Supervisory system for network equipments

A supervisory system for supervising equipments communicating with each other via communication lines in a network, the supervisory system includes a plurality of supervisory devices, each of which devices is used for supervising a plurality of equipments in the network; and a controller for controlling the plurality of supervisory devices so that one of the plurality of supervisory devices performs a supervising operation for the plurality of equipments in the network. The controller includes a determination unit for determining whether or not each of the plurality of supervisory devices is operating normally; an instruction unit for supplying either a first instruction or a second instruction to each of the plurality of supervisory devices based on a determination result obtained by the determination unit, the first instruction indicating that a supervisory device to which the first instruction is supplied is to be active in the supervisory operation, the second instruction indicating that a supervisory device to which the second instruction is supplied is to be inactive in the supervisory operation; and a selecting unit for selecting from the plurality of supervisory devices a supervisory device to which the first instruction is supplied, so that the supervisory device selected by the selecting unit supervises the plurality of equipments in the network in accordance with the first instruction.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention generally relates to a supervisory system for network 
equipments, and more particularly to a supervisory system for gathering 
status information via lines from a plurality of network equipments 
communicated with each other in a network so as to survey the network 
equipments, the status information indicating status of each network 
equipment. 
Recently, a supervisory system for hierarchically surveying a plurality of 
network equipments dispersed in a network has been proposed. Due to this 
type of the supervisory system, maintenance works for the network can be 
effectively performed and the reliability of communication between network 
equipments in the network can be improved. 
(2) Description of the Related Art 
FIG.1 shows a supervisory system for hierarchically surveying a plurality 
of network equipments. Referring to FIG. 1, a plurality of network 
equipments 10 are connected with each other by a line 15 so that the 
communications between the network equipments 10 are performed via the 
line 15. Each of subordinate supervisory devices (SSV) 20(1) and 20(2) 
surveys connected to a plurality of network equipments 10, and a middle 
supervisory device 30 supervises the subordinate supervisory devices (MSV) 
20(1) and 20(2). Furthermore, the middle supervisory device 30 is 
supervised by an outranking system (OSS). In this system, each of the 
subordinate supervisory devices (SSV) 20(1) and 20(2) are centrally 
gathering performance data indicating changing of the status (e.g. a bit 
error rate) of the network equipments. The performance data is further 
transmitted from each of the subordinate supervisory devices (SSV) 20(1) 
and 20(2) to the middle supervisory device (MSV) 30. Then, the performance 
data is finally supplied from the middle supervisory device (MSV) 30 to 
the outranking system (OSS). 
The above supervisory system can be extended to a hierarchical supervisory 
system as shown in FIG. 2. Referring to FIG. 2, the hierarchical 
supervisory system has four hierarchies. The first hierarchy is provided 
with primary supervisory devices (P-SV) connected to network equipments 
(NE). The primary supervisory devices (P-SV) are set up in remote 
terminals. The second hierarchy is provided with regional supervisory 
devices (R-SV) connected to the primary supervisory devices (P-SV). The 
regional supervisory devices (R-SV) are set up in regions each of which 
regions includes one or a plurality of the remote terminals. The third 
hierarchy is provided with extensive supervisory devices (X-SV) connected 
to the regional supervisory devices (R-SV). The extensive supervisory 
devices (X-SV) are set up in zones each of which zones is formed of one or 
a plurality of regions. The fourth hierarchy is provided with a center 
supervisory device (C-SV) connected to the extensive supervisory devices 
(X-SV). The center supervisory device (C-SV) gathers the performance data 
from the network equipments (NE) via the primary supervisory devices 
(P-SV), the regional supervisory devices (R-SV) and the extensive 
supervisory devices (X-SV). The primary supervisory devices (P-SV) and the 
regional supervisory devices (R-SV) respectively correspond, for example, 
to the subordinate supervisory devices (SSV) and the middle supervisory 
devices (MSV) shown in FIG. 1. A system formed of the extensive 
supervisory devices (X-SV) and the center supervisory device (C-SV) 
corresponds, for example, to the outranking system (OSS). Each unit formed 
of the extensive supervisory device (X-SV) and the regional supervisory 
devices (R-SV) under the extensive supervisory device (X-SV) may 
correspond to the middle supervisory device (MSV) shown in FIG. 1. In this 
case, the center supervisory device C-SV corresponds to the outranking 
system (OSS). 
In the above system for hierarchically surveying a plurality of network 
equipments, as shown in FIG. 1, if a supervisory device (the SSV or the 
MSV) in any hierarchy is troubled, the performance data of the network 
equipments under the troubled supervisory device cannot be transmitted to 
the outranking system (OSS). It is thus desired that the outranking system 
(OSS) estimates trouble points in the network and estimates causes of the 
troubles based on the performance data gathered from the network 
equipments. In this case, a matter is a problem in which when a 
supervisory device in any hierarchy is troubled, the performance data from 
any part of the network equipments under the problem supervisory device 
cannot be gathered by the outranking system (OSS). 
