Transmission of digital information over telephone circuits

The problems of transmission of digital data over commercial telephone lines are studied with particular attention to transmitting telephone numbers over a wide variety of circuits. The electrical characteristics of these lines and the noise present on them are major factors which influence the design of a reliable high-speed data transmission system. A system which takes account of these factors has been designed and tested. The results of tests indicate that it operates reliably on almost all message circuits at a rate of about 650 bits per second with signals occupying the band from 700 to 1,700 cycles.