What QUIC is
QUIC is a transport protocol built on top of UDP rather than TCP. It powers HTTP3, the newest version of HTTP. By living in user space, QUIC can evolve faster than TCP, which is baked into operating system kernels.
Why it matters
- Faster setup combines the transport and TLS handshakes, so a fresh connection often opens in one round trip, and zero with a resumed session.
- Independent streams mean a lost packet only stalls its own stream, not every other request sharing the connection.
- Connection migration lets a session survive a network change, such as moving from wifi to cellular, because connections are identified by an ID rather than the address pair.
How it relates to HTTP2
HTTP2 multiplexes streams over a single TCP connection, but a single lost packet stalls all of them because TCP enforces in order delivery. QUIC moves multiplexing below the application and gives each stream its own ordering, eliminating transport level head of line blocking. Encryption is mandatory and integrated, so even the transport metadata is protected.
Key idea
QUIC runs over UDP to fold in encryption, speed up handshakes, and give each stream independent delivery.