stuff i learn

quick UDP internet connections (QUIC)

2 min read

why is QUIC quick?

a Layer 4 protocol that uses another Layer 4 protocol (UDP) as its foundation to create a new, more powerful transport service

  • the transport layer protocol of choice for HTTP/3

QUIC uses UDP (port 443), so the widespread adoption of HTTP/3 (and by association QUIC) requires companies worldwide to stop blocking UDP

  • UDP is often blocked by firewalls and networks for security and performance reasons, including its lack of reliability, congestion control, and built-in authentication

a key difference between QUIC and UDP is that QUIC features congestion control

  • QUIC’s congestion control runs in user-space, not in the OS kernel like traditional TCP
  • allows updates to the congestion control algorithms without needing an OS update

”solving” HOL blocking (and some history)

HTTP/2 introduces a binary framing layer between the high-level HTTP semantics (like verbs and headers) and the underlying TCP connection

  • each request-response pair is assigned to its own independent stream - a single TCP connection can have multiple streams open simultaneously
  • each stream is broken down into smaller chunks of data called frames, and tagged with the ID of the stream it belongs to
  • HTTP/2 interleaves frames from different streams (multiplexing) over the single TCP connection, and the receiving end then reassembles the frames into their respective streams
    • in doing so, we don’t have to wait for ITEM1 to be received before receiving ITEM2
      QUIC takes the stream multiplexing from HTTP/2 and moves it from the application layer down to the transport layer
  • ie. QUIC packet containing data from StreamA, StreamB, StreamC is dropped → StreamD is not blocked

does it really help?

unfortunately, most of the latency (usually) incurred is due to the handshake from HTTPS, not HOL blocking - performance gains (from this) is usually minimal

  • unless you drop a lot of packages!

there are other benefits of QUIC that is not mentioned here (eg. built in TLS1.3)

Networking UDP QUIC

Graph View