transmission line into more segments wherein an isolated segment is formed between adjacent scu pairs or between the scu and the ends or terminators of transmission lines the function of the scu has been so far been described only as a terminator but an scu can also be modified to perform a line receiving function as shown in fig9 which illustrates a signal canceling and receiving unit scru 90 scru 90 is based on the structure of scu 30 fig3 but the processing unit 33 is modified to a processing unit 91 which provides additional output via a terminal 34 c c the output on terminal 34 c uses sensing function 31 and together with part of processing unit 91 serves as a line receiver similar to line receiver 12 a or 12 b thus scru 90 simultaneously performs two functions signal cancellation as does scu 30 and line receiver functionality as do line receivers 12 a and 12 b thus allowing the sensed signal or any function thereof to be output on the terminal 34 c and placed on the transmission line an example of an application using scru 90 is shown in fig1 for a network 100 network 100 is based on network 80 fig8 but scu 30 is replaced by scru 90 whose terminal c is connected to a data unit 16 f via a connection 102 scru 90 further is connected to transmission line 15 a 15 b 15 c and 15 d at junctions 101 a and 101 b in a manner similar to that of network 80 fig8 this configuration allows two isolated communication segments to use the transmission line simultaneously without interfering with each other one segment transports data over transmission line 15 a and 15.