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Networking Fundamentals · Foundational

Transmission Control Protocol (TCP)

A connection-oriented Layer 4 protocol that provides reliable, ordered, error-checked delivery of a byte stream.

Definition

TCP (RFC 9293) establishes connections with a three-way handshake, numbers each byte with sequence numbers, acknowledges received data, retransmits lost segments, and uses windowing for flow control and congestion control. Its header is 20 to 60 bytes. Applications using TCP include HTTP/HTTPS, SSH, SMTP, FTP, IMAP and RDP.

Example

An SSH session to port 22 runs over TCP.

Exam tip

Pick TCP when the scenario stresses reliability or guaranteed delivery; pick UDP for speed, streaming, voice or simple queries.

Don't confuse it with

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