21 EQUIPMENT FOR DIGITAL COMMUNICATION; TERMINAL EQUIPMENT FOR TELEGRAPH AND OTHER DATA TRANSMISSION SYSTEMS COMPRISING ERROR-CORRECTING ENCODERS AND DECODERS, MULTIPLEXERS, POWER SUPPLIES AND ANCILLARY COMPONENTS, AND COMPLETE TERMINALS COMPRISING THE AFOREMENTIONED ITEMS AND MODULATION SYSTEMS, SYNCHRONIZATION SYSTEMS, FREQUENCY STANDARDS, OSCILLATORS, SOLIDSTATE RELAYS, CHANNEL CONDITIONING EQUIPMENT AND CHANNEL MONITORING EQUIPMENT