TCP

TCP (Transmission Control Protocol) is one of the internet's foundational transport protocols. It sits between applications and the IP layer, converting an unreliable packet network into a dependable byte stream with delivery guarantees.

Core Features of TCP

• Reliable delivery: Missing segments are retransmitted until the receiver has complete, error-free data.
• Connection oriented: Sessions open with a three-way handshake and close with a four-step teardown.
• Flow control: A sliding window paces the sender so the receiver is never overwhelmed.
• Congestion control: Slow start and congestion avoidance adapt the rate to network conditions.
• Order preservation: Out-of-order packets are buffered and resequenced before delivery.

Where TCP Is Used

• Browsing: HTTP and HTTPS run on TCP.
• Mail: SMTP, IMAP and POP3 all use TCP.
• File transfers: FTP depends on TCP reliability.
• Remote access: SSH and Telnet are TCP applications.