http://www.rfc-editor.org/rfc/rfc4497.txt
RFC 4497: Interworking between the Session Initiation Protocol (SIP) and QSIG, J. Elwell, F. Derks, P. Mourot, O. Rousseau2006-05-01T23:00:00-00:00This document specifies interworking between the Session Initiation Protocol (SIP) and QSIG within corporate telecommunication networks (also known as enterprise networks). SIP is an Internet application-layer control (signalling) protocol for creating, modifying, and terminating sessions with one or more participants. These sessions include, in particular, telephone calls. QSIG is a signalling protocol for creating, modifying, and terminating circuit-switched calls (in particular, telephone calls) within Private Integrated Services Networks (PISNs). QSIG is specified in a number of Ecma Standards and published also as ISO/IEC standards. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.