Design Features

ADSL: the end of the wait for home Internet?

Stephen Kempainen, Technical Editor

Accessing the Internet from home can be a drag: Long access times make for a slow, tedious process. But new DSL technology may bring relief for bored commuters on the information highway.

  Surfing the Web from home is something like commuting during rush hour: You travel in bursts, pauses, and then slow motion while the traffic—not of cars and trucks, but of bits and bytes—trickles along. In fact, some impatient people even call the World Wide Web the "World Wide Wait." But there is light at the end of the tunnel for commuters on the Internet highway. Regional Bell operating companies (RBOCs) and telephone-service providers have been working on ways to accelerate Internet access by speeding transmission over the last mile of copper twisted-pair wire in the plain-old telephone system (POTS) before that wire enters your home.

  Among technologies attempting to break the Internet gridlock are cable modems, fiber-hybrid coaxial cable, wireless cable, satellite feeds, and digital subscriber line (DSL). Perhaps the most promising of these technologies is DSL, because it uses your phone's copper twisted-pair wiring to provide 8-Mbps downstream communication links. With no more than

8,000 ft of twisted-pair wire now connecting approximately 650 million customers worldwide to the Public Switched Telephone Network (PSTN), a technology using existing cable offers a distinct advantage. On the other hand, DSL technologies resemble car dealerships in that their proponents continually tout their own approaches as the best fast-Internet provider. Adding to the controversy, the technologies' names—asymmetric DSL (ADSL); high-bit-rate DSL (HDSL); symmetric DSL (SDSL); rate-adaptive DSL (RADSL); very high-data-rate DSL (VDSL), 384DSL; and integrated services digital network (ISDN)—cook up a confusing alphabet soup. Even within ADSL there are two competing means of achieving the same goal. Table 1 attempts to differentiate the various technologies.

  The RBOCs are now providing Internet access to homes through POTS and 28.8-kbps modems. However, RBOCs want to get Internet users off the central-office switch, because they are tying it up at only $11.25/month with connections that can last for hours. The RBOCs would like DSL service to have happened yesterday, but, to implement it, they must install modems and POTS splitters. Toward that end, all seven RBOCs and most telephone-service providers worldwide are involved in ADSL tests and trials, with some planning commercial deployment by the end of this year. Meanwhile, because ISDN is available now, the RBOCs are deploying it in an attempt to fill the need for bandwidth. But many service providers view ISDN as an old, slow technology that will not become pervasive.

  Says one RBOC representative, "We will not market another four-letter acronym to the public. The customer wants fast Internet service; most don't care about the underlying technology." So, you probably won't see any DSL marketing to consumers from phone companies. Instead, they'll try to sell you a service for "no-wait" Internet access at x dollars a month.

  What that no-wait service will be remains to be seen. Perhaps the most promising contender is ADSL, which its designers conceived for video-on-demand (VoD) delivery over the POTS line. Many vendors are providing ADSL chips that promise to provide low-cost modem implementations (Table 2). By using highly integrated DSP, error correction, and signal conditioning, these new chip sets can achieve multimegabit information delivery through the DSL (see box, "Upgrading twisted pair to multimegabit service").