ETSI ETS 300 103-1990 综合业务数字网(ISDN).对ISDN同步和异步终端适配功能的基于CCITT 建议X.21,X.21(第二回)和X.20(第二回) 的数据终端设备(DTEs)的支持
Integrated Services Digital Network (ISDN); Support of CCITT Recommendation X.21, X.21 bis and X.20 bis Based Data Terminal Equipments (DTEs) by an ISDN Synchronous and Asynchronous Terminal Adaption Functions