CCITT Ⅻ研究组研究电话传输性能与市话网。在1977～1980年研究期共有课题22个,收到文稿220篇。80年3月召开了本研究期的末期会议,有32个国家和科研工业组织的代表共78名参加了会议。 Ⅻ组从电话使用角度,研究一条电话连接,从话机特性到传输通路中各种损害因素所应符合的规定,以及用户的满意程度。因此Ⅻ组被称为传统的电话传输质量的保护者。 CCITT Ⅻ research group to study the telephone transmission performance and local network. During the study period from 1977 to 1980, there were 22 subjects and 220 articles were received. In March 1980, the final session of the study was held. A total of 78 representatives from 32 countries and research industrial organizations attended the meeting. Ⅻ Group from the phone point of view, study a telephone connection, from the phone features to the transmission path of various damage factors should meet the requirements, as well as user satisfaction. Therefore, the group called the traditional telephone transmission quality protector.