SUMMARY OF THE INVENTION 
Accordingly, a general object of the present invention is to provide a 
novel and useful supervisory system for network equipments in which the 
disadvantages of the aforementioned prior art are eliminated. 
A more specific object of the present invention is to provide a supervisory 
system for network equipments in which system even if one supervisory 
device experiences problem in any hierarchy, information from the network 
equipments under the troubled supervisory device can be supplied to an 
outranking system. 
The above objects of the present invention are achieved by a supervisory 
system for supervising equipments communicated with each other via 
communication lines in a network, the supervisory system comprising: a 
plurality of supervisory devices, each of which devices is used for 
supervising a plurality of equipments in the network; and control means 
for controlling the plurality of supervisory devices so that one of the 
plurality of supervisory devices performs a supervising operation for the 
plurality of equipments in the network, wherein the control means 
comprises: determination means for determining whether or not each of the 
plurality of supervisory devices is normal; instruction means for 
supplying either a first instruction or a second instruction to each of 
the plurality of supervisory devices based on a determination result 
obtained by the determination means, the first instruction indicating that 
a supervisory device to which the first instruction is supplied is to be 
active in the supervisory operation, the second instruction indicating 
that a supervisory device to which the second instruction is supplied is 
to be inactive in the supervisory operation; and selecting means for 
selecting a supervisory device, to which the first instruction is 
supplied, from the plurality of supervisory devices, so that the 
supervisory device selected by the selecting means supervises the 
plurality of equipments in the network in accordance with the first 
instruction. 
According to the present invention, when a supervisory device performing 
the supervisory operation for the equipments in the network is troubled, 
the surpervisory device is changed to another supervisory device. Thus, 
even if one supervisory device is troubled in any hierarchy, information 
from the equipments under the troubled supervisory device can be supplied 
to an outranking system via the other supervisory device. 
Additional objects, features and advantages of the present invention will 
become apparent from the following detailed description when read in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A description will now be given, with reference to FIGS. 3 and 4, of the 
principle of a first embodiment of the present invention. 
A supervisory system according to the first embodiment hierarchically 
surveys a plurality of network equipments as shown in FIG. 1 or FIG. 2. In 
each hierarchy of the supervisory system, each supervisory device (SSV and 
MSV shown in FIG. 1 or P-SV, R-SV and X-SV shown in FIG. 2) is duplicated 
as shown in FIG. 3. Referring to FIG. 3, a first supervisory device SV#0 
and a second supervisory device SV#1 are connected to a supervisory device 
controller SVP by signal wires through each of which wires an on/off 
signal is transmitted. Each of the supervisory devices SV#0 and SV#1 
supplies to the supervisory device controller SVP a status signal S1 
indicating whether or not a corresponding supervisory device (SV#0 or 
SV#1) is normal. The status signal S1 being in an on-state indicates that 
a corresponding supervisory device is normal. The status signal S1 being 
in an off-state indicates that a corresponding supervisory device is not 
normal. The supervisory device controller SVP supplies a first control 
signal S2 to the first supervisory device SV#0. When the first supervisory 
device SV#0 is to be active in a supervisory operation and to be inactive 
therein, the supervisory device controller SVP maintains the first control 
signal S2, for example, in the off-state and in the on-state respectively. 
On the other hand, when the second supervisory device SV#1 is to be active 
in the supervisory operation and to be inactive therein, the supervisory 
device controller SVP maintains the second control signal S22, for 
example, in the on-state and in the off-state respectively. That is, the 
relationship between the on and off states of the first control signal S2 
and the activity and inactivity of the first supervisory device SV#0 is 
reciprocal to the relationship between the on and off states of the second 
control signal S22 and the activity and inactivity of the second 
supervisory device SV#1. 
The supervisory device controller SVP supplies a third control signal S3 to 
a switching device LSW. When the third control signal S3 is in the 
off-state, the switching device LSW selectively connects the first 
supervisory device SV#0 to communication lines for devices in upper and 
lower hierarchies. On the other hand, when the third control signal S3 is 
in the on-state, the switching device LSW selectively connects the second 
supervisory device SV#1 to the communication lines for the devices in the 
upper and lower hierarchies. 
The above signals S1, S2, S22 and S3 and meanings thereof are arranged as 
shown in the following Table-1. 
TABLE 1 
______________________________________ 
S1 ON : a corresponding SV is not normal 
OFF: a corresponding SV is normal 
S2 ON : SV#0 is active 
OFF: SV#0 is inactive 
S22 ON : SV#1 is inactive 
OFF: SV#1 is active 
S3 ON : SV#0 is selected 
OFF: SV#1 is selected 
______________________________________ 
Operations are performed as follows in a system as shown in FIG. 3. 
The supervisory device controller SVP is always monitoring the status 
signals S1 from the first and second supervisory devices SV#0 and SV#1. 
The supervisory device controller SVP controls states of the control 
signals S2, S22 and S3 with reference to the status signals S1 so that a 
supervisory device which is normal is always active and is connected by 
the switching device LSW to the communication lines for the devices in the 
upper and lower hierarchies in the supervisory system. The supervisory 
device (SV#0 or SV#1) connected to the communication lines for the devices 
in the upper and lower hierarchies gathers performance data of the network 
devices NE via the device in the lower hierarchy and supplies the 
performance data to the device in the upper hierarchy. 
