XMPP Real-Time Messaging Protocol

XMPP (Extensible Messaging and Presence Protocol) is an open XML-based communication protocol for near-real-time messaging, presence information, and contact list maintenance. Originally developed as Jabber by Jeremie Miller in 1999, XMPP was formalized as IETF RFC 6120 and RFC 6121 standards and has been used by Google Talk, WhatsApp (internal), Facebook Chat, and millions of federated IM services worldwide. Key features include: decentralized federation (server-to-server communication enabling users on different domains to communicate, similar to email, preventing vendor lock-in and centralization), XML streaming (lightweight XML stanza-based protocol over TCP with TLS encryption, port 5222 for client-server and port 5269 for server-to-server), presence (real-time online status notification across contacts and groups), contact list (roster management for subscribing to and managing presence subscriptions), publish-subscribe (XEP-0060 for event notifications, news feeds, and microblogging), multi-user chat (XEP-0045 for group chat rooms with roles, moderation, and history), file transfer (XEP-0096, SOCKS5 Bytestreams, and HTTP Upload for large file sharing), voice and video (Jingle XEP-0166 for WebRTC-compatible real-time multimedia sessions), data forms (XEP-0004 for structured form-based interaction), service discovery (XEP-0030 for discovering server capabilities and services), security (SASL authentication, TLS encryption, and certificate-based trust), and extensibility (XEP specification process with over 400 extensions covering IoT, gaming, social networking, and enterprise communication).