Information technology -- Telecommunications and information exchange between systems -- Corporate Telecommunication Networks -- Signalling interworking between QSIG and H.323 -- Call completion supplementary services

ISO/IEC 21991:2002 specifies signalling interworking between "QSIG" and "H.323" in support of call completion supplementary services within a Corporate telecommunication Network (CN).

"QSIG" is a signalling protocol that operates at the Q reference point between Private Integrated services Network eXchanges (PINX) within a Private Integrated Services Network (PISN). The Q reference point is defined in ISO/IEC 11579-1. A PISN provides circuit-switched basic services and supplementary services to its users. QSIG is specified in other Standards, in particular ISO/IEC 11572 (call control in support of basic services), ISO/IEC 11582 (generic functional protocol for the support of supplementary services) and a number of standards specifying individual supplementary services. ISO/IEC 13870 specifies the QSIG protocol in support of call completion services.

"H.323" is a set of signalling protocols for the support of voice or multimedia communication within a packet network, in particular a packet network that uses the Internet Protocol (IP) as its network layer protocol (IP network). H.323 signalling protocols operate between endpoints in an IP network, either indirectly via one or more