TCP vs. UDP: Choosing the Right Transport

TCP gives an application a reliable, ordered byte stream. It establishes a connection, detects loss, retransmits data, and provides flow and congestion control. The receiver sees bytes in order, but not the sender's write boundaries, so the application protocol must frame its own messages.

UDP sends independent datagrams without establishing a transport connection. A datagram may be lost, duplicated, or arrive out of order. UDP does not hold a later datagram until an earlier one arrives, and it preserves datagram boundaries. If the application needs reliability or ordering, it must add those features above UDP. Internet applications using UDP also need suitable congestion control.

Choose based on the application's failure and latency requirements, not a blanket speed ranking. TCP suits file transfers, database connections, and other cases that need an ordered, reliable stream. UDP suits latency-sensitive updates where stale data is less useful than fresh data, or protocols that implement their own transport behavior. Voice and game updates are common examples. UDP has less built-in machinery, but it is not automatically faster. Recreating reliable, ordered delivery over UDP also recreates much of TCP's work.