"Foreword This European Standard (Telecommunications series) has been produced by ETSI Technical Committee European Computer Manufacturers Association (ECMA). The present document is one of a series of standards defining services and signalling protocols applicable to Private Integrated Services Networks (PISN). The series uses the Integrated Services Digital Network (ISDN) concepts as developed by ITU-T and conforms to the framework of standards for Open Systems Interconnection (OSI) as defined by ISO/IEC. This particular EN specifies the Q interface Signalling protocol (QSIG) protocol for use at the Q reference point in support of the Advice of Charge Supplementary Services. The QSIG protocol is known as ""Private integrated Signalling System no. 1"" (PSS1) in International Standards."