Bandwidth and throughput are two of the most confusing terms used in networking. While we could try to give you a precise definition of each term, it is important that you know how other people might use them and for you to be aware that they are often used interchangeably. First of all, bandwidth is literally a measure of the width of a frequency band. For example, a voice-grade telephone line supports a frequency band ranging from 300 to 3300 Hz; it is said to have a bandwidth of 3300 Hz − 300 Hz = 3000 Hz. If you see the word bandwidth used in a situation in which it is being measured in hertz, then it probably refers to the range of signals that can be accommodated.
When we talk about the bandwidth of a communication link, we normally refer to the number of bits per second that can be transmitted on the link. This is also sometimes called the data rate. We might say that the bandwidth of an Ethernet link is 10 Mbps. A useful distinction can also be made, however, between the maximum data rate that is available on the link and the number of bits per second that we can actually transmit over the link in practice. We tend to use the word throughput to refer to the measured performance of a system. Thus, because of various inefficiencies of implementation, a pair of nodes connected by a link with a bandwidth of 10 Mbps might achieve a throughput of only 2 Mbps. This would mean that an application on one host could send data to the other host at 2 Mbps.
Finally, we often talk about the bandwidth requirements of an application. This is the number of bits per second that it needs to transmit over the network to perform acceptably. For some applications, this might be “whatever I can get”; for others, it might be some fixed number (preferably no more than the available link bandwidth); and for others, it might be a number that varies with time.
Published on Fri 21 May 2010 by Adi Wagstaff in Networking with tag(s): bandwidth throughput