When the supervisory device controller SVP is troubled, all the control 
signals S2, S22 and S3 are in the off-state. In this case, the first and 
second supervisory devices SV#0 and SV#1 are compulsorily activated and 
deactivated respectively and the first supervisory device SV#1 is 
compulsorily connected to the communication lines for the devices in the 
upper and lower hierarchies, as shown in FIG. 4. 
In the first embodiment of the present invention, even if one of the 
supervisory devices is troubled, the other supervisory device is connected 
to the communication lines for the devices in the upper and lower 
hierarchies. Thus, the performance data from the network equipments NE are 
continuously gathered by the other supervisory device. In addition, the 
relationship between the on and off states of the first control signal S2 
and the activity and inactivity of the first supervisory device SV#0 is 
reciprocal to the relationship between the on and off states of the second 
control signal S22 and the activity and inactivity of the second 
supervisory device SV#1. If a malfunction of the supervisory device 
controller SVP occurs, all the control signals S2, S22 and S3 are 
maintained in the off-state. Thus, in this case, one of the supervisory 
devices SV#0 and SV#1 and the other supervisory device are automatically 
activated and deactivated respectively. The activated supervisory devices 
is then automatically connected to the communication lines for the devices 
in the upper and lower hierarchies. That is, even if the malfunction of 
the supervisory device controller SVP occurs, the performance data from 
the network equipments NE are continuously gathered by the supervisory 
device automatically activated. 
A detailed description will now be given of the first embodiment of the 
present invention. 
A supervisory system according to the first embodiment of the present 
invention is formed as shown in FIG. 5. Due to the multiplex of the 
subordinate supervisory device SSV and the middle supervisory device MSV 
shown in FIG. 1, the supervisory system as shown in FIG. 5 is formed. 
Referring to FIG. 5, a subordinate supervisory device controller SSVP is 
connected to a first subordinate supervisory device SSV#0, a second 
subordinate supervisory device SSV#1, a subordinate switching device SLSW 
by signal wires for signals which may have on and off states. The 
subordinate supervisory device controller SSVP controls the first 
subordinate supervisory device SSV#0 and the second subordinate 
supervisory device SSV#1 so that a subordinate supervisory device which is 
normal is active and the other subordinate supervisory device is inactive. 
The subordinate switching device SLSW is controlled by the subordinate 
supervisory device controller SSVP so that the normal subordinate 
supervisory device (SSV#0 or SSV#1) is connected to network equipments NE 
and a middle switching device MLSW in the upper hierarchy. A middle 
supervisory device MSVP is connected to a first middle supervisory device 
MSV#0, a second middle supervisory device MSV#1 and a middle switching 
device MLSW. The middle supervisory device controller controls the first 
middle supervisory device MSV#0 and the second middle supervisory device 
MSV#1 so that a middle supervisory device which is normal is active and 
the other middle supervisory device is inactive. The middle switching 
device MLSW controlled by the middle supervisory device controller MSVP so 
that the normal middle supervisory device (MSV#0 or MSV#1) is connected to 
an outranking system OSS and the subordinate switching device SLSW in the 
lower hierarchy. 
Each of the subordinate supervisory devices and each of the middle 
supervisory devices (hereinafter simply referred to as a supervisory 
device SV) are formed as shown in FIG. 6. Referring to FIG. 6, a 
supervisory device SV has an SV processing portion 1, a timer interruption 
processing portion 2 and a signal analyzing portion 7. A processing level 
of the timer interruption processing portion 2 is less than that of the SV 
processing portion 1. The timer interruption processing part 2 is 
activated by an interruption from an internal timer 5 and writes data into 
a register 3. When the data is written in the register 3, a timer clear 
portion 4 is activated, so that the internal timer 5 is cleared by the 
timer clear portion 4. In a normal state, the timer interruption to the 
timer interruption processing portion 2 and the clearing of the internal 
timer 5 are repeated. However, if the timer interruption to the timer 
interruption processing portion 2 and the clearing of the internal timer 5 
are not performed due to a runaway of the SV processing part 1 or other 
malfunctions in the supervisory device SV, the internal timer 5 is not 
cleared and overflows. A time-over detection portion 6 outputs a status 
signal S1. The status signal S1 is being normally maintained in an 
on-state after the initial activation of the SV processing part 1. The 
status signal S1 is supplied to the supervisory device controller. When 
the time-over detection portion 6 detects that the internal timer 5 
overflows, the time-over detection portion 6 switches the status signal S1 
to be in an off-state. The signal analyzing portion 7 analyzes a control 
signal S2 or S22 supplied from the supervisory device controller SVP. The 
analyzing result obtained by the signal analyzing portion 7 is supplied to 
the SV processing portion 1. 
