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Transmission Control Protocol
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<p>The Transmission Control Protocol (TCP) is one of the main <a href="/facts/Communications_protocol/5uady7cB">protocols</a> of the <a href="/facts/Internet_protocol_suite/KNkxtSpw">Internet protocol suite</a>. It originated in the initial network implementation in which it complemented the <a href="/facts/Internet_Protocol/Qq6VeEal">Internet Protocol</a> (IP). Therefore, the entire suite is commonly referred to as <a href="/facts/TCP%2fIP/KNkxtSpw">TCP/IP</a>. TCP provides <a href="/facts/Reliability_(computer_networking)/v3kGvfvs">reliable</a>, ordered, and <a href="/facts/Error_detection_and_correction/o2rH8e3n">error-checked</a> delivery of a <a href="/facts/Reliable_byte_stream/YbSblvM5">stream</a> of <a href="/facts/Octet_(computing)/dqCHsuUF">octets</a> (bytes) between applications running on hosts communicating via an IP network. Major internet applications such as the <a href="/facts/World_Wide_Web/wvnTrWFq">World Wide Web</a>, email, <a href="/facts/Remote_administration/sPIwCm1S">remote administration</a>, and <a href="/facts/File_transfer/9qP8HDW8">file transfer</a> rely on TCP, which is part of the <a href="/facts/Transport_layer/UmIGUCeK">transport layer</a> of the TCP/IP suite. <a href="/facts/Transport_Layer_Security/pGy16TnA">SSL/TLS</a> often runs on top of TCP. </p><p>TCP is <a href="/facts/Connection-oriented_communication/2yAhgueh">connection-oriented</a>, meaning that sender and receiver firstly need to establish a connection based on agreed parameters; they do this through three-way handshake procedure. The server must be listening (passive open) for connection requests from clients before a connection is established. Three-way <a href="/facts/Handshake_(computing)/fqKIh1VW">handshake</a> (active open), <a href="/facts/Retransmission_(data_networks)/Em3pHg0f">retransmission</a>, and error detection adds to reliability but lengthens <a href="/facts/Network_latency/6Bjhn30H">latency</a>. Applications that do not require reliable <a href="/facts/Data_stream/57yDhBCd">data stream</a> service may use the <a href="/facts/User_Datagram_Protocol/dxLU0D6q">User Datagram Protocol</a> (UDP) instead, which provides a <a href="/facts/Connectionless_communication/MfMys8t7">connectionless</a> <a href="/facts/Datagram/TMHVctMz">datagram</a> service that prioritizes time over reliability. TCP employs <a href="/facts/TCP_congestion_control/gC9Fer09">network congestion avoidance</a>. However, there are vulnerabilities in TCP, including <a href="/facts/Denial-of-service_attack/6nkoK02J">denial of service</a>, <a href="/facts/TCP_sequence_prediction_attack/ztRnjlv2">connection hijacking</a>, TCP veto, and <a href="/facts/TCP_reset_attack/jULWJHnY">reset attack</a>. </p>