Bandwidth usage is the amount of data transmitted and received by a particular computer or user. The more data exchange that occurs, the higher the potential to clog the network, and the more energy taken up by a particular user. As a result, some companies have caps on bandwidth use which are designed to prevent users from transmitting and receiving so much data that they slow the network down, impairing the experience for other users.
In the case of a computer, bandwidth usage refers to all inbound and outbound traffic. Inbound traffic is data which comes into a computer, as for example when someone downloads a file from a website. Outbound traffic is data which is transmitted by the computer, such as a file attached to an email. Typically, usage is measured in bytes per second (Bps), although other units of measurement may be utilized, and service providers express bandwidth limits in terms of gigabytes, with limits commonly being daily or monthly.
Internet providers track bandwidth usage by looking at the amount of data going through a particular connection, or by identifying specific computers. On a college campus, for example, where people may use their computers in a variety of locations, it is commonly tracked by MAC address, and a student who exceeds the limit will be sent a message. People may be allowed to pay extra for additional bandwidth, or to appeal a usage cap on the argument that they need a lot of bandwidth for specific tasks and projects.
Websites may also have bandwidth usage caps, with the host providing the website's owner with a set amount of bandwidth per month. If traffic to and from the website exceeds this limit, the site may be shut down, or the user may be presented with a bill for the overage. A spike in bandwidth usage can also overload the servers for a website, causing it to go down, as commonly happens when small websites are linked to by large ones.
For people who are interested in or concerned about their bandwidth usage, it is possible to use a bandwidth monitor to keep track. In the case of individuals who have caps on bandwidth usage, a monitor can help to alert the user that service may be cut off in the near future. As a rough frame of reference, something like a streaming movie can take up around two and a half gigabytes, while an email might be two kilobytes.