Incomputing,bandwidth is the maximum rate of data transfer across a given path. Bandwidth may be characterized asnetwork bandwidth,[1]data bandwidth,[2] ordigital bandwidth.[3][4]
This definition ofbandwidth is in contrast to the field ofsignal processing,wireless communications,modem data transmission,digital communications, andelectronics,[citation needed] in whichbandwidth is used to refer to thesignal bandwidth measured inhertz, 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 thenoise on the channel.
The termbandwidth sometimes defines thenet bit ratepeak bit rate,information rate, or physical layeruseful bit rate,channel capacity, or themaximum 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 maximum rate that can be sustained on a link is limited by theShannon–Hartley channel capacity for these communication systems, which is dependent on thebandwidth in hertz and the noise on the channel.
Theconsumed bandwidth in bit/s corresponds to achievedthroughput orgoodput, i.e., the average rate of successful data transfer through a communication path. The consumed bandwidth can be affected by technologies such asbandwidth shaping,bandwidth management,bandwidth throttling,bandwidth cap,bandwidth allocation (for examplebandwidth allocation protocol anddynamic 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). For example, a channel withx bit/s may not necessarily transmit data atx rate, since protocols, encryption, and other factors can add appreciable overhead. For instance, much internet traffic uses thetransmission control protocol (TCP), which requires athree-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.
Theasymptotic bandwidth (formallyasymptotic throughput) for a network is the measure of maximum throughput for agreedy source, for example when the message size (the number of packets per second from a source) approaches close to the maximum amount.[5]
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 95thpercentile method. This method continuously measures bandwidth usage and then removes the top 5 percent.[6]
Digital bandwidth may also refer to:multimedia bit rate oraverage bitrate after multimediadata compression (source coding), defined as the total amount of data divided by the playback time.
Due to the impractically high bandwidth requirements of uncompresseddigital media, the required multimedia bandwidth can be significantly reduced with data compression.[7] The most widely used data compression technique for media bandwidth reduction is thediscrete cosine transform (DCT), which was first proposed byNasir Ahmed in the early 1970s.[8] DCT compression significantly reduces the amount of memory and bandwidth required for digital signals, capable of achieving adata compression ratio of up to 100:1 compared to uncompressed media.[9]
Inweb hosting service, the termbandwidth is often used to describe the amount of data transferred to or from the website or server within a prescribed period of time, for examplebandwidth consumption accumulated over a month measured in gigabytes per month.[citation needed][10] The more accurate phrase used for this meaning of a maximum amount of data transfer each month or given period ismonthly data transfer.[citation needed]
A similar situation can occur for end-userInternet service providers as well, especially where network capacity is limited (for example in areas with underdeveloped internet connectivity and on wireless networks).
| Bit rate | Connection type |
|---|---|
| 56 kbit/s | Dial-up |
| 1.5 Mbit/s | ADSL Lite |
| 1.544 Mbit/s | T1/DS1 |
| 2.048 Mbit/s | E1 /E-carrier |
| 4 Mbit/s | ADSL1 |
| 10 Mbit/s | Ethernet |
| 11 Mbit/s | Wireless802.11b |
| 24 Mbit/s | ADSL2+ |
| 44.736 Mbit/s | T3/DS3 |
| 54 Mbit/s | Wireless802.11g |
| 100 Mbit/s | Fast Ethernet |
| 155 Mbit/s | OC3 |
| 600 Mbit/s | Wireless802.11n |
| 622 Mbit/s | OC12 |
| 1 Gbit/s | Gigabit Ethernet |
| 1.3 Gbit/s | Wireless802.11ac |
| 2.5 Gbit/s | OC48 |
| 5 Gbit/s | SuperSpeed USB |
| 7 Gbit/s | Wireless802.11ad |
| 9.6 Gbit/s | OC192 |
| 10 Gbit/s | 10 Gigabit Ethernet,SuperSpeed USB 10 Gbit/s |
| 20 Gbit/s | SuperSpeed USB 20 Gbit/s |
| 40 Gbit/s | Thunderbolt 3 |
| 100 Gbit/s | 100 Gigabit Ethernet |
Edholm's law, proposed by and named after Phil Edholm in 2004,[11] holds that the bandwidth oftelecommunication networks double every 18 months, which has proven to be true since the 1970s.[11][12] The trend is evident in the cases ofInternet,[11]cellular (mobile),wireless LAN andwireless personal area networks.[12]
TheMOSFET (metal–oxide–semiconductor field-effect transistor) is the most important factor enabling the rapid increase in bandwidth.[13] The MOSFET (MOS transistor) was invented byMohamed M. Atalla andDawon Kahng atBell Labs in 1959,[14][15][16] and went on to become the basic building block of moderntelecommunications technology.[17][18] ContinuousMOSFET scaling, along with various advances in MOS technology, has enabled bothMoore's law (transistor counts inintegrated circuit chips doubling every two years) and Edholm's law (communication bandwidth doubling every 18 months).[13]
