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Look up Bandwidth in Wiktionary, the free dictionary.

In computer networking and computer science, digital bandwidth, network bandwidth or just bandwidth is a measure of available or consumed data communication resources expressed in bit/s or multiples of it (kbit/s, Mbit/s etc).

Bandwidth may refer to bandwidth capacity or available bandwidth in bit/s, which typically means the net bit rate, channel capacity or the maximum throughput of a logical or physical communication path in a digital communication system. For example, bandwidth test implies measuring 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, radio bandwidth or analog bandwidth, the last especially in computer networking literature.

Bandwidth may also refer to consumed bandwidth (bandwidth consumption), corresponding to achieved throughput or goodput, i.e. average data rate of successful data transfer through a communication path. This meaning is for example used in expressions such as bandwidth shaping, bandwidth management, bandwidth throttling, bandwidth cap, bandwidth allocation (for example bandwidth allocation protocol and dynamic bandwidth allocation), etc. An explanation to this usage is that digital bandwidth of a bit stream 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.

Digital bandwidth may also refer to: average bitrate (ABR) after multimedia data compression (source coding), defined as the total amount of data divided by the playback time.

Some authors prefer less ambiguous terms such as gross bit rate, net bit rate, channel capacity and throughput, to avoid confusion between digital bandwidth in bits per second and analog bandwidth in hertz.

Contents 1 Bandwidth in web hosting 2 Internet connection bandwidths 3 See also 4 References

[edit] Bandwidth in web hosting

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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 Gigabyte 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.

Consider this example:

• Rented Water Tank = web-server that hosts your website,
• Water company = hosting company where your web-server resides,
• Water = files, data, images, etc. that comprise your website,
• Pipe = the internet,
• Quantity of water delivered = bandwidth consumption,
• You = patron / visitor of your website which is hosted on aforementioned web-server.

There's a pipe that delivers water from your rented water tank to your home. As you request water, the water company delivers it to you. All the while, they are keeping track of how much water was delivered to you, during a billing cycle. You have a contract with the water company in which they agree to charge you a fixed dollar amount per billing cycle, provided you do not request more water than the allowable quantity, as defined in your contract. If you do request more water, they will not deny you ... but you will incur additional charges for the extra water requested / delivered.

With that example in mind, web-pages typically equate to a small quantity of water ... while images, videos, PDFs and other similar media can potentially equate to large quantities of water being delivered by your water company. The accumulated total can grow rather quickly, especially when your website is popular / visited by many people.

[edit] Internet connection bandwidths

Below is a table showing the maximum bandwidth (the physical layer net bitrate, often slightly more than the maximum throughput) of common Internet access technologies. For a more detailed list see List of device bandwidths.

56 kbit/s	Modem / Dialup
1.5 Mbit/s	ADSL Lite
1.544 Mbit/s	T1
10 Mbit/s	Ethernet
11 Mbit/s	Wireless 802.11b
44.736 Mbit/s	T3
54 Mbit/s	Wireless-G 802.11g
100 Mbit/s	Fast Ethernet
155 Mbit/s	OC3
300 Mbit/s	Wireless-N 802.11n
622 Mbit/s	OC12
1000 Mbit/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

[edit] See also

• 92 Code
• Bandwidth cap
• Bandwidth extension
• Bandwidth optimization
• Bandwidth test
• Bandwidth theft
• Bit rate
• Broadband
• Comparison of latency and throughput
• Goodput
• List of device bandwidths
• Measuring network throughput
• Narrowband
• Signal processing
• Throughput

[edit] References