This section provides a brief overview of the architecture of the Extensible Messaging and Presence Protocol (XMPP).
Introduction
The Extensible Messaging and Presence Protocol (XMPP) is an open XML-based protocol for near-real-time messaging, presence, and request-response services.
The protocol was originally named Jabber, and was developed by the Jabber open-source community in 1999 for near real-time, instant messaging (IM), presence information, and contact list maintenance. Designed to be extensible, the protocol has also been used for publish-subscribe systems, signalling for VoIP, video, file transfer, gaming, Internet of Things applications such as the smart grid, and social networking services.
Architecture
The XMPP network uses a client–server architecture (clients do not talk directly to one another). However, it is decentralized—by design, there is no central authoritative server, as there is with services such as AOL Instant Messenger or Windows Live Messenger.
Clients send and receive messages only to and from their respective server and it is the server's responsibility to route appropriately-addressed messages through the network to the intended user. For this purpose, every user on the network has a unique Jabber ID (usually abbreviated as JID ). To avoid requiring a central server to maintain a list of IDs, the JID is structured like an email address with a username and a domain name for the server where that user resides, separated by an at sign (@), such as username@example.com.
The following diagram provides a general overview of the XMPP architecture:
