Service integrated digital transmission system

Claim 1

In a service integrated transmission system, including a first terminal containing a transmitter, a second terminal containing a receiver, and a transmission path connecting the terminals together, for transmitting, over the transmission path, digital signals having a transmission band whose upper limit frequency corresponds to the maximum bit rate of the signals to be transmitted, the transmission being effected by simultaneously transmitting, over the transmission path, digital signals having a high bit rate only in an upper part of the transmission band and digital signals having a low bit rate only in a lower part of the transmission band, the improvement wherein: said transmission path is a light signal transmission path; said transmitter comprises first signal supply means for supplying a plurality of individual signals having a low bit rate as narrowband signals, second signal supply means for supplying a plurality of individual signals having a high bit rate as broadband signals, first multiplexing means connected to said first signal supply means for combining the plurality of low bit rate signals into a narrowband multiplex signal, second multiplexing means connected to said second signal supply means for combining the plurality of high bit rate signals into a broadband multiplex signal, adding means connected to said first and second multiplexing means for additively combining the narrowband and broadband multiplex signals into a combined multiplex signal having an associated frequency band in which the broadband multiplex signal occupies an upper part of the frequency band and the narrowband multiplex signal occupies a lower part of the frequency band, and light signal generating means connected between said adding means and said light signal transmission path for converting the combined multiplex signal into a light signal and conducting the light signal to said light transmission path; and said receiver comprises light signal receiving means optically coupled to said light transmission path for converting the light signal transmitted over that path into an electrical signal, corresponding to the broadband signal formed by said adding means, signal separating means connected to said receiving means for separating the electrical signal into a low frequency component containing the narrowband multiplex signal and a high frequency component containing the broadband multiplex signal, and demultiplexing means connected to said signal separating means for separating each of the broadband and narrowband signals into a respective individual signal corresponding to those supplied by said signal supply means.