Fujitsu Corporation

Nippon Telegraph and Telephone Corporation

Hiroshi Yamasaki

Yuji Maeda

Takahiro Hosokawa

Shigehiko Yazawa

Hiroyuki Kaneko

Hiroshi Nakaide

Hiroshi Takeo

Akio Morimoto

Satoshi Takeda

Masanori Kajiwara

Michinobu Ohhata

Takao Moriya

Noriaki Ohuchi

Ikuo Washiyama

Toshinari Kunieda

A failure detection system detects a failure of a package in a redundant system having a duplex package configuration. The failure detection system includes a first package including a signal processor for carrying out a predetermined signal processing on an input signal to the first package, where the first package is provided in each of first and second systems, a second package including a selector for selectively outputting an output signal of the signal processor of the first package in one of the first and second systems in response to a control signal, a failure detector for detecting a failure in the output signal of the signal processor of the first package in each of the first and second systems and for outputting a failure detection signal if the failure is detected, and a signal processor for carrying out a predetermined signal processing on the output signal of the selector, where the second package is provided in each of first and second systems, and a controller for supplying the control signal to the selector of the second package in each of the first and second systems based on the failure detection signal received from the second package in each of the first and second systems, so that the selector selectively outputs the output signal of the signal processor of the first package in an active one of the first and second systems. The controller includes a mechanism for disregarding the failure detection signal received from the second package during a predetermined time in response to a predetermined signal. This predetermined signal may indicate which one of the first and second systems is active or, indicate whether or not the second package of each of the first and second systems is mounted on a unit to which the first package of each of the first and second systems is mounted.

Signal processing apparatus including redundant first and second system

A method of monitoring abnormality of a clock driver in an electronic apparatus having a clock supply unit that supplies a clock signal and a plurality of function executing units to which the clock signal is inputted for executing prescribed functions at an identical clock, wherein each function executing unit is provided with a clock driver which, on the basis of the clock signal, oscillates internally to reproduce a clock signal, includes monitoring cut-off of an input clock signal and cut-off of an output clock signal of the clock driver, and outputting an alarm upon judging that the clock driver is abnormal in a case where the output clock signal has been cut off but the input clock signal has not. Alternatively, the method includes monitoring the phase of the input clock signal and the phase of the output clock signal of the clock driver, and outputting an alarm upon judging that the clock driver is abnormal in a case where the output clock signal has developed a phase shift, which is greater than a prescribed value, with respect to the input clock signal.

Apparatus for monitoring abnormality of each clock driver input and

A clock stoppage detector and a selector selection determining circuit are provided on each of a plurality of circuit boards. If any abnormality is detected in the clock selected in accordance with selector control information supplied from a clock selection controller provided common to the plurality of circuit boards, the selector selection determining circuit changes the selection independently of the selection control information. The selector selection determining circuit also performs clock selection independently when failure occurs to the clock selection controller.

Clock selection control device

Transmitting/receiving system includes a plurality of analog junction lines and analog tie trunks provided at two ends of the analog junction lines. The PBX is provided with an analog junction line-ISDN converting unit. The analog junction line-ISDN converting unit is operative to transfer B-channel signals on a first analog junction line through the PBX network and the analog tie trunks and to transfer D-channel signals on a second analog junction line.

Transmitting/receiving system having digital switching network

A digital signal transmission system includes a synchronization pattern detection circuit for detecting a synchronization pattern in response to a received transmitted digital signal, a pseudo synchronization detection circuit for detecting a pseudo synchronization pattern in the form of cyclic redundancy code in response to a received transmitted digital signal, and a synchronization protection circuit for counting the synchronization pattern detection signals produced when synchronization patterns are detected in response to a synchronization pattern detection signal from the synchronization pattern detection circuit. The synchronization protection circuit includes a main synchronization counter circuit and an auxiliary synchronization counter circuit. The count of protection steps for the confirmation of synchronization recovery of the auxiliary synchronization counter circuit in accordance with synchronization or asynchronization of the main synchronization counter circuit is variable.

Digital signal transmission system having frame synchronization operation

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Kawasaki, Japan

Hiroshi Yamasaki