Explain the working principle of the TCP protocol and how it ensures reliable data delivery.

TCP (Transmission Control Protocol) is a transport layer protocol that provides reliable, ordered, and error-free delivery of data between two nodes in a network.

Main mechanisms of TCP for reliability:

• Connection establishment (3-way handshake): the client and server exchange SYN and ACK messages to establish a connection.
• Segment numbering: each byte of data has a sequence number, allowing tracking of order and loss.
• Acknowledgments (ACK): the receiver sends acknowledgments upon receiving data.
• Retransmission: if acknowledgment is not received within a timeout, data is resent.
• Flow control: TCP uses a sliding window to regulate transmission speed to prevent overwhelming the receiver.
• Congestion control: adjusts transmission speed based on network conditions.

Example: when transmitting a file, TCP ensures that all parts of the file arrive in the correct order and without errors, retransmitting lost packets.