Cianplan

Level 0: Orientation & prerequisites · L0.3 Networking: TCP/IP, TLS, HTTP/2/3, QUIC

HTTP/1.1 to HTTP/2 to HTTP/3

Explain multiplexing, head-of-line blocking and why QUIC runs on UDP.

13 min · Free

What you take away

  • HTTP/1.1 sends one request at a time per connection, so browsers open ~6 per origin and still queue.
  • HTTP/2 multiplexes many streams over one connection, removing HTTP-level queueing and repeated headers.
  • Those streams still share one TCP connection, so a single lost packet stalls all of them — TCP head-of-line blocking.
  • HTTP/3 runs on QUIC over UDP: loss recovery is per stream, the handshake is folded into TLS 1.3, and connections survive a network change.

How the class is laid out

  1. The problem
  2. The simple version
  3. What each version fixed
  4. Check your understanding