XMPP: The Definitive Guide

Chapter 2. Basics of XMPP

This chapter outlines the fundamental features used by all XMPP-based applications. We first describe the generic architecture of XMPP systems and then the addressing scheme for XMPP communications, the three communication “primitives,” the model for sharing information about availability on the network (called presence), and the processes for session establishment.

Architecture

All good Internet technologies have an “architecture”—a way that various entities fit together, link up, and communicate. For example, the World Wide Web consists of millions of web servers running software like Apache, and many more millions of web clients (browsers) running software like Firefox, all using standard protocols and data formats like HTTP and HTML. As another example, the email infrastructure consists of millions of email servers running software like Postfix, and many more millions of email clients running software like Thunderbird, all using standard protocols like SMTP, POP, and IMAP.

Similarly, the Internet’s infrastructure for instant messaging, presence, and other forms of real-time communication increasingly consists of hundreds of thousands of Jabber servers running software like ejabberd and Openfire, and millions of Jabber clients running software like Adium, Gajim, Pidgin, and Psi, all using the standard protocol we call XMPP.

XMPP technologies use a decentralized client-server architecture similar to the architectures used for the World Wide Web and the email ...