http://www.rfc-editor.org/rfc/rfc2976.txt
RFC 2976: The SIP INFO Method, S. Donovan2000-10-01T23:00:00-00:00This document proposes an extension to the Session Initiation Protocol (SIP). This extension adds the INFO method to the SIP protocol. The intent of the INFO method is to allow for the carrying of session related control information that is generated during a session. [STANDARDS-TRACK]