Reliable delivery or timely arrival?
TCP and UDP provide different transport building blocks. Applications decide how to use them.
In 30 seconds
- TCP supplies an ordered byte stream with retransmission when needed.
- UDP does not itself guarantee delivery or ordering.
- An application can add reliability above UDP, as QUIC does.
Make it concrete
A file needs its missing bytes. In a live call, an old syllable arriving late may be less useful than the next syllable on time.
- 01Application
- 02Transport
- 03IP network
Check your understanding
Does using UDP mean an application can never provide reliable delivery?
- TCP supplies an ordered byte stream with retransmission when needed.
- UDP does not itself guarantee delivery or ordering.
- An application can add reliability above UDP, as QUIC does.
Go to the source
Sources reviewed: 13.09.2026