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Bandwidth

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.).

By Lee Copeland
October 2, 2000 12:00 PM ET

Computerworld - 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.



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