The race for bandwidth: phone and cable companies fight an uphill battle. (Technology Information)

As demand for data bandwidth rises, the information superhighway's infrastructure is struggling to keep up. In an Internet-mad world where 28.8-Kbps modems and even 128-Kbps ISDN lines no longer seem fast, both telephone and cable companies are racing to offer higher-speed data connections. But despite all the hype you've been hearing, don't expect to find a fast, cheap connection anytime soon.

Within the next couple of years, phone companies plan to offer several kinds of DSL (digital subscriber line) connections using the ordinary copper phone lines that already run into your home or office. You'll even be able to make a voice call and a DSL connection simultaneously on the same line. High-bit-rate DSL (HDSL) will run at 384 Kbps bidirectionally; asymmetric DSL (ADSL) will initially run at 1.544 Mbps downstream from the phone company to you, and 64 Kbps upstream from you to the phone company. Later versions of ADSL should run at up to 6 Mbps downstream and 640 Kbps upstream.

Phone versus Cable

DSL will compete with the much-ballyhooed cable modem the cable TV companies want to offer for Internet connections.

A cable modem works very differently from a phone line. Instead of using a dedicated connection, all the cable subscribers in a region will share an Internet feed, occupying the equivalent of one cable television channel. Each data packet will contain a user ID, and your cable modem will pick out only those packets addressed to you.

The system resembles a local area network, and many proposed cable modems use an Ethernet-like protocol. A major drawback is that today's cables can carry only downstream data; for upstream data, you'll have to tie up a phone line, or the companies will have to build a wireless radio network.

Bandwidth Not Enough

Although cable companies talk about 500-Kbps to 5-Mbps or even faster connections, each cable modem subscriber will get only a fraction of that bandwidth. When fewer users are logged on, more bandwidth may be available.

But a faster final link doesn't always mean faster performance. Data speeds--whether for DSL service or for cable modem--describe only the last downstream link to your computer. Actual data speed depends on many other factors, such as the servers and intermediate links.

DSL, like your phone service, lets you switch between different providers. But since cable modems--like cable television--work only with data fed by the local cable company, they can't offer that option. Cable companies can't provide true switched operation or upstream connection without replacing their present cables and electronics, a process that would take many years, if it is ever done.

US West, one of the regional Bell companies, says it will provide DSL service in some cities next year and that by 1998 DSL will be widely available, with rates starting at about $35 per month for metered service. But because it needs high-quality, relatively short wire runs, DSL won't be available in all areas; it cannot reach as far as ISDN.

DSL Has the Edge

Don't expect the cable TV companies to settle on a standard cable modem format in less than two years, because no one knows what will work with today's myriad cable systems. Therefore, many companies are likely to use interim formats that may quickly vanish once a standard finally emerges.

For now, the phone companies appear better situated, since they can offer limited DSL services without rebuilding their networks, though widespread use of DSL will require newer switching equipment. Cable companies face greater obstacles, because their systems aren't designed for two-way transfer, and data customers are much more demanding than TV viewers.

The 6-Mbps data rates later versions of ASDL promise should meet most users' needs for some years to come. Then we'll stop complaining about slow modems and find other bottlenecks to gripe about.