The Transmission Control Protocol (TCP) is a core protocol of the Internet Protocol (IP) suite, operating at the Transport Layer (Layer 4) of the OSI model. Its primary function is to ensure the reliable, ordered, and error-checked delivery of data streams between applications.
To achieve this reliability, TCP is a "connection-oriented" protocol. Before data transfer begins, applications establish a connection via a process known as a "three-way handshake." Once connected, TCP segments data into packets, assigns sequence numbers, and transmits them. The receiving end reassembles these packets in the correct order and verifies them for errors. If packets are lost or corrupted, TCP automatically requests retransmission.
This process guarantees that data arrives complete and in the correct sequence. Consequently, TCP is the standard choice for applications where data integrity is critical, such as web browsing (HTTP), file transfers (FTP), and the remote control of programmable instruments over LAN. While TCP introduces slightly higher latency and overhead compared to the connectionless UDP protocol, its reliability makes it essential for accurate industrial control.
Note: The TCP specification is currently defined in RFC 9293, which consolidated and superseded the original RFC 793.