RFC 675 first specified the Transmission Control Program in December 1974.
Titled “Specification of Internet Transmission Control Program,” RFC 675 described a protocol for communication across interconnected packet-switched networks. It defined functions for process-to-process communication, including connections, ports, sequencing, acknowledgments, retransmission, and flow-control mechanisms. The document treated the network as a collection of different packet systems that needed a common end-to-end protocol.
Vinton Cerf, Yogen Dalal, and Carl Sunshine authored RFC 675. Their work grew from the problem of linking unlike networks such as the ARPANET, packet-radio networks, and satellite networks. The original Transmission Control Program was a broad, monolithic design. During later development, its functions were separated into TCP and IP, the architecture that became central to the modern Internet.
RFC 675 is historic rather than the final TCP specification. It was eventually superseded by later documents, including RFC 793, which defined the standardized Transmission Control Protocol. RFC 821 specified SMTP, RFC 791 specified IP, and RFC 1 was the first Request for Comments—not the first TCP specification.