The term bandwidth in computer networking refers to the data rate supported by a network connection or interface. One most commonly expresses bandwidth in terms of bytes per second (bps). The term comes from the field of electrical engineering, where bandwidth represents the total distance or range between the highest and lowest signals on the communication channel (band).
Network bandwidth is not the only factor that determines the "speed" of a network as perceived by the end user. The other key element of network performance, latency , also affects network applications in important ways.
What is Bandwidth?
Manufacturers of network hardware have done a great job of promoting the concept of bandwidth. Virtually everyone knows the bandwidth rating of their modem or their broadband Internet service. Essentially, bandwidth represents the capacity of the connection, and it's obvious that the greater the capacity, the more likely that greater performance will follow.
Bandwidth can refer to both actual and theoretical throughput, and it is important to distinguish between the two. For example, a V.90 modem supports 56 Kbps of peak bandwidth , but due to limitations of the telephone lines and other factors, it is impossible for a home dial-up network to actually achieve this level. Likewise a Fast Ethernet network theoretically supports 100 Mbps of bandwidth but this level can never be achieved in practical use thanks to overhead in the hardware and in the computer's operating system.
High Bandwidth and Broadband
In the Internet realm, networkers sometimes uses the term high bandwidth to distinguish higher-performing Internet connections from traditional dial-up access speeds. Definitions vary, but high bandwidth connections support data rates of at least 64 Kbps and usually 200 Kbps or 300 Kbps and higher. The definition of high bandwidth differs from the definition of broadband. Technically, the term broadband refers to the method of communication and bandwidth refers to the amount of data that passes through the connection over time.
Measuring Network Bandwidth
A number of tools exist for computer networkers to measure the bandwidth of network connections. On LANs, these tools include netperf and ttcp . On the Internet, numerous "bandwidth test" or "speed test" programs exist, many made available for interactive use through public Web pages. Anyone who uses these programs quickly learns that bandwidth is a highly variable quantity that is difficult to measure precisely. In a nutshell, typical network architectures involve multiple layers hardware and software, as well as time sharing.
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