This Profile Standard specifies the combination of base standards@ together with the selection of appropriate options and parameter values@ necessary to specify how QSIG/PSS1 can be used to provide digital signalling capabilities between Private Integrated services Networks eXchange (PINX) in an Air Traffic Services (ATS) PISN. The present document defines: - physical and electrical characteristics (physical layer) of the interfaces to the transmission systems to be employed; - data link layer procedures to ensure error-free communications links; - network layer procedures for call establishment and clearing; and - supplementary services to meet specific ATS requirements. The present document states requirements upon implementations in order to achieve interoperability between equipment in ATS PISNs. NOTE 1: Implementation of the present document does not preclude a manufacturer from offering other means of interconnection. The present document does not specify requirements related to interworking between QSIG and other signalling systems used in ATS PISNs