Each of the subordinate and middle supervisory device controller SSVP and 
MSVP (hereinafter simply referred to as a supervisory device controller 
SVP) is formed, for example, as shown in FIG. 7. Referring to FIG. 7, the 
supervisory device controller SVP has a first signal analyzing portion 11, 
a second signal analyzing portion 12 and a processing portion 13. The 
first signal analyzing portion 11 monitors and analyzes the status signal 
S1 supplied from the first supervisory device (SSV#0 or MSV#0, hereinafter 
simply referred to as SV#0). The second signal analyzing portion 12 
monitors and analyzes the status signal supplied from the second 
supervisory device (SSV#1 or MSV#1, hereinafter simply referred to as 
SV#1). The first and second signal analyzing portion 11 and 12 supply 
interruption signals to the processing portion 13 when the status signals 
S1 are changed from being in the on-state to being in the off-state and 
vice versa. 
When the interruption signal is supplied to the processing portion 13 from 
either the first signal analyzing portion 11 or the second signal 
analyzing portion 12, the processing portion 13 carries out a process as 
shown in FIG. 8. 
The processing portion 13 controls flags d1, j0 and j1. The flag d1 
indicates whether the first supervisory device SV#0 is active in the 
supervisory operation or the second supervisory device SV#1 is active in 
the supervisory operation. The flag jo indicates whether or not the first 
supervisory device SV#0 is normal. The flag j1 indicates whether or not 
the second supervisory device SV#1 is normal. The above flags d1, j0 and 
j1 are turned on and off in accordance with the following Table-2. 
TABLE 2 
______________________________________ 
d1 0 (off) : SV#0 is active 
1 (on) : SV#1 is active 
j0 0 (off) : SV#0 is normal 
1 (on) : SV#0 is not normal 
j1 0 (off) : SV#1 is normal 
1 (on) : SV#1 is not normal 
______________________________________ 
Referring to FIG. 8, in step 201, the flags j0 and j1 are respectively set 
based on the status signals S1 from the first and second supervisory 
devices SV#0 and SV#1. In step 202, it is determines whether the first 
supervisory device SV#0 or the second supervisory device SV#1 is active 
with reference to the flag d1. When it is determined that the first 
supervisory device SV#0 is active (d1=0) in step 202, the process is 
performed in accordance with steps 203 through 208. In step 203, the 
processing portion 13 determines whether or not the first supervisory 
device SV#0 is normal with reference to the flag j0. When it is determined 
that the first supervisory device SV#0 is normal (j0=0) in step 203, the 
process is completed. That is, the first supervisory device SV#0 
continuously gathers performance data from the network equipments NE. On 
the other hand, when it is determined that the first supervisory device 
SV#0 is not normal (j0=1) in step 203, the processing portion 13 further 
determines whether or not the second supervisory device is normal with 
reference to the flag j1 in step 204. When it is determined that the 
second supervisory device is not normal (j1=1) in step 204, the process is 
completed. That is, in this case, neither the first supervisory device 
SV#0 nor the second supervisory device SV#1 is normal, and the supervisory 
of the network equipments NE under the supervisory devices SV#0 and SV#1 
is interrupted. On the other hand, when it is determined that the second 
supervisory device SV#1 is normal (j1=0) step 204, the processing portion 
13 makes both the control signals S2 and S22 be in the on-state in steps 
205 and 206. Due to the control signals S2 and S22 being in the on-state, 
the first supervisory device SV#0 which is not normal and the second 
supervisory device SV#1 are respectively switched inactive and active (see 
Table-1). Then, in step 207, the processing portion 13 makes the control 
signal S3 be in the on-state. Due to the control signal S3 being in the 
on-state, the switching device (SLSW or MLSW, hereinafter simply referred 
to as LSW) switches from the first supervisory device SV#0 to the second 
supervisory device SV#1. Thus, the performance data from the network 
equipments NE is continuously gathered by the second supervisory device 
SV#1. After the control signal S3 is switched to the on-state in step 207, 
the flag d1 is set to "1" indicating that the second supervisory device 
SV#1 is active, in step 208. 
When, in step 202, it is determined that the second supervisory device SV#1 
is active (d1=1), the process is performed in accordance with steps 209 
through 214, in the same manner as steps 203 through 208. That is, when it 
is determined that the second supervisory device SV#1 and the first 
supervisory device SV#0 are respectively not normal and normal, in steps 
209 and 210, the processing portion 13 makes the control signals S2, S22 
and S3 be in the off-state in steps 211, 212 and 213. Thus, the first 
supervisory device SV#0 and the second supervisory device SV#1 are 
respectively switched being active and being inactive. Then, the flag d1 
is set to "0" in step 214. In this case, even if the second supervisory 
device SV#1 is troubled, the performance data from the network equipments 
NE is gathered by the first supervisory device SV#0. 
While the supervisory device controller SVP is carrying out the above 
process, the signal analyzing portion 7 in each of the first and second 
supervisory devices SV#0 and SV#1 carries out a process as shown in FIG. 
9. 
