Version 2 of HTTP

HTTP/2 is an optimization of HTTP 1.1. Many browsers already support HTTP/2; your Chrome browser does that already.

HTTP/2 is a combination of two specifications: Hypertext Transfer Protocol version 2 (RFC7540) and HPACK- Header Compression for HTTP2 (RFC7541).

When using HTTP/2 over Transport Layer Security (TLS), "h2" is used to indicate the protocol.

The "h2c" string is used when HTTP/2 is used over clear text TCP or when HTTP.1.1 upgrades.

An example of a GET request is as follows:

-RCF 7540 Section 3.2

This request is from a client that does not know whether HTTP/2 is supported. It makes a HTTP 1.1 request, but includes an upgrade field in the header, "h2c", and at least one HTTP2-Settings header field:

-RCF 7540 Section 3.2

This looks like a regular HTTP/1.1 response:

-RCF 7540 Section 3.2

A frame is introduced as basis unit in HTTP2. You can think of a frame as a packet that is transferred over the wire. For requests and responses, the HEADER and DATA frames are used as the building blocks, and for HTTP/2 features, the frames are SETTINGS, WINDOWS_UPDATE, and PUSH_PROMISE.