Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SEGMENT SWITCHING APPARATUS
BACKGROUND OF THE INVENTION
Field of the Invention
A VP (Virtual Path) between a transmitting end and a
receiving end is usually configured by a plurality of
segments . If a fault occurs in a certain segment , the segment
is recovered from the faulty state by switching the segment
to a standby segment serving as a spare of the above segment .
The present invention relates to a segment switching
apparatus for switching segments in the above case.
Description of the Related Art
FIG. 3 is a schematic diagram showing an end-end VP to
which the present invention is applied. The VP a.s configured
by a segment 1, a segment 2, and a segment 3, in which the
segment 1 controls a carrier A, the segment 2 controls a
carrier B, and the segment 3 controls a carrier C. The
segment 1 includes nodes 1 and 2 , the segment 2 includes nodes
3 and 4, and the segment 3 includes nodes 5 and 6.
It is assumed that the segment 2 causes a trouble between
the nodes 3 and 4.
Setting one of two nodes in the segment nearby the
proximal end of the segment and the other nearby the distal
end of the segment is preferable to switch the segments.
In ATM (Asynchronous Transfer Mode) , OAM (Operation and
Maintenance ) function has been executed by using a segment
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OAM (Operation and Maintenance) cell. The segment OAM cell
is a cell for terminating in the segment concerned by setting
3 as a VCI { identifier of VC ( Virtual Channel ) } and 4 is set
as the OAM cell for executing the OAM function of the end-end
VP as the VCI.
As for the conventional method using the OAM cell, it
is necessary to insert a new OAM cell in order to perform
a switching message between segments when a trouble occurs .
Therefore, a circuit for inserting/detecting the OAM cell
is required.
Moreover, there is not any assurance that the band of
a transmission line is assigned to transmit an OAM cell and
thus, it is apprehensive that transfer of a message may be
delayed.
Resultantly, there were problems that more processing
circuits were necessary for switching, and a lot of
processing time was required, and switching was delayed.
SUMMARY OF THE INVENTION
The present invention is made to solve the above problems
and its object is to provide an apparatus capable of repairing
a fault detected in a segment in the same segment.
It is another object of the present invention to provide
an apparatus for starting a repair operation in the
most-upstream segment among segments in which a fault is
detected, but for preventing a segment at the downstream side
of the most-upstream segment from starting the repair
operation.
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To attain the above objects, an apparatus of the present
invention has a fault detecting function for detecting a
fault every segment, an operation control function for
controlling the time until staring a fault repair operation
after detecting a fault, and a repair circuit for repairing
a fault after controlling operations by the operation control
function and performs the fault repair operation every
segment.
In FIG. 3, if a fault occurs in the path between the
nodes 3 and 4 of the segment 2 , the fault is similarly detected
in accordance with the fault detecting function of the nodes
4, 5, or 6.
However, because the set time of a timer for starting
the operation of the operation control function of the node
4, 5, or 6 is set to a value to be decreased toward
more-upstream node, the fault repair operation is first
performed in the most-upstream node 4 but the operation is
not repeated in the node 5 or 6.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a basic embodiment
of the present invention;
FIG. 2 is a block diagram showing an embodiment more
specific than the embodiment of FIG. 1;
FIG. 3 is a schematic diagram showing a path to which
the present invention is applied;
FIG. 4 is a schematic diagram showing a result when the
present invention is applied to repair a fault of the path
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shown in FIG. 3;
FIG. 5 is a block diagram showing another embodiment
of the present invention; and
FIG. 6 is a block diagram showing still another
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will be described
below by referring to the accompanying drawings.
FIG. 1 is a block diagram showing an embodiment of the
present invention.
In FIG. 1, symbol 1-1 denotes a segment switching
apparatus of the present invention, 1-2 denotes an external
signal to be inputted, 1-3 denotes a fault detecting
function, 1-4 denotes an operation control function, 1-5
denotes an operation control signal, 1-6 denotes a repair
circuit, and 1-7 denotes an output signal.
The fault detecting function 1-3 detects a fault by
monitoring the input external signal 1-2.
For example, by deciding so as to transmit a dummy cell
to be transmitted between ends of the path in the time zone
when a user' s message is not present between the ends of the
path, the cell is detected as a fault when the external signal
1-2 is stopped.
When an external signal is stopped and a fault is
detected by the node 4 of FIG. 3, the same fault is detected
by nodes ( in this case, nodes 5 and 6 ) more downstream than
the node 4.
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However, it is necessary to perform the fault repair
operation by the repair circuit 1-6 of the node 4 and to
prevent the operation from being repeated in the node 5 or
6.
The operation control function 1-4 is used to avoid a
repetitive operation. Because of the existence of this
function, the repair circuit 1-6 of the node 4 first operates.
It is possible to most simply realize the operation
control function 1-4 of FIG. 1 by the guard time setting means
of a timer.
FIG. 2 is a block diagram showing the embodiment of FIG.
1 by further embodying it. Symbols 2-1, 2-2, 2-3, 2-5, 2-6,
and 2-7 in FIG. 2 denote portions same as denoted shown by
symbols 1-1, 1-2, 1-3, 1-5, 1-6, and 1-7 of FIG. 1, and the
guard time setting means 2-4 of FIG. 2 corresponds to the
operation control function 1-4 of FIG. 1.
When the fault detecting function 2-3 of the segment
switching apparatus 2-1 detects a fault, it sets a timer (not
illustrated) in the guard time setting means 2-4. When the
fault detecting function 2-3 still detects a fault after the
set time of the timer elapses, the control signal 2-5 is
outputted to operate the repair circuit 2-6.