Referring to FIG. 9, the signal analyzing portion 7 determines, in step 
301, whether the control signal S2 to be supplied to the first supervisory 
device SV#0 or the control signal S22 to be supplied to the second 
supervisory device SV#1 is input thereto. When it is determined that the 
control signal S2 is input to the signal analyzing portion 7 in step 301, 
the signal analyzing portion 7 further determines whether or not the 
control S2 has been switched from the on-state to the off-state in step 
302. When it is determined that the control signal S2 has been switched 
from the on-state to the off-state in step 302, the signal analyzing 
portion 7 recognizes that the first supervisory device SV#0 must be 
switched from being inactive to being active. Thus, in step 304, the 
signal analyzing portion 7 restarts a CPU of the SV processing portion 1 
in the first supervisory device SV#0. On the other hand, it is determined 
that the control signal S2 is not switched from the on-state to the 
off-state in step 302, the signal analyzing portion 7 does not respond to 
the control signal S2. 
When it is determined that the control signal S22 is input to the signal 
analyzing portion 7 in step 301, the signal analyzing portion 7 further 
determines whether or not the control signal S22 has been switched from 
the off-state to the on-state in step 303. When it is determined that the 
control signal S22 has been switched from the off-state to the on-state in 
step 303, the signal analyzing portion 7 recognizes that the second 
supervisory device SV#1 must be switched from being inactive to being 
active. Thus, in step 304, the signal analyzing portion 7 restarts a CPU 
of the SV processing portion 1 in the second supervisory device SV#1. On 
the other hand, it is determined that the control signal S22 is not 
switched from the off-state to the on-state in step 302, the signal 
analyzing portion 7 does not respond to the control signal S22. 
When the CPU of the SV processing portion 1 is restarted, the supervisory 
device (SV#0 or SV#1) is switched from being inactive to being active. As 
a result, after the supervisory device gathers the performance data 
indicating the present state of the network equipments NE under the 
supervisory device, the supervisory for the network equipments NE are 
continuously performed. 
When a malfunction of the supervisory device controller SVP occurs, all the 
control signals S2, S22 and S3 are compulsorily maintained in the 
off-state "0". In this case, if the second supervisory device SV#1 has 
been active until the malfunction of the supervisory device controller 
occurs, due to the processes in steps 302 and 303, the first supervisory 
device SV#0 is automatically switched from being inactive to being active 
and the second supervisory device SV#1 is automatically switched from 
being active to being inactive. The first supervisory device SV#0 then 
gathers the performance data indicating the present state of the network 
equipments NE under the first supervisory device SV#0, and the supervisory 
for the network equipments NE are continuously performed by the first 
supervisory device SV#0. 
The SV processing portion 1 of the supervisory device SV carries out a 
process as shown in FIG. 10A. 
Referring to FIG. 10A, when the supervisory device SV is switched from 
being inactive to being active, the SV processing portion 1 makes the 
status signal S1 be in the on-state which state indicates the supervisory 
device SV is normal in step 401. Then, in step 402, the SV processing 
portion 1 performs a present state request processing for gathering the 
performance data indicating the present state of the network equipments NE 
under the supervisory device. After the present state request processing 
is completed in step 402, a normal supervisory process is carried out. In 
step 403, the SV processing portion 1 determines whether or not a request 
for gathering the performance data indicating the present state of the 
network equipments NE is supplied from a supervisory device in the upper 
hierarchy. If the request is supplied from the supervisory device in the 
upper hierarchy, the SV processing portion 1 performs the present state 
request processing in step 404 in the same manner as in step 402. When it 
is determined that the request is not supplied from the supervisory device 
in the upper hierarchy in step 403, or when the present state request 
processing is completed in step 404, the SV processing portion 1 
determines whether or not information indicating that the performance data 
for the network equipments NE has been changed is supplied from devices in 
the lower hierarchy in step 405. When it is determined that the 
information regarding the change of the performance data is supplied from 
the devices in the lower hierarchy in step 405, the SV processing portion 
1 updates the internal state thereof based on the new performance data for 
the network equipments NE in step 406. After this, the new performance 
data is sent from the SV processing portion 1 to a supervisory device in 
the upper hierarchy in step 407. On the other hand, when it is determined 
that the information regarding the change of the performance data for the 
network equipments NE is not supplied from the devices in the lower 
hierarchy in step 405, steps 406 and 407 are skipped. In the normal 
supervisory process, steps 403 through 407 are repeated. 
The present state request processing is performed in accordance with a flow 
chart shown in FIG. 10B. 
Referring to FIG. 10B, the SV processing portion 1 outputs a present state 
gathering request to the devices in the lower hierarchy in step 411. In 
response to the present state gathering request, the performance data 
indicating the present state of the network equipments NE are supplied to 
the SV processing portion 1 via the devices in the lower hierarchy in step 
411. The SV processing portion 1 updates the internal state thereof based 
on the performance data indicating the present state of the network 
equipments NE in step 413. Then, the performance data received by the SV 
processing portion 1 is transmitted to a device in the upper hierarchy in 
step 414. 
FIG. 11 shows examples of communication sequence in the supervisory system 
in three cases where a subordinate supervisory device SSV is changed to be 
active, a middle supervisory device is changed to be active, and the 
normal supervisory process is performed. 
