Transmission Control Protocol
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J. Postel · 1981-09
Abstract
RFC 793 specifies the Transmission Control Protocol (TCP), a connection-oriented, reliable, byte-stream transport protocol. TCP provides flow control, error detection and retransmission, sequencing, and congestion avoidance for applications exchanging data over IP networks.
Why This RFC Matters
TCP, as defined in RFC 793, is arguably the most important protocol specification ever written. By providing reliable, ordered delivery over an unreliable network, TCP made it practical to build applications — email, file transfer, the World Wide Web — without worrying about the underlying network's imperfections. The three-way handshake, sliding window flow control, and sequence-number-based retransmission described in RFC 793 remained essentially unchanged for decades. The protocol was eventually consolidated and clarified in RFC 9293 in 2022, but the core mechanisms Jon Postel designed in 1981 are still running the internet today.