http://www.rfc-editor.org/rfc/rfc6502.txt
RFC 6502: Conference Event Package Data Format Extension for Centralized Conferencing (XCON), G. Camarillo, S. Srinivasan, R. Even, J. Urpalainen2012-03-01T23:00:00-00:00This document specifies the notification mechanism for XCON (centralized conferencing). This mechanism reuses the SIP (Session Initiation Protocol) event package for conference state. Additionally, the notification mechanism includes support for the XCON data model and for partial notifications. [STANDARDS-TRACK]