Editing Internet access (section)

===Network congestion===
Users may share access over a common network infrastructure. Since most users do not use their full connection capacity all of the time, this aggregation strategy (known as [[contended service]]) usually works well, and users can burst to their full data rate at least for brief periods. However, [[peer-to-peer]] (P2P) [[file sharing]] and high-quality streaming video can require high data-rates for extended periods, which violates these assumptions and can cause a service to become oversubscribed, resulting in congestion and poor performance. The TCP protocol includes flow-control mechanisms that automatically throttle back on the bandwidth being used during periods of [[network congestion]]. This is fair in the sense that all users who experience congestion receive less bandwidth, but it can be frustrating for customers and a major problem for ISPs. In some cases, the amount of bandwidth actually available may fall below the threshold required to support a particular service such as video conferencing or streaming live video–effectively making the service unavailable.

When traffic is particularly heavy, an ISP can deliberately throttle back the bandwidth available to classes of users or for particular services. This is known as [[traffic shaping]] and careful use can ensure a better [[quality of service]] for time critical services even on extremely busy networks. However, overuse can lead to concerns about fairness and [[network neutrality]] or even charges of [[censorship]], when some types of traffic are severely or completely blocked.