传真通信的国家标准。相当于ITU T.4， 文件传真三类机在电话网中的互通技术条件　第1部分：用于文件传输的三类传真终端的标准化-fax communications of the national standard. Elections equivalent to the ITU, the paper fax machine three telephone network in the exchange of technical conditions Part 1 : for the three types of file transfer fax terminals Standardization