Electronic exchange apparatus synchronized with digital network

Details Electronic exchange apparatus synchronized with digital network Electronic exchange apparatus synchronized with digital network

1989-06-28

1991-12-31

Olms, Douglas W.

Multiplex communications

Wide area network

Packet switching

3701051, H04J 306

Patent

active

050777343

ABSTRACT:
A private branch exchange includes an oscillator for generating a reference clock defining the transmission frequency of a digital network, a clock generating circuit for generating a clock, whose frequency is slightly higher than that of the reference clock, in synchronization with the clock extracted from the digital network, and a selector which monitors whether or not the clock generating circuit is in a state in which it can operate properly, selects the output of the clock generating circuit when it is normal or the output of the oscillator when it is abnormal, and applies the selected output as a drive clock to a time-division switch for performing time-division multiplex transmission while keeping frame synchronization with the digital network. The clock generating circuit comprises an oscillator for generating a clock of a frequency which is slightly higher than that of the reference clock to such an extent as to allow the frame synchronization, and a gate circuit which is enabled in synchronization with the clock extracted from the digital network and disabled upon completion of the exchange of one-frame-signal to provide the output of the oscillator to the selector as a drive clock.

REFERENCES:
patent: 3384821 (1968-05-01), Beck
patent: 3962541 (1976-06-01), Seidel
patent: 4002845 (1972-01-01), Kaul et al.
patent: 4744081 (1988-05-01), Buckland
patent: 4876683 (1989-10-01), Sazuki
patent: 4953195 (1990-08-01), Ikemori

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