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
Data transmission and data reception or, more broadly, data communication or digital communications is the transfer and reception of data in the form of a digital bitstream or a digitized analog signal transmitted over a point-to-point or ...
, and
electronics, 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, 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 '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 test
Throughput of a network can be measured using various tools available on different platforms. This page explains the theory behind what these tools set out to measure and the issues regarding these measurements.
Reasons for measuring throughput i ...
s 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
Bandwidth commonly refers to:
* Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range
* Bandwidth (computing), the rate of data transfer, bit rate or thr ...
in hertz and the noise on the channel.
Network consumption
The ''consumed bandwidth'' in bit/s, corresponds to achieved
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 ...
or
goodput, 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,
bandwidth management
Bandwidth management is the process of measuring and controlling the communications (traffic, packets) on a network link, to avoid filling the link to capacity or overfilling the link,https://www.internetsociety.org/wp-content/uploads/2017/08/BWro ...
,
bandwidth throttling
Bandwidth throttling consists in the intentional limitation of the communication speed (bytes or kilobytes per second) of the ingoing (received) data and/or in the limitation of the speed of outgoing (sent) data in a network node or in a network ...
,
bandwidth cap
A data cap, often erroneously referred to as a bandwidth cap, is an artificial restriction imposed on the transfer of data over a network. In particular, it refers to policies imposed by an internet service provider in order to limit customers' u ...
,
bandwidth allocation
Bandwidth allocation is the process of assigning radio frequencies to different applications. The radio spectrum is a finite resource, which means there is great need for an effective allocation process. In the United States, the Federal Commun ...
(for example
bandwidth allocation protocol and
dynamic bandwidth allocation
Dynamic bandwidth allocation is a technique by which traffic bandwidth in a shared telecommunications medium can be allocated on demand and fairly between different users of that bandwidth. This is a form of bandwidth management, and is essential ...
), 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). 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 (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
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 ov ...
(formally ''asymptotic throughput'') for a network is the measure of 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 ...
for a
greedy source A greedy source is a traffic generator in a communication network that generates data at the maximum rate possible and at the earliest opportunity possible. Each source always has data to transmit, and is never in idle state due to congestion avoid ...
, 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 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
In telecommunications, average bitrate (ABR) refers to the average amount of data transferred per unit of time, usually measured per second, commonly for digital music or video. An MP3 file, for example, that has an average bit rate of 128 kbit/ ...
after multimedia
data compression
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 compressio ...
(
source coding), defined as the total amount of data divided by the playback time.
Due to the impractically high bandwidth requirements of uncompressed
digital media, 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
Data compression ratio, also known as compression power, is a measurement of the relative reduction in size of data representation produced by a data compression algorithm. It is typically expressed as the division of uncompressed size by compresse ...
of up to 100:1 compared to uncompressed media.
Web hosting
In
Web hosting service
A web hosting service is a type of Internet hosting service that hosts websites for clients, i.e. it offers the facilities required for them to create and maintain a site and makes it accessible on the World Wide Web. Companies providing web ...
, 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) of common Internet access technologies. For more detailed lists see
*
List of interface bit rates
*
*
Edholm's law
Edholm's law, proposed by and named after Phil Edholm in 2004,
holds that the bandwidth of
telecommunication network
A telecommunications network is a group of nodes interconnected by telecommunications links that are used to exchange messages between the nodes. The links may use a variety of technologies based on the methodologies of circuit switching, mess ...
s double every 18 months, which has proven to be true since the 1970s.
The trend is evident in the cases of
Internet,
cellular (mobile),
wireless LAN and
wireless personal area networks.
The
MOSFET (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 and
Dawon Kahng
Dawon Kahng ( ko, 강대원; May 4, 1931 – May 13, 1992) was a Korean-American electrical engineer and inventor, known for his work in solid-state electronics. He is best known for inventing the MOSFET (metal–oxide–semiconductor field-effe ...
at
Bell Labs in 1959,
and went on to become the basic building block of modern
telecommunications technology.
Continuous
MOSFET scaling, along with various advances in MOS technology, has enabled both
Moore's law (
transistor count
The transistor count is the number of transistors in an electronic device (typically on a single substrate or "chip"). It is the most common measure of integrated circuit complexity (although the majority of transistors in modern microprocessors ...
s in
integrated circuit chips doubling every two years) and Edholm's law (communication bandwidth doubling every 18 months).
References
{{Telecommunications
Network performance
Information theory
Temporal rates