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.).
This is in contrast to the use of the term bandwidth in the field of
signal processing. In textbooks on signal processing, wireless
communications, modem data transmission, digital communications,
electronics, etc., bandwidth is used to refer to analog signal bandwidth
measured in hertz. The connection to the computing term 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
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)
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 seconds.
Digital bandwidth may also refer to: multimedia bit rate or average
bitrate after multimedia data compression (source coding), defined as
the total amount of data divided by the playback time.
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
Internet connection bandwidths
This table shows the maximum bandwidth (the physical layer net bitrate) of common Internet access technologies.
56 kbit/s Modem / Dialup
1.5 Mbit/s ADSL Lite
1.544 Mbit/s T1/DS1
2.048 Mbit/s E1 / E-carrier
10 Mbit/s Ethernet
11 Mbit/s Wireless 802.11b
44.736 Mbit/s T3/DS3
54 Mbit/s Wireless 802.11g
100 Mbit/s Fast Ethernet
155 Mbit/s OC3
600 Mbit/s Wireless 802.11n
622 Mbit/s OC12
1 Gbit/s Gigabit Ethernet
2.5 Gbit/s OC48
9.6 Gbit/s OC192
10 Gbit/s 10 Gigabit Ethernet
100 Gbit/s 100 Gigabit Ethernet
1. Andrew S. Tanenbaum Computer networks, Prentice Hall PTR, 2003.
2. Douglas Comer, Computer Networks and Internets , page 99 ff, Prentice Hall 2008.
3. Fred Halsall, Introduction to data communications and computer networks, page 108, Addison-Wesley, 1985.
4. Cisco Networking Academy Program: CCNA 1 and 2 companion guide, Volym 1–2, Cisco Academy 2003.
5. Behrouz A. Forouzan, Data communications and networking, McGraw-Hill, 2007.
6. Chou, C. Y.; et al. (2006). "Modeling Message Passing Overhead". In Chung, Yeh-Ching; Moreira, Jose E. Advances in Grid and Pervasive Computing: First International Conference, GPC 2006. pp. 299–307. ISBN 3540338098.
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