ETSI ETS 300 210-1-1996 综合业务数字网(ISDN).免费电话(FPH)补充业务.1号数字用户信令系统(DSS1)协议.第1部分:协议规范
Integrated Services Digital Network (ISDN); Freephone (FPH) Supplementary Service; Digital Subscriber Signalling System No. One (DSS1) Protocol; Part 1: Protocol Specification