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Battle Lines: How the telephone and cable pipelines differ
Sunday, April 04, 1999 By Ken Zapinski, Post-Gazette Staff Writer
Connecting to the Future
First in an occasional series
In a drab brick building in Squirrel Hill, a bank of flashing green lights signal the start of a new computer age. They represent residential customers using Bell Atlantic Corp.'s new high-speed data service to forge round-the-clock links to the Internet at speeds 10 times, 25 times, even 100 times faster than the fastest dial-up modems.
Across town in Sheraden, in what could pass for a warehouse, high-tech electronics are doing the same for customers of AT&T's Broadband & Internet Services unit.
Telephone companies and cable television companies have had different hurdles to overcome in trying to transform their "ancient" networks to handle the data needs of today's computerized online world.
Bell Atlantic is figuring out how to cram oceans of data down a commonplace copper telephone line.
AT&T, meanwhile, is turning the television cables they acquired when they bought Tele-Communications Inc. last month into highways of two-way communication.
Despite the technological tweaking, both networks have their limitations.
Bell Atlantic has been slower out of the gate even though its asynchronous digital subscriber line, or ADSL, technology, which was developed with an eye toward delivering video over phone lines, dates back to the 1970s..
A simple phone call uses less than one-half of 1 percent of the capacity on the pair of thin copper wires that make up the line leading to every home telephone. That capacity remained unused for years because the phone company had no way to transport so much information through the rest of the phone network using old-style copper cables.
The advent of electronic switches and fiber-optic cables, which can carry far more information than their copper counterparts, began to change that two decades ago.
OnOnly recently, according to Bell Atlantic officials, has the demand for high-speed data connections increased enough and the cost of equipment dropped enough to make ADSL economically feasible. "We've had some false starts," said Jeff Waldhuter, Bell Atlantic's director of technology and engineering.
Bell Atlantic began offering its ADSL InfoSpeed service last fall in Squirrel Hill, Oakland, Bethel Park, Glenshaw, Greensburg and several other locations in Western Pennsylvania.
To understand how it works, imagine a Squirrel Hill customer who decides to spend some time surfing the Web while chatting with his mother on the phone.
His computer's request for www.post-gazette.com, the Post-Gazette's home page, travels through a special DSL modem and out of the house through a new, computer-only telephone line. Meanwhile, the phone conversation runs through a filter that prevents the data flow from interfering with the audio.
The data and voice then join up on the line that runs from the house to the telephone pole and down the street. Like the 18,000 other telephone lines in Squirrel Hill, it stretches all the way to the Bell Atlantic's switching office at the corner of Murray Avenue and Pocusset Street. The data can travel as fast as 7.1 million bits per second (7.1 Mbps), compared to the 56,000 bits per second (56 kbps) speed of the fastest dial-up modems.
Once inside the building, the call to Mom and the web-page request part ways. The voice traffic moves through a voice switch and is sent on its way to Mom's house.
The computer request, meanwhile, goes into a data funnel of sorts called a digital subscriber line access multiplexer. The DSLAM, as it is called, channels the information onto a high-capacity fiber-optic ring which carries it to the phone company's asynchronous transfer mode (ATM) switch located Downtown.
The switch sends the data to its proper location. Carnegie Mellon University, for instance, has arranged with Bell Atlantic to make an ADSL connection directly into its campus network for students and staff. For other customers, the connection might into their office network. For most, the connection will be to BellAtlantic.net, Stargate, America Online or some other Internet service provider for a quick trip to the Internet.
Bill Isler of Squirrel Hill began receiving ADSL service for free more than a year ago as part of a Bell Atlantic trial. When that ended in September, he gladly coughed up the $60 a month to keep his hookup.
"We did not want to go back to the previous Internet folks we had before," Isler said. "The speed is phenomenal."
That is, if you can get it. Because the data signals break down the farther they have to travel down the copper line, only customers within three miles of their local switching office can get the ADSL service. The physical quality of the line can affect the service as well.
Line quality was also key for TCI, which began offering cable modem data service to its Pittsburgh-area customers last summer, around the time it agreed to merge with AT&T. The data service is offered through @Home, an Internet access corporation controlled by AT&T.
When cable systems were originally built, they used metal coaxial cable to carry the television signals from their satellite receiving stations out to neighborhoods. That sort of network needs amplifiers every few thousand feet to boost the signal and send it farther down the line. But each amplification distorts the quality of the signal a little bit. And if one of the amplifiers breaks down, all service farther down the line is lost.
To make the data system work, TCI (now AT&T Broadband & Internet Services) must replace those neighborhood feeder cables with fiber-optic cables, which use laser-fired light pulses to transmit data. Sophisticated electronics are also needed to turn the one-way television system into a two-way system in which computer data and television programming can travel side by side.
About a quarter of the old TCI system has been converted to fiber-optics. The system in Pittsburgh has not, but company officials expect to rewire the city within the next two years.
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Understanding ADSL