Understanding TCP and UDP: Principles, Differences, and Communication Processes

TCP and UDP are transport‑layer protocols used for transmitting various types of data (files, video, images) between applications.

Role : Both operate at the transport layer; TCP offers reliable, connection‑oriented communication, while UDP provides fast, connectionless transmission.

Differences : TCP establishes a connection, ensures ordered delivery and error checking, making it suitable for file transfer, email, and web browsing; UDP does not maintain a connection, offering lower latency for DNS queries, voice calls, video streaming, and tunneling (e.g., VXLAN), but may lose packets.

TCP Three‑Way Handshake : The client initiates a connection with a SYN packet, the server replies with SYN‑ACK, and the client completes the handshake with ACK, preventing issues caused by stale SYN packets in unreliable networks.

TCP Four‑Way Termination : Connection closure requires four steps—FIN from the client, ACK from the server, FIN from the server, and final ACK from the client—plus a timeout to guarantee both sides have received the final acknowledgment.

Data Transmission in TCP : TCP assigns sequence numbers to each byte, uses acknowledgments (ACK) to confirm receipt, and employs retransmission and flow control to handle packet loss, reordering, and congestion.

Data Transmission in UDP : UDP simply encapsulates data into packets and sends them without maintaining state, resulting in minimal overhead but no delivery guarantees.