is that for telephony and other interactive services, most cable operators are looking at multiplexing voice and video information onto the same fiber. Consequently, they want a single laser feeding the smallest possible number of homes so that they can maximize the bandwidth each home has for interactive services.

Johnson`s layered network architecture uses a single 1550-nanometer transmitter connected to an optical amplifier to send out the major broadcast channels to every neighborhood. After this signal is split onto several fibers, each split signal is multiplexed with a low-power 1310-nm laser before being sent to the neighborhood. At the receiver, another wavelength-division multiplexer splits the signals so that multiple photodiode detectors can receive them.

Cable-Tec Expo`s exhibition area featured new fiber-optic products and technologies for the optical-fiber and cable-TV industries. For example, Minneapolis-based ADC Telecommunications Inc. has boosted the capacity of its fiber frame so that 1440 terminations can be accommodated in a single 7-foot-high rack. That rack outperforms typical fiber frames, which only support 200 to 800 terminations in the same-sized case. It features a removable module that can hold four fiber terminations and that can be easily moved when expansion is necessary.

ADC Telecommunications has also teamed with Bell Communications Research to develop an element manager for ADC`s Homeworx hybrid fiber/coaxial-cable platform. Although ADC Telecommunications has been developing its own proprietary network management system, this agreement with Bellcore will ensure that its network management system interoperates with a variety of equipment.

Wavetek Corp., in Indianapolis, demonstrated its Flash mini-optical time-domain reflectometer. Wavetek claims its 3.5-pound device lets engineers troubleshoot the system when they are installing cable-TV and fiber-optic cables to home networks.

According to Wavetek, this mini-OTDR can detect ghosting (multiple internal reflections) and enable users to suppress it. The device achieves a high level of accuracy, thanks to a wide scale of pulse widths that range from 10 nanoseconds to 10 microseconds.

Antec Communications Services in Rolling Meadows, IL, showcased products to help cable operators implement 1550-nm lightwave systems. Its Laser Link 1550 allows an operator to extend a laser link 120 kilometers without repeaters. q

George Lawton writes from Brisbane, CA.

More in Home