摘要 |
A modem capable of transmitting data at a rate substantially greater than 28.8kb/s over a telephone network can be constructed by arranging for the modem output to be a series of analogue voltage levels which convert to a PCM data stream identical to the incoming data stream. A data transmission system using the present invention, includes a first modem and a second modem and a telephone network having a PCM telephone transmission link. Each modem includes: combining means adapted to combine an incoming data stream into bytes; and a digital to analogue convertor adapted to convert said bytes into a series of analogue voltage levels. The series of analogue voltage levels can be transmitted over an analogue transmission link to a PCM analogue to digital convertor, which may be located in a telephone exchange. The data transmission system is so arranged that a PCM output signal from said PCM analogue to digital convertor substantially replicates said incoming data stream. <IMAGE> |