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The Internet: The TCP protocol

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TCP means Transfer Control Protocol, and it’s the basis of the Web and other applications like Email. Defined in RFC 793 in 1981, TCP is one of the oldest pillars of the Internet. TCP sits on top of the Internet Protocol (IP). Upon it, other application-level protocols like HTTP, FTP, IMAP (and many others) operate. TCP, contrary to IP and UDP, is connection oriented. Before transmission can happen over TCP, a connection must be established. Data is sent, in form of little packets, and when the communication ends the connection is closed. When data is transmitted over TCP, there’s a relatively complex workflow called handshake that must happen. I will not go into the details here, but this handshake allows the end-to-end connection to happen, and this makes sure TCP can provide one of its peculiar features: reliability. Using TCP, we can always know if a packet the sender sent was received correctly by the receiver. If a packet gets lost, the protocol is able to handle it and the packe

By Flavio Copes Mar 16, 2020updated Aug 11, 2026 Learn how TCP works by building a small Node.js server and client, sending data between them, and watching the connection from your terminal. ~~~ Every time you open a website, a small conversation starts between your computer and a server. Your browser sends a request. The server sends back HTML, CSS, images, and other data. TCP is often the protocol carrying that conversation. Many application protocols are built on top of it. HTTP/1.1 and HTTP/2 use TCP for the web. SSH uses it for remote shells. SMTP and IMAP use it for email. FTP…

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