G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
G08C19/00—Electric signal transmission systems
G08C19/16—Electric signal transmission systems in which transmission is by pulses
H—ELECTRICITY
H04—ELECTRIC COMMUNICATION TECHNIQUE
H04Q—SELECTING
H04Q1/00—Details of selecting apparatus or arrangements
H04Q1/18—Electrical details
H04Q1/30—Signalling arrangements; Manipulation of signalling currents
H04Q1/44—Signalling arrangements; Manipulation of signalling currents using alternate current
H04Q1/442—Signalling arrangements; Manipulation of signalling currents using alternate current with out-of-voice band signalling frequencies
H04Q1/4426—Signalling arrangements; Manipulation of signalling currents using alternate current with out-of-voice band signalling frequencies using two or more signalling frequencies, transmitted in succession or simultaneously