Bandwidth refers to the transmission capacity of an electronic-communications line, such as a telephone line, that connects an individual computer to the Internet through a dial-up service provider. Transmission rates are measured by how many bits of data can cross the wire each second. Slower transmission speeds are measured in kilobits per second (1,000 bits, abbreviated K bit/sec. or Kbps), while faster transmissions are in megabits (M bit/sec.) or gigabits (G bit/sec.).

Just as a public utility for gas or water uses metal or plastic pipes to serve your home, an Internet service provider pumps communications bandwidth, or Internet connectivity, into a business or residence via electronic "pipes" such as standard telephone lines, cable connections or dedicated Internet lines.

Technically, bandwidth is a measure of the communications capacity, generally expressed as a rate of how fast data can be stuffed down an Internet pipe.

A rate of 1 kilobit per second (1K bit/sec.) means the line can pass 1,000 bits of data each second. Faster transmissions are measured in megabits per second (M bit/sec.) and now gigabits (G bit/sec.).

You may recall another term, baud, once used to measure modem transmission speeds. Baud refers to how many times the electrical state (voltage or frequency) changes per second, and it was the original unit for measuring telegraph speed. At low speeds, 300 baud is equal to 300 bit/sec. But at higher speeds, a single state change may signal multiple bits, and the correlation fails. The term baud is seldom used anymore.

While bandwidth may be similar to gas and electricity, several flavors of bandwidth are available to business and residential customers.

Most consumers get Internet access through a dial-up service. They connect their telephone lines to the modem port on their PC and then dial the local number of an Internet service provider to reach the Internet. A standard PC modem converts analog phone signals to digital data transmissions for data coming into the PC and vice versa. PC modems deliver bandwidth at transmission speeds of 14.4K bit/sec., 28.8K bit/sec. and 56K bit/sec.

Modem speeds above 56K bit/sec. aren't possible using a standard dial-up connection via a telephone line. The twisted-copper pair wires that make up telephone lines have an upper limit of 56K bit/sec. for analog signals, says Carl Garland, an analyst at Current Analysis Inc. in Sterling, Va. Phone lines consist of "relatively crude copper pairs," he explains. "It's the nature of the quality of that hardware that is responsible for the severe bandwidth limitations of dial-up Internet access."

High-Speed Internet Access

Yet, as the Internet has grown, so have the transmission rates. The way to get around the 56K bit/sec. analog limit is to use digital technology. Several all digital-to-digital connectivity options offer data transmission over the Internet at higher speeds than a dial-up connection.

Individually or collectively, these high-speed access methods are often called broadband. Broadband options include integrated cable modem, T-carrier lines and Digital Subscriber Lines (DSL). Each of these services differs technologically, but all are alike in offering dedicated digital Internet access at 1.5M bit/sec. or faster.

Broadband promises to deliver Internet access speeds anywhere from five to 50 times faster than analog dial-up connections. And the cost is relatively low for cable and DSL access, typically about $40 to $50 per month. T-carrier lines are far more costly. Monthly access charges for T1 service start at approximately $400 per month in most areas, a prohibitive cost for most small businesses and residential customers.

Phone companies have offered an intermediate-level service, called Integrated Services Digital Network (ISDN), that delivers bandwidth up to 128K bit/sec. over a digital-to-digital dial-up connection to the telephone network. ISDN's cost of less than $100 per month once made it affordable for smaller companies and some residential customers, but problems installing and maintaining lines and equipment have hastened ISDN's demise, according to Tere Bracco, an analyst at Current Analysis. "Trying to find someone at a carrier who knew what ISDN was or getting someone to install the line was the stuff of legend," she says. "ISDN is a dial-up backup solution for small and medium-size businesses. There's no reason to choose ISDN if DSL or cable is available."

New Options Available

First introduced by AT&T Corp. in the 1960s, a T-carrier line is the most common type of broadband communication line. A T-carrier point-to-point line consists of four copper wires: one pair to receive data, the other pair to transmit it. The slowest T-carrier line, T1, offers rates of 1.544M bit/sec., but T3 can offer speeds of up to 44.736M bit/sec.

Cable modems [QuickStudy, June 15, 1999] and DSL [QuickStudy, Feb. 27] are also growing in popularity. Adam Guglielmo, an analyst at TeleChoice Inc. in Tulsa, Okla., says the availability of DSL has made broadband access an option for smaller companies and residential customers. "DSL is opening up broadband to small and medium businesses that would have liked to buy T1 or a fractional T1 but found it too expensive," he said.

Dedicated direct PC-to-Web broadband connections also offer convenience. T-carrier lines, cable modems and DSL stay on continuously with no dialing required.

The Yankee Group in Boston forecasts that the residential market for DSL and cable connections will surge from 1.4 million installations last year to 9 million by 2002.

But with increased transmission speeds comes increased risk, says Matthew Kovar, a Yankee Group analyst. "From a security standpoint, broadband is always on, always vulnerable," he says. "It's a shared network infrastructure, like being on one huge [LAN], so anyone who is connected can see into someone else's system."

Copyright © 2000 IDG Communications, Inc.

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