Referring to FIG. 11, when a subordinate supervisory device SSV is changed 
to be active (1), the subordinate supervisory device SSV outputs the 
present state gathering request to the network equipments NE thereunder 
(2). The network equipments NE supply the performance data indicating the 
present state thereof to the subordinate supervisory device SSV (3) in 
response to the present state gathering request from the subordinate 
supervisory device SSV. When receiving the performance data, the 
subordinate supervisory device SSV updates the internal state based on the 
performance data (4). Then, the performance data indicating the present 
state of the network equipments NE is supplied from the subordinate 
supervisory device SSV to the middle supervisory device MSV in the upper 
hierarchy (5). When receiving the performance data from the subordinate 
supervisory device SSV, the middle supervisory device MSV updates the 
internal state based on the performance data (6). After that, the 
performance data indicating the present state of the network equipments NE 
is , supplied from the middle supervisory device MSV to the outranking 
system OSS (7). When receiving the performance data, the outranking system 
OSS updates the internal state based on the performance data (8). 
When the middle supervisory device MSV is changed to be active (9), the 
middle supervisory device MSV outputs the present state gathering request 
(10). The present state gathering request output from the middle 
supervisory device MSV is supplied to the network equipments NE via 
subordinate supervisory devices SSV coupled to the middle supervisory 
device MSV (10) (11)!. In response to the present state gathering 
request, the network equipments NE output the performance data indicating 
the present state thereof (12). The performance data indicating the 
present state of the network equipments NE is serially transmitted to the 
outranking system OSS via the subordinate supervisory devices SSV and the 
middle supervisory device MSV (12) (14) (16)!. The subordinate 
supervisory devices SSV, the middle supervisory device MSV and the 
outranking system OSS update the internal states thereof based on the 
performance data supplied from the lower hierarchy (13) (15) (17)!. 
In the supervisory system, when a supervisory device SV in any hierarchy is 
changed to be active, the performance data indicating the present state of 
the network equipments NE is always gathered, in accordance with the 
present state gathering request output from the supervisory device changed 
to be active, to the outranking system OSS via the supervisory devices in 
the lower hierarchies. Thus, even if a supervisory device SV in any 
hierarchy is trouble, the supervisory system can normally survey the 
network equipments NE continuously. 
In the normal supervisory process, when a state (e.g. an error bit rate) of 
a network equipment NE is changed, performance data indicating the 
changing state of the network equipment NE is supplied to a subordinate 
supervisory device SSV (18). The performance data indicating the changed 
state of the network equipment NE is further sequential transmitted from 
the subordinate supervisory device SSV to the outranking system OSS via 
the middle supervisory device MSV (20) (22)!. The subordinate supervisory 
device SSV, the middle supervisory device MSV and the outranking system 
OSS update the internal sate based on the performance data supplied from 
the lower hierarchy (19) (21) (23)!. 
In the above supervisory system, every time the state of the network 
equipments is changed, the performance data indicating the changed state 
is gathered to the outranking system OSS via the supervisory devices in 
the lower hierarchies. That is, the supervisory system always survey the 
network equipments NE. 
A description will be given, with reference to FIG. 12, of the principle of 
a second embodiment of the present invention. 
A supervisory system according to the second embodiment hierarchically 
surveys a plurality of network equipments as shown in FIG. 1 or FIG. 2. In 
each hierarchy of the supervisory system, each supervisory device (SSV and 
MSV shown in FIG. 1 or P-SV, R-SV and X-SV shown in FIG. 2) is duplicated 
as shown in FIG. 12. Referring to FIG. 12, a first supervisory device SV#0 
and a second supervisory device SV#1 are connected to a supervisory device 
controller SVP by communication lines (e.g. RS232C) through each of which 
lines data indicating messages is transmitted. The first and second 
supervisory devices SV#0 and SV#1 send status messages indicating whether 
or not the supervisory devices SV#0 and SV#1 are normal to the supervisory 
device controller SVP via the communication lines. The supervisory device 
controller SVP outputs response messages to the supervisory devices SV#0 
and SV#1 in response to the status messages. The supervisory device 
controller SVP outputs the control signal S3 in accordance with the status 
messages from the supervisory devices SV#0 and SV#1 to a switching device 
LSW. The switching device LSW carries out a switching operation in the 
same manner as that in the system shown in FIGS. 3 and 4. 
A detailed description will now be given of the second embodiment of the 
present invention. 
The a supervisory system according to the second embodiment of the present 
invention has the same structure as that according to the first embodiment 
as shown in FIG. 5. In each hierarchy, each supervisory device is 
duplicated as shown in FIG. 12. Each of the first and second supervisory 
devices SV#0 and SV#1 has an SV processing portion 21 and a message 
sending/receiving portion 22 as shown in FIG. 13. The message 
sending/receiving portion 22 operates in accordance with a flow chart 
shown in FIG. 14. 
