Bandwidth is a term used to describe the amount of information that can be transmitted over a connection. It is usually given as bits per second, or as some larger denomination of bits, such as Megabits per second, expressed as kbit/s or Mbit/s. Bandwidth is a raw measurement that considers the total amount of data transferred in a given period of time as a rate, without regard to the quality of the signal itself.
Bandwidth is a measure of how much information can be transferred over a connection.
Throughput can be seen as a subset of bandwidth that takes into account whether the data was transmitted successfully or not. Although the bandwidth of a connection can be quite high, if the signal loss is also high, the throughput of the connection will remain somewhat low. On the other hand, even a relatively low bandwidth connection can have a moderately high throughput if the signal quality is also high.
Uploading multiple images or downloading significant amounts of data at once can consume enough bandwidth to slow down an Internet connection.
Bandwidth is more familiar to consumers due to its usage by hosting companies or Internet service providers. The sense in which it is used by most hosting companies, i.e. as a measure of the total data transferred in a month, is not strictly correct. This measure is more correctly called data transfer, but the use of bandwidth by hosting companies is so widespread that it has become accepted by the general public.
Many hosting providers limit the amount of bandwidth a website can transfer in a given period, usually a month, but sometimes 24 hours or a week. If the site exceeds its quota, the service is usually suspended or the additional bandwidth is billed separately, often at a much higher cost than the basic cost included in the hosting plan.
Some hosts offer so-called unlimited plans, which in theory have an unlimited amount of data transfer per month. Typically, the actual bandwidth, i.e. the transfer per second of a connection, is somewhat limited on these services, ensuring that the data transfer to the website never becomes too large. If the limit is reached, users’ speeds may be reduced substantially or service may even be interrupted.
Different technologies for connecting to the Internet also have different bandwidth limits associated with them. They act as an upper limit on how much data can be transferred each second by a user. At the lower end of the spectrum, a simple dial-up connection, using a modem and a regular phone line, has a maximum of about 56 kbit/s. In comparison, a DSL connection can reach almost 10 Mbit/s, or two hundred times more than a dial-up connection, while a cable connection can theoretically reach around 30 Mbit/s. Connections such as a T1 line can reach 1.544 Mbit/s, but due to their dedicated nature, the actual bandwidth they achieve is generally higher than cable or DSL. Larger connections include T3 at around 43 Mbit/s, OC3 at 155 Mbit/s, OC12 at 622 Mbit/s and the monumental OC192 at 9.6 Gbit/s, over three hundred times faster than a cable connection as its speed maximum .
Bandwidth is also a limiting factor for the technology that connects the computer itself to the modem or device that interacts with the Internet hotline. Basic Ethernet, for example, has a bandwidth of 10 Mbit/s, so using an internet connection faster than that would be a huge loss in speed. Fast Ethernet hits 100Mbit/s, more than fast enough for all consumer uses, while Gigabit Ethernet can reach 1Gbit/s and 10Gbit Ethernet is 10Gbit/s. Wireless technologies are also limited by bandwidth, with Wireless 802.11b boasting 11 Mbit/s, Wireless-G 802.11g with a 54 Mbit/s cap, and Wireless-N 802.11na at 300 Mbit/s.
Supporters of net neutrality think government legislation is needed to prevent internet service providers from throttling bandwidth for paying customers.