TCP

TCP is the transport protocol that powers the majority of internet applications. It sits above IP and creates virtual connections that survive packet loss and reordering, so applications can simply read and write data as a continuous stream.

TCP's Reliability Toolkit

• Acknowledgements: The receiver confirms each segment; unacknowledged ones are resent.
• Session lifecycle: Communication begins with a three-way handshake and ends with a four-way close.
• Sliding window: The sender's rate is matched to what the receiver can accept.
• Congestion adaptation: Algorithms like slow start keep the network from being flooded.
• Byte ordering: Data is reassembled in the correct order at the destination.

Typical Uses of TCP

• Web: HTTP/HTTPS traffic travels over TCP.
• Email: SMTP, IMAP, POP3 are TCP-based.
• File sharing: FTP relies on TCP's reliable transport.
• System admin: SSH and Telnet run over TCP.