Referring to FIG. 14, in step 501, the sending/receiving portion 22 sends 
the status message to the supervisory device controller SVP, and the 
message sending/receiving portion 22 receives data from the communication 
data line (the RS232C) in step 502. Then, in step 503, it is determined 
whether or not the received data obtained in step 502 is the response 
message from the supervisory device controller SVP. When the received data 
is not response message, a counter C is incremented by one in step 504 and 
it is determined whether or not the count value of the counter C reaches a 
predetermined value Co in step 505. In a case where the count value does 
not reach the predetermined value Co, the process in steps 502 through 505 
is repeated. In this process, when it is determined that the input data is 
the response message from the supervisory device controller SVP in step 
503, the message sending/receiving portion 22 determines whether or not 
the received response message is the same as that received in the last 
processing cycle in step 506. When the received response message is the 
same as that received in the last processing cycle, the process is 
completed, and the supervisory device SV is maintained in the present 
state (active or inactive). When the received response message differs 
from the recieved in the last processing cycle, the message 
sending/receiving portion 22 determines based on the received message 
whether the supervisory device SV is to be active or to be inactive in 
step 507. When it is determined that the supervisory device SV is to be 
active, the message sending/receiving 22 restarts the SV processing 
portion 21 so that the supervisory device SV is to be active in the 
supervisory operation. When it is determined that the supervisory device 
SV is to be inactive in step 507, the process is completed. 
On the other hand, when the count value of the counter C reaches the 
predetermined value Co before the response message from the supervisory 
device controller SVP is received, the process proceed from step 505 to 
step 508. In step 508, the message sending/receiving portion 22 determines 
whether or not this supervisory device is the first supervisory device 
SV#0. In a case of the first supervisory device SV#0, it is further 
determined whether or not the first supervisory device SV#0 is active in 
step 509. When the first supervisory device SV#0 is inactive, the message 
sending/receiving portion 21 restarts the SV processing portion of the 
first supervisory device SV#0 so that the first supervisory device SV#0 is 
changed to be active. If this supervisory device is the second supervisory 
SV#1 or if the first surpervisory device SV#0 is active, the process is 
completed. 
According to the above process, even if the response message is not 
received because a malfunction of the supervisory device controller 
occurs, the first supervisory device SV#0 automatically becomes active in 
the supervisory operation. 
The supervisory device controller SVP supplies to response messages to the 
supervisory devices SV#0 and SV#1 in accordance with a flow chart shown in 
FIG. 15. 
Referring to FIG. 15, in step 601, the supervisory device controller SVP 
sets in a register information (a flag) that the first supervisory device 
SV#0 is to be active in the supervisory operation. In step 602, a first 
flag counter (flg 0) is initialized to "0" and a second flag counter (flg 
1) is also initialized to "0". After that, the supervisory device 
controller SVP determines whether or not a status message from the first 
supervisory device SV#0 is received in step 603. If the status message 
from the first supervisory device SV#0 has been received, the first 
counter flag (flg 0) is maintained at "0" in step 604. Then, in this case, 
the process proceeds to step 609 via steps 606 and 608. In step 609, it is 
determined, based on the status message received and the information set 
in the register in step 601, whether or not the first supervisory device 
SV#0 or the second supervisory device SV#1 is to be active in the 
supervisory operation. Now, as the first supervisory device SV#0 is to be 
active, the process proceeds to step 610. In step 610, the supervisory 
device controller SVP then determines whether or not the first flag 
counter (flg 0) is "0". As the first flag counter (flg 0) is maintained at 
"0" in step 604, the supervisory device controller SVP supplies a first 
response message to the first and second supervisory devices SV#0 and SV#1 
in step 611. The first response message indicates that the first 
supervisory device SV#0 is to be active in the supervisory operation and 
the second supervisory device SV#1 is to be inactive in the supervisory 
operation. 
Every time the status message from the first supervisory device SV#0 is 
received, the above process is performed. Thus, the supervisory device 
controller SVP supplies the first response message (SV#0: active, SV#1: 
inactive) to the first and second supervisory devices SV#0 and SV#1 in 
response to the status message from the first supervisory device SV#0. 
On the other hand, when, in step 603, the supervisory device controller SVP 
determines that the status message from the first supervisory device SV#0 
is not received, the first flag counter (flg 0) is incremented by one in 
step 605. In this case, in step 610, it is determined that the first flag 
counter (flg 0) is not "0". Thus, the supervisory device controller SVP 
further determines whether or not the first flag counter (flg 0) exceeds 
"6" in step 612. When the first flag counter (flg 0) does not exceed "6", 
the supervisory device controller SVP supplies to the first response 
message to the first and second supervisory devices SV#0 and SV#1. During 
no status message from the first supervisory device SV#0, the above 
process is repeated until the first flag counter (flg 0) exceeds "6". When 
the first flag counter (flg 0) exceeds "6", the supervisory device 
controller SVP detects that the first supervisory device SV#0 has been 
troubled. The above process (steps 603 through 611) needs about 50 
milliseconds to complete one cycle thereof. That is, when the status 
message is not received for about 300 milliseconds (50 
milliseconds.times.6), the supervisory device controller SVP detects that 
the first supervisory device SV#0 has been troubled. 
