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RFC 9113 / START HERE

HTTP/2, before the details

HTTP/2

HTTP means Hypertext Transfer Protocol. HTTP/2 carries multiple request and response streams over one TCP connection using binary frames.

Start the guide See the 5 chapters ↓

The idea in one picture

  1. A browser makes several requests

  2. HTTP/2 shares a TCP connection

  3. Responses use separate streams

A simplified picture of the idea; the chapters explain the actual mechanisms.

Why it exists

A web page can need many resources. Sharing one connection helps avoid treating every exchange as a separate connection.

A familiar example

A browser requests a page, styles, and images on separate HTTP/2 streams within one connection.

Helpful background

You can start here without reading another RFC. If these ideas are unfamiliar, these short introductions may help.

HTTPRFC 9110 · beginner overview ↗TCPRFC 9293 · beginner overview ↗

What you’ll learn next

Begin with chapter one, or choose a topic.

  1. Connection prefaceBoth peers establish HTTP/2 state before exchanging ordinary requests.
  2. Multiplexed streamsFrames for several exchanges share a connection, with stream identifiers keeping their state separate.
  3. Frames and compressed fieldsA nine-octet frame header identifies length, type, flags, and stream.
  4. Receiver flow-control creditDATA must fit both the stream window and the connection window.
  5. Reset and graceful shutdownA broken stream and a broken connection require different signals.
Start with chapter one →
EXPLORE THIS PROTOCOL

HTTP versions

HTTP semantics apply across versions. HTTP/2 and HTTP/3 change how messages travel; all three guides remain relevant.

RFC 9110HTTP semanticsShared methods, status codes, and message meaningRFC 9113 · YOU ARE HEREHTTP/2Multiplexed streams over TCPRFC 9114HTTP/3HTTP over QUIC

This introduction explains RFC 9113 (2022). Read the original RFC ↗