DIN EN 301048:1998
专用综合业务网(PISN).内部交换信令协议..转接计数器附加网络特性
Private Integrated Services Network (PISN) - Inter-exchange signalling protocol - Transit counter additional network feature [ISO/IEC 15055 (1997) modified]; English version EN 301048 V 1.1.1 (1997.09)