Compare TCP and UDP. Give one application that suits each and explain why.
Show the explanation
Model answer. TCP is connection-oriented (three-way handshake), reliable (acknowledgements, retransmission), ordered, and has flow and congestion control; it presents a byte stream. UDP is connectionless and sends independent datagrams with no delivery or ordering guarantee and very little overhead.
- TCP: web pages, file transfer, email — every byte must arrive correctly and in order.
- UDP: live voice/video, online games, DNS queries — a late packet is useless, so retransmitting it only adds delay; the application handles loss itself.
Mention that QUIC (used by HTTP/3) builds reliability on top of UDP, which shows the trade-off is about where reliability is implemented.
Original UniCircle question. Last reviewed 21 Oct 2026.