ETSI PRTBR 17-1995 商务通信(BTC).普通质量和高质量声音带宽4线模拟租用线(A4O 和A4S)的终端设备接口附加要求
Business TeleCommunications (BTC); Ordinary and Special Quality Voice Bandwidth 4-Wire Analogue Leased Lines (A4O and A4S); Attachment Requirements for Terminal Equipment Interface