HTTP/2 Protocol Specification

HTTP/2 is the second major version of the Hypertext Transfer Protocol, standardized as RFC 7540 (later updated by RFC 9113 in 2022) by the IETF HTTP Working Group. Published in May 2015, HTTP/2 was developed based on Google SPDY protocol and is now supported by all major web servers and browsers. Key improvements over HTTP/1.1: multiplexing (multiple concurrent requests and responses over a single TCP connection, eliminating head-of-line blocking and reducing connection overhead). Binary framing (binary protocol with fixed-length frame headers instead of text-based parsing, enabling more efficient parsing and smaller overhead). Header compression (HPACK header compression algorithm reducing redundant header data by maintaining static and dynamic header tables, significantly reducing bandwidth). Server push (server can proactively push resources to client before they are requested, though this feature has been deprecated in practice due to implementation complexity and cache inefficiency). Stream prioritization (client can assign priority weights and dependencies to streams, enabling more intelligent resource allocation). Single connection (one TCP connection per origin reduces TLS handshake overhead and connection setup time). Flow control (per-stream and per-connection flow control via WINDOW_UPDATE frames for backpressure management). Transition from HTTP/1.1 (servers negotiate HTTP/2 via ALPN TLS extension or Upgrade header for plaintext). Performance benefits include reduced latency, improved page load times, and better connection utilization. Widely deployed with over 50 percent of all websites using HTTP/2 as of 2026. Supported by nginx, Apache httpd, Cloudflare, and all major CDNs.