ETSI EN 300 356-9-2001 综合业务数字网(ISDN).7号信令系统(SS7).国际接口的ISDN用户部分(ISUP)版本4.第9部分:闭合用户群(CUG)补充业务(版本4.1.2).ITU-T建议Q.73735,第1条(1993),修正本
Integrated Services Digital Network (ISDN); Signalling System No.7 (SS7); ISDN User Part (ISUP) Version 4 for the International Interface; Part 9: Closed User Group (CUG) Supplementary Service (V4.1.2; ITU-T Recommendation Q.735, Clause 1 (1993) Modified)