What is Bandwidth?

In computer networking, the ugly term 'Bandwidth' refers to the measure of the capacity of a medium to transmit data. A medium that has a high capacity, for example, has a high bandwidth, whereas a medium that has limited capacity has a low bandwidth. Bandwidth can be best understood by using an analogy to water hoses. If a half-inch garden hose can carry water-flow from a trickle up to two gallons per minute, then that hose can be said to have a bandwidth of two gallons per minute. A four-inch fire hose, however, might have a bandwidth that exceeds 100 gallons per minute. Data transmission rates frequently are stated in terms of the bits that can be transmitted per second. An Ethernet LAN theoretically can transmit 10 millions bits per second and has a bandwidth of 10 megabits per seconds (Mbps). The bandwidth that a cable can accommodate is determined in part part by the cable's length. A short cable generally can accommodate greater bandwidth than a long cable, which is one reason all cable designs specify maximum lengths for cable runs. Beyond those limits, the highest-frequency signals can deteriorate, and errors begin to occur in data signals.

NOTE: The term 'bandwidth' also has another meaning. In the communications industry, bandwidth refers to the range of the available frequencies between the lower frequency limit and the upper frequency limit. Frequencies are measured in Hertz (Hz), or cycles per second. The bandwidth of a voice telephone line is 400 - 4,000 Hz, which means that the line can transmit signals with frequencies ranging from 400 to 4,000 cycles per second.

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