A New Transport Underneath
HTTP version three keeps the ideas of streams and multiplexing but runs over QUIC instead of TCP. QUIC is built on UDP and folds in encryption and stream awareness at the transport layer.
Independent Streams in Transport
In HTTP version two, streams share one ordered TCP byte stream, so a single lost packet stalls every stream. QUIC gives each stream its own ordering, so loss on one stream does not block the others.
- Each QUIC stream is delivered and ordered independently.
- A lost packet only delays the streams whose data it carried.
- This removes head of line blocking at the transport layer, not just the HTTP layer.
Faster Connection Setup
QUIC merges the transport and cryptographic handshakes, so a connection can be established in fewer round trips than TCP plus a separate security handshake. Resumed connections can even send data immediately.
Connection Migration
Because QUIC identifies a connection by an id rather than the address pair, a client can change networks, such as moving from a wireless network to a mobile one, without dropping the connection.
Key idea
HTTP version three runs over QUIC on UDP, giving each stream independent ordering to remove transport level head of line blocking, while merging handshakes for faster setup and supporting connection migration across networks.