http2

HTTP/2 is a major revision of the HTTP network protocol designed to improve performance by enabling multiple simultaneous exchanges over a single TCP connection. Derived from SPDY, it was standardized by the IETF in RFC 7540 in 2015 (with header compression defined in RFC 7541). The protocol introduces a binary framing layer and a multiplexing mechanism that lets many requests and responses share one connection without interfering with each other, reducing latency compared with HTTP/1.1.

Key features include binary framing, header compression using HPACK, server push, and flow control with per-connection and per-stream windows. Communications are conducted over streams identified by a stream ID. The protocol uses a SETTINGS frame to negotiate parameters, supports prioritization, and defines frame types such as HEADERS, DATA, PRIORITY, RST_STREAM, and WINDOW_UPDATE. HTTP/2 preserves HTTP semantics, including methods, status codes, and header fields, but moves to a binary format and compresses headers to reduce overhead.

Transport and deployment: HTTP/2 is typically negotiated over TLS using ALPN to select the protocol. It can also operate over cleartext using the h2c variant, but this is less common in production due to proxy configurations. Server push is optional and can be disabled on both client and server; it aims to proactively deliver resources the client will need, but it can complicate caching strategies.

Impact and adoption: HTTP/2 has broad support in major browsers and web servers and has become the standard baseline for modern web traffic. While it mitigates many performance issues of HTTP/1.1, it does not eliminate TCP-level head-of-line blocking entirely; HTTP/3, which uses QUIC over UDP, addresses that limitation more directly. HTTP/2 remains widely deployed and compatible with the existing web ecosystem.