For digital devices, the bandwidth

Bandwidth refers to the data transmission capacity of a communications channel. The greater a channel's bandwidth, the more information it can carry per unit of time.

The term technically refers to the range of frequencies that a channel can carry. The higher the frequency, the higher the bandwidth and thus the greater the capacity of a channel. This capacity might more appropriately be referred to as throughput.

For digital devices, the bandwidth is usually expressed in bits per second (bps), kilobits per second (kbps) or megabits per second (mbps). For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).

The required bandwidth can vary greatly according to the type of application. For example, the transmission of simple ASCII text messages requires relatively little bandwidth, whereas the transmission of high resolution video images requires a large amount of bandwidth.

A major trend in networks at all levels (i.e., from LANs to the Internet) has been increasing bandwidth. This has been a result of technological advances with regard to both the transmission media and the devices that are used with it, such as transmission circuits, reception circuits and routers. For example, the development of optical fiber cable made possible a huge increase in bandwidth as compared with copper wire cable, and the bandwidth of optical fiber cable continued to increase both as a result of improvements to the optical fiber itself and to the transmitters and other devices used with it.

Nevertheless, bandwidth is often insufficient. This is due to such factors as the continued increase in the numbers of users (especially of the Internet), the growth in the demand for applications which require more bandwidth and the high cost of upgrading some portions of networks (particularly replacing copper wire connections to individual homes and offices with optical fiber). Thus, an important principle in the design of network protocols continues to be the conservation of bandwidth.