TCP

TCP (Transmission Control Protocol) lives at the transport layer, adding structure to raw internet packets. It manages connections, numbers segments, and recovers from loss, turning the best-effort network into a channel applications can trust.

How TCP Guarantees Delivery

• Retransmission: Anything not acknowledged in time is sent again automatically.
• Stateful sessions: A three-way handshake opens connections; a four-way sequence closes them.
• Pacing: Flow control prevents senders from outrunning receivers.
• Congestion avoidance: Transmission rates react to observed network load.
• Sequencing: Data is handed to the application in the exact order sent.

Everyday TCP Applications

• Browsing: HTTP/HTTPS build on TCP.
• Email: SMTP, IMAP and POP3 depend on TCP.
• File transfer: FTP needs TCP's guarantees.
• Remote login: SSH and Telnet use TCP.