QUIC / HTTP/3

HTTP/2 multiplexes requests, but all streams still share one TCP connection. Packet loss at TCP can temporarily affect progress across that connection. Connection establishment also has latency costs.

QUIC implements secure multiplexed transport over UDP. One QUIC connection between browser and server carries multiple streams—for example, separate HTML, CSS, and image requests and responses, each identified by a stream ID. UDP datagrams can arrive out of order or be lost. QUIC adds numbered packets, acknowledgements, and retransmission of lost stream data in new packets. Stream IDs and byte offsets let the receiver reconstruct each stream in order. HTTP/3 uses these reliable streams for requests and responses. If image data is lost, that stream waits for recovery while an unaffected API stream can continue; ordering is maintained within each stream.

HTTP/3
  ↓
QUIC
  ↓
UDP
  ↓
IP

Streams can recover more independently.