Abstract: A synchronizing system in a digital communication line comprises a plurality of local switches for storing at least one digital line and monitoring a first piece of busy information when a clock source is already present, the local switches, if a first new clock source occurs while the first busy information is indicating no busy state, being capable of transmitting a master right request to turn the busy information to the busy state and to specify the first new clock source as a master clock and, on receiving a master right specification with respect to the master right request, being capable of outputting the first new clock source as the master clock; and a master switch connected to the plurality local switches in a star manner, by a link transmission line for transmitting control information including the master clock, master right request and master right specification, for monitoring a second piece of busy information indicating a busy state, the master switch, if a second new clock source occurs whil

Abstract: A transmission system for a key telephone system, in which speech signals and control signals are transmitted through two pairs of transmission conductors between a key service unit and each of a plurality of key telephone sets, and in which DC electric power is supplied from the key service unit to each of a plurality of telephone sets. In accordance with the present invention, the speech signal and the control signal are transmitted through a first transmission line of high frequency band provided by one pair of the transmission conductors from the key telephone set to the key service unit, and the speech signal and the control signal are transmitted through a second transmission line of high frequency band provided by the other pair of the transmission conductors from the key service unit to the key telephone set.

Abstract: A hybrid circuit, in which the differential output of an amplifier of the four-wire receive port having the differential output of low output impedance is connected to a series-connected circuit composed of a variable impedance circuit and the primary winding of a transformer connected to the two-wire port of the hybrid circuit, and in which the input of an amplifier of the four-wire transmit port of the hybrid circuit having a high input impedance is connected to the node connection of the variable impedance circuit and the primary winding of the transformer. In the case where the impedances of the variable impedance circuit and the transformer are in a state of mutual equilibrium, the neutral point potential of the amplifier of the four-wire receive port is applied as an input to the amplifier of the four-wire transmit port.