In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measurement of bit-rate of available or consumed data communication resources expressed in bits per second or multiples of it (bit/s, kbit/s, Mbit/s, Gbit/s, etc.).
Note that in textbooks on signal processing, wireless communications, modem data transmission, digital communications, electronics, etc., the word 'bandwidth' is used to refer to analog signal bandwidth measured in hertz. The connection is that according to Hartley's law, the digital data rate limit (or channel capacity) of a physical communication link is proportional to its bandwidth in hertz.
Network bandwidth capacity 
Bandwidth sometimes defines the net bit rate (aka. peak bit rate, information rate or physical layer useful bit rate), channel capacity, or the maximum throughput of a logical or physical communication path in a digital communication system. For example, bandwidth tests measure the maximum throughput of a computer network. The reason for this usage is that according to Hartley's law, the maximum data rate of a physical communication link is proportional to its bandwidth in hertz, which is sometimes called frequency bandwidth, spectral bandwidth, RF bandwidth, signal bandwidth or analog bandwidth.
Network bandwidth consumption 
Bandwidth in bit/s may also refer to consumed bandwidth, corresponding to achieved throughput or goodput, i.e., the average rate of successful data transfer through a communication path. This sense applies to concepts and technologies such as bandwidth shaping, bandwidth management, bandwidth throttling, bandwidth cap, bandwidth allocation (for example bandwidth allocation protocol and dynamic bandwidth allocation), etc. A bit stream's bandwidth is proportional to the average consumed signal bandwidth in Hertz (the average spectral bandwidth of the analog signal representing the bit stream) during a studied time interval.
Channel bandwidth may be confused with data throughput. A channel with x bps may not necessarily transmit data at x rate, since protocols, encryption, and other factors can add appreciable overhead. For instance, a lot of internet traffic uses the transmission control protocol (TCP) which requires a three-way handshake for each transaction, which, though in many modern implementations is efficient, does add significant overhead compared to simpler protocols. In general, for any effective digital communication, a framing protocol is needed; overhead and effective throughput depends on implementation. Actual throughput is less than or equal to the actual channel capacity plus implementation overhead.
Asymptotic bandwidth 
The asymptotic bandwidth (formally asymptotic throughput) for a network is the measure of maximum throughput for a greedy source, for example when the message size (the number of packets per second from a source) approaches infinity.
Asymptotic bandwidths are usually estimated by sending a number of very large messages through the network, measuring the end-to-end throughput. As other bandwidths, the asymptotic bandwidth is measured in multiples of bits per second.
Multimedia bandwidth 
Bandwidth in web hosting 
In website hosting, the term "bandwidth" is often incorrectly used to describe the amount of data transferred to or from the website or server within a prescribed period of time, for example bandwidth consumption accumulated over a month measured in gigabytes per month. The more accurate phrase used for this meaning of a maximum amount of data transfer each month or given period is monthly data transfer.
Internet connection bandwidths 
This table shows the maximum bandwidth (the physical layer net bitrate) of common Internet access technologies. For more detailed lists see
|56 kbit/s||Modem / Dialup|
|1.5 Mbit/s||ADSL Lite|
|2.048 Mbit/s||E1 / E-carrier|
|11 Mbit/s||Wireless 802.11b|
|54 Mbit/s||Wireless 802.11g|
|100 Mbit/s||Fast Ethernet|
|600 Mbit/s||Wireless 802.11n|
|1 Gbit/s||Gigabit Ethernet|
|10 Gbit/s||10 Gigabit Ethernet|
|100 Gbit/s||100 Gigabit Ethernet|
See also 
- Andrew S. Tanenbaum Computer networks, Prentice Hall PTR, 2003
- Douglas Comer, Computer Networks and Internets , page 99 ff, Prentice Hall 2008.
- Fred Halsall, Introduction to data communications and computer networks, page 108, Addison-Wesley, 1985.
- Cisco Networking Academy Program: CCNA 1 and 2 companion guide, Volym 1–2, Cisco Academy 2003
- Behrouz A. Forouzan, Data communications and networking, McGraw-Hill, 2007
- Modeling Message Passing Overhead by C.Y Chou et al. in Advances in Grid and Pervasive Computing: First International Conference, GPC 2006 edited by Yeh-Ching Chung and José E. Moreira ISBN 3540338098 pages 299-307