Communication method and apparatus

A communication apparatus comprising:

• terminal means for connection to a 2-wire transmission line;
• transmission means connected to said terminal means for controlling an analog value of a first signal on said transmission line for transmitting analog data over said transmission line and for superimposing upon said analog value a digital signal for transmitting digital data over said transmission line, said transmission means comprising an analog control device and a digital processor connected thereto for controlling the analog value of said first signal;
• and,
• receiving means connected to said terminal means for receiving an analog value of a signal on said transmission line, said analog value having a value in accordance with analog data received, and for receiving digital data superimposed upon the analog value of the received analog data.

A communication system comprising:

• a 2-wire transmission line;
• a first communication apparatus connected to said transmission line for transmitting a line current over said transmission line, said line current having an analog value in accordance with analog data to be transmitted by said first communication apparatus and having superimposed thereon digital data also transmitted by said first communication apparatus;
• and,
• second communication apparatus connected to said transmission line for controlling a voltage across said transmission line, said voltage being controlled at an analog value representing analog data to be transmitted by said second communication apparatus, said second communication apparatus superimposing digital data on the analog value of the line voltage in accordance with digital data to be transmitted by the second communication apparatus.