In computing, bandwidth is the maximum rate of data transfer across a given path. Bandwidth may be characterized as network bandwidth, data bandwidth, or digital bandwidth.
This definition of ''bandwidth'' is in contrast to the field of signal processing, wireless communications, modem data transmission,
digital communications, and
electronics
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
, in which ''bandwidth'' is used to refer to analog
signal bandwidth
Bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies. It is typically measured in hertz, and depending on context, may specifically refer to ''passband bandwidth'' or ''baseband bandwidth''. ...
measured in
hertz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...
, meaning the frequency range between lowest and highest attainable frequency while meeting a well-defined impairment level in signal power. The actual bit rate that can be achieved depends not only on the signal bandwidth but also on the noise on the channel.
Network capacity
The term ''bandwidth'' sometimes defines the
net bit rate
In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time.
The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...
'peak bit rate', 'information rate,' or physical layer 'useful bit rate',
channel capacity, or the
maximum throughput
Network throughput (or just throughput, when in context) refers to the rate of message delivery over a communication channel, such as Ethernet or packet radio, in a communication network. The data that these messages contain may be delivered ove ...
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 maximum rate that can be sustained on a link is limited by the
Shannon–Hartley channel capacity for these communication systems, which is dependent on the
bandwidth in hertz and the noise on the channel.
Network consumption
The ''consumed bandwidth'' in bit/s, corresponds to achieved
throughput or
goodput
In computer networks, goodput (a portmanteau of good and throughput) is the application-level throughput of a communication; i.e. the number of useful information bits delivered by the network to a certain destination per unit of time. The amou ...
, i.e., the average rate of successful data transfer through a communication path. The consumed bandwidth can be affected by technologies such as
bandwidth shaping
A network scheduler, also called packet scheduler, queueing discipline (qdisc) or queueing algorithm, is an arbiter on a node in a packet switching communication network. It manages the sequence of network packets in the transmit and receive q ...
,
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 useful data throughput (or
goodput
In computer networks, goodput (a portmanteau of good and throughput) is the application-level throughput of a communication; i.e. the number of useful information bits delivered by the network to a certain destination per unit of time. The amou ...
). For example, 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, much internet traffic uses the
transmission control protocol
The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly ...
(TCP), which requires a three-way handshake for each transaction. Although in many modern implementations the protocol is efficient, it does add significant overhead compared to simpler protocols. Also, data packets may be lost, which further reduces the useful data throughput. In general, for any effective digital communication, a framing protocol is needed; overhead and effective throughput depends on implementation. Useful throughput is less than or equal to the actual channel capacity minus implementation overhead.
Maximum throughput
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 close to the maximum amount.
Asymptotic bandwidths are usually estimated by sending a number of very large messages through the network, measuring the end-to-end throughput. As with other bandwidths, the asymptotic bandwidth is measured in multiples of bits per seconds. Since bandwidth spikes can skew the measurement, carriers often use the 95th
percentile
In statistics, a ''k''-th percentile (percentile score or centile) is a score ''below which'' a given percentage ''k'' of scores in its frequency distribution falls (exclusive definition) or a score ''at or below which'' a given percentage falls ...
method. This method continuously measures bandwidth usage and then removes the top 5 percent.
Multimedia
Digital bandwidth may also refer to:
multimedia bit rate or
average bitrate after multimedia
data compression (
source coding
In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compression ...
), defined as the total amount of data divided by the playback time.
Due to the impractically high bandwidth requirements of uncompressed
digital media
Digital media is any communication media that operate in conjunction with various encoded machine-readable data formats. Digital media can be created, viewed, distributed, modified, listened to, and preserved on a digital electronics device. ' ...
, the required multimedia bandwidth can be significantly reduced with data compression.
The most widely used data compression technique for media bandwidth reduction is the
discrete cosine transform (DCT), which was first proposed by
Nasir Ahmed in the early 1970s.
DCT compression significantly reduces the amount of memory and bandwidth required for digital signals, capable of achieving a
data compression ratio of up to 100:1 compared to uncompressed media.
Web hosting
In
Web hosting service, 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''.
A similar situation can occur for end-user ISPs as well, especially where network capacity is limited (for example in areas with underdeveloped internet connectivity and on wireless networks).
Internet connections
This table shows the maximum bandwidth (the physical layer
net bit rate
In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time.
The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...
) of common Internet access technologies. For more detailed lists see
*
List of interface bit rates
This is a list of interface bit rates, is a measure of information transfer rates, or digital bandwidth capacity, at which digital interfaces in a computer or network can communicate over various kinds of buses and channels. The distinction can ...
*
*
Edholm's law
Edholm's law
Edholm's law, proposed by and named after Phil Edholm, refers to the observation that the three categories of telecommunication, namely wireless (mobile), nomadic (wireless without mobility) and wired networks (fixed), are in lockstep and gradually ...
, proposed by and named after Phil Edholm in 2004,
holds that the bandwidth of
telecommunication networks double every 18 months, which has proven to be true since the 1970s.
The trend is evident in the cases of
Internet
The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
,
cellular
Cellular may refer to:
*Cellular automaton, a model in discrete mathematics
* Cell biology, the evaluation of cells work and more
* ''Cellular'' (film), a 2004 movie
*Cellular frequencies, assigned to networks operating in cellular RF bands
*Cell ...
(mobile),
wireless
Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points without the use of an electrical conductor, optical fiber or other continuous guided medium for the transfer. The most ...
LAN
Lan or LAN may also refer to:
Science and technology
* Local asymptotic normality, a fundamental property of regular models in statistics
* Longitude of the ascending node, one of the orbital elements used to specify the orbit of an object in sp ...
and
wireless personal area networks.
The
MOSFET
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
(metal-oxide-semiconductor field-effect transistor) is the most important factor enabling the rapid increase in bandwidth.
The MOSFET (MOS transistor) was invented by
Mohamed M. Atalla
Mohamed M. Atalla ( ar, محمد عطاالله; August 4, 1924 – December 30, 2009) was an Egyptian-American engineer, physicist, cryptographer, inventor and entrepreneur. He was a semiconductor pioneer who made important contributions to ...
and
Dawon Kahng at
Bell Labs
Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984),
then AT&T Bell Laboratories (1984–1996)
and Bell Labs Innovations (1996–2007),
is an American industrial research and scientific development company owned by mult ...
in 1959,
and went on to become the basic building block of modern
telecommunications
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...
technology.
Continuous
MOSFET scaling
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
, along with various advances in MOS technology, has enabled both
Moore's law
Moore's law is the observation that the number of transistors in a dense integrated circuit (IC) doubles about every two years. Moore's law is an observation and projection of a historical trend. Rather than a law of physics, it is an empir ...
(
transistor counts in
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
chips doubling every two years) and Edholm's law (communication bandwidth doubling every 18 months).
References
{{Telecommunications
Network performance
Information theory
Temporal rates