Chips push data over phone lines
dave powell
A low-cost chipset, known as multipoint broadband access, provides an inexpensive open network interface incorporating switched digital video technology from Allentown, PA-based Broadband Technologies Inc. and 16-carrierless amplitude/ phase, or CAP, modulation encoding and compression technology from AT&T Microelectronics in Durham, NC. The three-chip set enables switched digital video transmission of digital bits of information containing voice, video and data directly to the home over the existing telephone wire from an optical network unit.
The data is transmitted in the form of asynchronous transfer mode, or ATM, cell signals and provides the network with service independence by bringing ATM technology directly to the set-top box. In addition, the chipset reduces the cost of fiber-to-the-curb networks, making it possible for network providers to go aggressively forward with fiber-rich deployments.
AT&T Microelectronics and Broadband Technologies say the chipset transmits audio, data and broadcast-quality video at 51.8 megabits per second into the home or office over existing telephone lines. The chipset can also pull 1.6 Mbits/sec of response signals back into the network. It is installed in both neighborhood optical network units and subscriber set-top boxes and costs $40 to $45 per set. Production quantities are expected in early 1996.
"The chips represent a leap forward in the transport of multiple interactive channels of video and high-speed data over existing phone and cable-TV wiring to homes and businesses," says Gerry Pepenella, transmission integrated circuit marketing director at AT&T Microelectronics.
According to Hamid Lalani, Broadband Technologies` business development manager, "This chipset provides a standard open interface at the set-top [box] that may advance rollout of new interactive services and customer premises equipment."
Precautionary view
However, Ronald O. Brown, a communications consultant from Melrose, MA, cautions: "This technology makes it doubtful if fiber can ever replace copper from the curb to the home. In existing neighborhoods, the labor cost is such that it wouldn`t make sense to install fiber now."
Brown points out, however, that there are valid reasons to run fiber directly into some homes or offices. "In new resorts or real-estate developments, for example, some fiber may be cheaper to install on a per-foot basis," he explains, "but, it wouldn`t be cheaper going up against an installed copper plant...unless the plant is bad.
"Fiber will also have a place in storm-prone areas, such as the Southeast or Southwest. There, fiber`s immunity from electrical interference and power surges promiss to continue to win applications from the curb to the building," Brown says.
A powerful trio
The multipoint broadband access chipset works by combining three technologies, including ATM, CAP signal modulation and switched digital video. The ATM protocol interleaves packets of voice, data and video over common network links. On top of that, CAP signal modulation compresses four-bit data blocks into any one of 16 unique signal "states." Switched digital video sends interactive video or multimedia services across the wire in the 6- to 26-megahert¥frequency band and delivers fiber to the curb. It slips interactive video between the normal frequencies used for voice communications and those used for cable TV.
"This technology is derived from concepts used in high-speed modems, and effectively triples the previous data-transmission capacity of ordinary unshielded twisted-pair cable," claims Pepenella of AT&T Microelectronics.
He notes that within the set-top box, the chips perform the front-end modem function and produce separate Motion Picture Experts Group-2 video and ATM data streams. In cases where ATM cells are delivered to the set, the chips first strip away the CAP coding, feeding the signal into a framing device that strips away the transport bits. A third chip then determines what type of traffic the payload contains and sends each frame to the appropriate output.
At the optical network unit, the chipset handles the framing of the outgoing data, unpacks incoming data and performs the modem function for four switched digital video channels. On the upstream channel, the chips use quadrature phase shift keying modulation, mostly to accommodate data-burst rates.
John Aronsohn, senior analyst for the Yankee Group in Boston, considers this technology "a brilliant idea." He says that "this technology allows the telephone companies to leverage their already existing infrastructure and reduce the cost of installing new networks to carry video."
In a typical application, a multimedia service provider would distribute full-bandwidth data to curbside optical network units. From there, equipment based on the chips would send up to 51.8 Mbits/sec of programming into each subscribing home via 100 to 300 meters of telephone wire. Within each home, this traffic could be split among several telephones and up to six independent personal computers or televisions.
"This feature allows providers to add new digital services over the same transmission facilities and brings fiber`s functionality to the home at a cost approaching ordinary telephone service," says Pepenella. This technology could also enable
Direct ATM data-network access
High-speed, two-way Internet communications
User-controlled video programming
Videoconferencing across campus or metropolitan areas
Companies now supporting or sampling the multipoint broadband access chip technology include France Telecom, AT&T Network Systems, Southwestern Bell, NEC, Fujitsu Network Transmission Systems, Divicom, Philips, Sony, Thomson Consumer Electronics, Zenith and Disney`s Celebration Community. q
Dave Powell writes from Winchester, MA.