Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Redundant
Reexamination Certificate
1998-04-06
2001-04-03
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Redundant
C327S551000
Reexamination Certificate
active
06211724
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electronic switching system; and, more particularly, to a duplex board system with a glitch cancellation circuit.
BACKGROUND OF THE INVENTION
In an electronic switching system, for instance, two main boards for call processing are dualized to construct a duplex board system for system reliability. The duplex board system includes two boards which are functionally identical each other, one of the boards, which is in an active state, performing the function thereof while the other is in a standby state. The stand-by-state board takes over the function of the active state board when the active board fails to function properly due to a defect developed therein.
Referring to
FIG. 1
, there is provided a conventional duplex board system
10
which comprises two identical processing boards, a side_A board
1
and a side_B board
2
.
A state signal ACT*_A through a line L
1
depicts the state of the side_A board
1
, wherein * denotes that a logic low state depicts the active state. And the state signal ACT*_B through the line L
2
depicts the state of the side_B board
2
.
It is assumed that the side_B board
2
currently performs the call processing in the active state, i.e., the ACT*_B presents a logic low, and the side_A board
1
has been installed now. When power is applied to the side_A board
1
from a power supply (not shown), the state of the side_A board
1
becomes at first stand-by, i.e., the ACT*_A shows a logic high.
If a defect is developed within the side_B board
2
, the ACT*_B becomes logic high to represent the stand-by state. When the side_A board
1
receives the state signal ACT*_B of the stand-by, the side_A board
2
shifts to the active state, i.e., the ACT*_A becomes logic low. Therefore, the side_B board
2
can be removed from the whole system to repair the fault therein, without interrupting the call processing since the counterpart side_A board
1
takes over the call processing. The side_B board
2
is installed after being repaired and waits in the stand-by state as did the side_A board
1
before.
However, when one of the boards, e.g., the side_A board
1
, is removed or installed, the state signal ACT*_A may have a glitch period which makes an undesirable state transition at the counterpart board. Accordingly, it is desirable to minimize or prevent the glitch period of the state signal between the boards of the duplex board system.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to provide a duplex board system for preventing an undesirable state transition generated by a glitch period of state signals between two boards of the duplex board system.
In accordance with the present invention, there is provided a duplex board system comprising:
two functionally identical processing boards, one of the boards being in an active state and the other being in a stand-by state, each of the boards generating a state signal depicting the state thereof, wherein the stand-by state board succeeds the active state board when the active state board becomes deactivated; and
two cancelling units, each coupled between the two boards for receiving the state signal from one of the boards, suppressing a glitch period from the state signal generated at said one of the boards, the glitch period representing an unstable signal level transition of the state signal, and outputting the glitch suppressed state signal to the other board.
REFERENCES:
patent: 4635249 (1987-01-01), Bortolini et al.
Bacon & Thomas PLLC
Daewoo Telecom Ltd.
Wells Kenneth B.
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