QSIG is an ISDN based signaling protocol for signaling between private branch exchanges (PBXs) in a private integrated services network (PISN). It makes use of the connection-level Q.931 protocol and the application-level ROSE protocol. ISDN "proper" functions as the physical link layer. QSIG was originally developed by Ecma International, adopted by ETSI and is defined by a set of ISO standard documents, so is not owned by any company. This allows interoperability between communications platforms provided by disparate vendors. QSIG has two layers, called BC (basic call) and GF (generic function). QSIG BC describes how to set up calls between PBXs. QSIG GF provides supplementary services for large-scale corporate, educational, and government networks, such as line identification, call intrusion and call forwarding. Thus for a large or very distributed company that requires multiple PBXs, users can receive the same services across the network and be unaware of the switch that their telephone is connected to. This greatly eases the problems of management of large networks. QSIG will likely never rival each vendor's private network protocols, but it does provide an option for a higher level of integration than that of the traditional choices. List of QSIG standards Note: This list is not complete. See the "source" after the list for more information. ECMA-143 - Private Integrated Services Network (PISN) - Circuit Mode Bearer Services - Inter-Exchange Signalling Procedures and Protocol (QSIG-BC), Basic Call, International and European Versions: ISO/IEC 11572, ETSI EN 300 172 ECMA-165 - Private Integrated Services Network (PISN) - Generic Functional Protocol for the Support of Supplementary Services - Inter-Exchange Signalling Procedures and Protocol (QSIG-GF), International and European Versions: ISO/IEC 11582, ETSI ETS 300 239 ECMA-164 - Private Integrated Services Network (PISN) - Inter-Exchange Signalling Protocol - Name Identification Supplementary Services (QSIG-NA), International and European Versions: ISO/IEC 13868, ETSI ETS 300 238 ECMA-174 - Private Integrated Services Network (PISN) - Inter-Exchange Signalling Protocol - Call Diversion Supplementary Services (QSIG-CF), International and European Versions: ISO/IEC 13873, ETSI ETS 300 257 ECMA-178 - Private Integrated Services Network (PISN) - Inter-Exchange Signalling Protocol - Call Transfer Supplementary Service (QSIG-CT), International and European Versions: ISO/IEC 13869, ETSI ETS 300 261 Source : ECMA - list of standards (search the list for PISN to find all QSIG related standards at ECMA) QSIG basically uses ROSE to invoke specific supplementary service at the remote PINX. These ROSE operations are coded in a Q.931 FACILITY