ETSI PRTBR 21-1997 将TE连接到模拟公共交换电话网(PSTNs)的泛欧批准的附加要求(不包括支持语音电话业务的TE),其中网络寻址(若有)是通过双音多频信令来实现的
Attachment Requirements for Pan-European Approval for Connection to the Analogue Public Switched Telephone Networks (PSTNs) of TE (Excluding TE Supporting the Voice Telephony Service) in Which Network Addressing, if Provided, is by Means of Dual Tone Mult