By setting the guard time to be set to the timer of the
guard time setting means 2-4 so that it increases toward a
more downstream node, the repair operation has been completed
in an upstream node when the set time of the timer elapses
in a downstream node and a fault is not detected in accordance
with a downstream fault detecting function. Therefore, any
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repair operation is not repeated.
When the repair operation is not completed in an upstream
node within a predetermined time, a fault is detected in
accordance with the fault detecting function of a downstream
node also when the set time of the timer elapses in the
downstream node and the operation of the repair circuit of
the downstream node is started.
FIG. 5 is a block diagram showing another embodiment
of the present invention. In FIG. 5, symbols 5-l, 5-2, 5-3,
5-5, 5-6, and 5-7 denote portions same as those denoted by
symbols 2-1, 2-2, 2-3, 2-5, 2-6, and 2-7 in FIG. 2 and a signal
correction means 5-4 transmits, for example, a dummy cell
as an output signal 5-7 to prevent the fault detecting
function of a downstream node from detecting a fault.
That is, while a fault is not detected in accordance
with the fault detecting function 5-3, the input signal 5-2
passes through the repair circuit 5-6 and signal correction
means 5-4 without stopping and serves as the output signal
5-7. When the fault detecting function 5-3 detects a fault
(for example, when the function 5-3 detects that input
signals are stopped), it immediately operates the repair
circuit 5-6 and simultaneously transmits a signal (dummy
signal designated with end-end transmission) generated by
the signal correction means 5-4 as the output signal 5-7.
Because the above dummy signal is inputted as the input
signal of a downstream node, it is detected by a downstream
node as if no fault occurs .
When an upstream node does not succeed in fault repair,
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the operation of the signal correction means 5-4 of the node
is stopped. Because an input signal disappears in the
downstream node, a fault is detected in accordance with the
fault detecting function of the node.
As for the embodiments shown in FIGS . 1, 2 , and 5 , the
fault detecting functions ( 1-3 , 2-3 , and 5-3 ) and the repair
circuit s ( 1- 6 , 2 - 6 , and 5 - 6 ) are provided in the same node .
This is an example that the fault-detecting node and
switching node shown in FIG. 6A are the same node.
However, as shown in FIG. 6B, it is also possible to
provide a switching node to a node immediately downstream
than a fault detecting node. In this case, to prevent a
duplicate operation from being performed due to a fault
detected by a fault detecting node downstream than the above
fault detecting node, it is possible to use the guard time
setting means 2-4 of FIG. 2 and moreover, it is possible to
prevent a fault from being detected by a downstream node by
using the signal correction means 5-4 of FIG. 5. Moreover,
a switching notification signal corresponding to the
operation control signal 2-5 or 5-5 of FIG. 2 or 5 is
transmitted to a switching node.
Because this switching notification signal is a
notification addressed to a node immediately downstream than
a fault detecting node, it does not reach a switching node
downstream than the addressed node. When repair is not
completed in the switching node, a switching notification
signal is transmitted from the switching node to a switching
node immediately downstream than the former switching node.
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It is possible to properly generate a dummy signal to
be transmitted from the signal correction means 5-4 or a
switching notification signal to be transmitted from the
fault detecting node of FIG. 6B to a switching node in
accordance with the specification of an ATM cell.
Moreover, a method of superimposing switching
information on a user cell is proposed ( Japanese Unexamined
Patent Publication No. 10-173679). Furthermore, it is
possible to form a cell configuration in which switching
information is superimposed on a dummy signal, the
destination node of a switching notification signal detects
the switching information as a switching signal, and other
nodes recognize the switching information as a mere dummy
cell.
The repair operation performed by the repair circuit
1-6, 2-6, or 5-6 or the repair operation in a switching node
is a repair operation for mainly performing switching to a
standby segment. A standby path and a standby segment are
previously assigned to each VP (virtual path) and each
segment. Therefore, if a fault occurs in a current path or
current segment, it is possible to switch the current path
or segment to a standby path or segment.
As previously described for FIG. 3, if a fault occurs
between the nodes 3 and 4 in the segment 2, the fault is
detected in accordance with the fault detecting function of
the node 4. When the repair circuit of the node 4 operates
and the fault is repaired, the portion between the nodes 3
and 4 is switched to a standby segment.
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FIG. 4 is a schematic diagram showing the switching
result of repairing the fault shown in FIG. 3. In FIG. 4,
a symbol same as that in FIG. 3 denotes the same portion.
FIG. 4 shows a state in which the portion between the nodes
3 and 4 is switched to a standby segment.
As shown in FIG. 4, it is also possible to switch the
portion between the nodes 6 and 1 to a standby path. However,
switching to a standby segment is a preferred method in order
to effectively use resources.
As for the above embodiments, a segment switching
apparatus is described which is set nearby the proximal end
and distal end of each of a plurality of segments mainly
configuring a virtual path. However, it is needless to say
that the present invention can use a segment switching
apparatus to be set nearby the proximal end and the distal
end of each of a plurality of segments configuring a path.
As described above, according to the present invention,
a fault is detected in a segment configuring a path and the
segment is switched to a standby segment to perform repair
operation, but segments downstream than the segment causing
the fault do not relate to the fault. Therefore, it is
possible to quickly execute the repair operation when a fault
occurs and moreover, repair the fault by making most use of
network resources.
Moreover, it is unnecessary to newly prepare any special
band for transmitting OAM cells like the conventional case
of using OAM cells.
Furthermore , because the circuits shown in FIGS . 1 , 2 ,
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and 5 are easily changed to an LSI, there is an advantage
that an apparatus of the present invention can be downsized.
