DIN ETS 300204-1995 综合服务数字网络.转呼无条件的补充业务.功能效率和信息流通; 英文版本 ETS 300204:1994
Integrated Services Digital Network (ISDN) - Call Forwarding Unconditional (CFU) supplementary service - Functional capabilities and information flows; English version ETS 300204:1994