Presence and instant messaging are defined in RFC 2778. The Common Profiles for Presence and Instant Messaging define two Universal Resource Identifier (URI) schemes: 'im' for INSTANT INBOXes and 'pres' for PRESENTITIES. This document provides guidance for locating the resources associated with URIs that employ these schemes.
RFC 3861-2004 history
2004RFC 3861-2004 Address Resolution for Instant Messaging and Presence