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Reliability (computer networking)
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<p> In <a href="/facts/Computer_networking/3w5RM99p">computer networking</a>, a reliable protocol is a <a href="/facts/Communication_protocol/5uady7cB">communication protocol</a> that notifies the sender whether or not the delivery of data to intended recipients was successful. <a href="/facts/Reliability_engineering/cd6AS5w3">Reliability</a> is a synonym for assurance, which is the term used by the <a href="/facts/ITU/xnT5QSEl">ITU</a> and <a href="/facts/ATM_Forum/0Mr202cm">ATM Forum</a>, and leads to <a href="/facts/Fault-tolerant/rasrYlJk">fault-tolerant</a> messaging. </p><p>Reliable protocols typically incur more overhead than unreliable protocols, and as a result, function more slowly and with less scalability. This often is not an issue for <a href="/facts/Unicast/PHStTfFe">unicast</a> protocols, but it may become a problem for <a href="/facts/Reliable_multicast/URHHI2Hw">reliable multicast</a> protocols. </p><p><a href="/facts/Transmission_Control_Protocol/WW4sPrt9">Transmission Control Protocol</a> (TCP), the main protocol used on the <a href="/facts/Internet/Xw1rVvJU">Internet</a>, is a reliable unicast protocol; it provides the abstraction of a <a href="/facts/Reliable_byte_stream/YbSblvM5">reliable byte stream</a> to applications. <a href="/facts/User_Datagram_Protocol/dxLU0D6q">UDP</a> is an unreliable protocol and is often used in <a href="/facts/Computer_games/AEDr23gA">computer games</a>, <a href="/facts/Streaming_media/4rPhSq0Y">streaming media</a> or in other situations where speed is an issue and some data loss may be tolerated because of the transitory nature of the data. </p><p>Often, a reliable unicast protocol is also <a href="/facts/Connection_oriented/2yAhgueh">connection oriented</a>. For example, TCP is connection oriented, with the <a href="/facts/Virtual_circuit/8HqpnTxl">virtual-circuit</a> ID consisting of source and destination <a href="/facts/IP_address/z9V22Sw9">IP addresses</a> and port numbers. However, some unreliable protocols are connection oriented, such as <a href="/facts/Asynchronous_Transfer_Mode/SzA8ewFL">Asynchronous Transfer Mode</a> and <a href="/facts/Frame_Relay/bFdv0qIP">Frame Relay</a>. In addition, some connectionless protocols, such as <a href="/facts/IEEE_802.11/ryEGu6Vq">IEEE 802.11</a>, are reliable. </p>