Instant Messaging (IM)
Client-Server model
XMPP / Jabber protocol
XMPP / Jabber server

Concepts bullet XMPP / Jabber protocol

What is XMPP? What is jabber?

Extensible Messaging and Presence Protocol (XMPP) is an open-standard communications protocol for message-oriented middleware based on Extensible Markup Language (XML). Early on, this protocol was called jabber and it was meant for near-real-time, extensible instant messaging (IM), presence information, and contact list maintenance. Designed to be extensible, the protocol today also finds application in Voice over Internet Protocol and file transfer signaling.