> For the complete documentation index, see [llms.txt](https://http3-explained.haxx.se/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://http3-explained.haxx.se/en/the-protocol/feature-reliable.md).

# Reliable

While UDP is not a reliable transport, QUIC adds a layer on top of UDP that introduces reliability. It offers re-transmissions of packets, congestion control, pacing and the other features otherwise present in TCP.

Data sent over QUIC from one end-point will appear in the other end sooner or later, as long as the connection is maintained.