When the supervisory device controller SVP detects that the first 
supervisory device SV#0 has been troubled, the process proceeds from step 
612 to step 613. In step 613, the control signal S3 is changed from to be 
in the off-state to be in the on-state. Based on the control signal S3 
being in the on-state, the switching device LSW is switched from the first 
supervisory device SV#0 to the second supervisory device SV#1 so that the 
second supervisory device SV#1 is coupled to the upper and lower 
hierarchies. The supervisory device controller SVP then sets information 
that the second supervisory device SV#1 is to be active in the supervisory 
operation in step 614, and the first flag counter (flg 0) is reset to "0" 
in step 615. After this, in step 616, the supervisory device controller 
SVP supplies a second response message to the first and second supervisory 
devices SV#0 and SV#1. The second response message indicates that the 
first supervisory device SV#0 is to be inactive in the supervisory 
operation and the second supervisory device SV#1 is to be active in the 
supervisory operation. 
In a state where the second supervisory device SV#1 is active and coupled 
to the upper and lower hierarchies by the switching device LSW, the 
supervisory device controller SVP sends the second response message (SV#0: 
inactive, SV#1: active) to the first and second supervisory devices SV#0 
and SV#1 in response to the receiving of the status message from the 
second supervisory device SV#1, in the same manner as in a case where the 
first supervisory device is active in the supervisory operation. In this 
case, if the status message from the second supervisory device SV#1 is not 
received for about 300 milliseconds, the supervisory device controller SVP 
detects that the second supervisory device SV#1 is troubled, in the same 
manner as in a case of the first supervisory device SV#0. That is, the 
process is carried out in accordance with steps 619 through 623 
corresponding to steps 612 through 616. As a result, the supervisory 
device to be active is switched from the second supervisory device SV#1 to 
the first supervisory device SV#0 by the switching device LSW and the 
supervisory device controller SVP supplies the first response message 
(SV#0: active, SV#1: inactive) to the first and second supervisory devices 
SV#0 and SV#1. 
The supervisory operation in the supervisory system according to the second 
embodiment is almost the same as that in the supervisory system according 
to the first embodiment indicated in FIGS. 10A, 10B and 11. 
A description will now be given of a third embodiment of the present 
invention. The supervisory system according to the third embodiment has a 
hierarchical structure as shown in FIG. 5, and, in each hierarchy, each 
supervisory device is duplicated as shown in FIG. 12. That is, each of the 
first and second supervisory devices SV#0 and SV#1 is connected to the 
supervisory device controller SVP by the communication line RS232C. 
The communication line RS232C includes signal wires DR (Data set Ready), ER 
(Data terminal Ready), RS (Request to Send) and CS (Clear to Send) and 
other signal wires. In the third embodiment, the above signal wires DR and 
CS are used for sending status signals and control signals between each of 
the supervisory devices SV#0 and SV#1 and the supervisory device 
controller SVP. The communication line RS232C between the first 
supervisory device SV#0 and the supervisory device controller SVP includes 
the signal wires DR(0) and CS(0). The communication line RS232C between 
the second supervisory device SV#1 and the supervisory device controller 
SVP includes the signal wires DR(1) and CS(1). In this case, on and off 
states of status signals transmitted from the supervisory devices SV#0 and 
SV#1 to the supervisory device controller SVP via the signal wires DR(0), 
DR(1), CS(0) and CS(1) are defined as shown in Table-3. The status signals 
correspond to the status signal S1 described in the first embodiment. 
TABLE 3 
______________________________________ 
IN DR(0) OFF : SV#0 is troubled 
ON : SV#0 is normal 
IN CS(0) OFF : SV#0 is troubled 
ON : SV#0 is normal 
IN DR(1) OFF : SV#1 is troubled 
ON : SV#1 is normal 
IN CS(1) OFF : SV#1 is troubled 
ON : SV# is normal 
______________________________________ 
The on and off states of control signals transmitted from supervisory 
device controller SVP to the supervisory devices SV#0 via the signal wires 
DR(0) and CS(0) are defined as shown in Table-4. The control signals 
correspond to the control signal S2 described in the first embodiment. 
TABLE 4 
______________________________________ 
IN DR(0) OFF : SV#0 is active 
ON : SV#1 is inactive 
IN CS(0) OFF : SV#0 is active 
ON : SV#0 is inactive 
______________________________________ 
The on and off states of control signals transmitted from supervisory 
device controller SVP to the supervisory devices SV#1 via the signal wires 
DR(1) and CS(1) are defined as shown in Table-5. The control signals 
correspond to the control signal S22 described in the first embodiment. 
TABLE 3 
______________________________________ 
IN DR(1) OFF : SV#1 is active 
ON : SV#0 is inactive 
IN CS(0) OFF : SV#1 is active 
ON : SV#0 is inactive 
______________________________________ 
The sending/receiving portion of the first supervisory device SV#0 operates 
in accordance with a flow chart shown in FIG. 16. 
Referring to FIG. 16, in steps 701 and 702, it is determined whether or not 
control signals transmitted from the supervisory device controller SVP 
through the signal wires DR(0) and CS(0) are in the on-state. When the 
control signals in both the signal wires DR(0) and CS(0) are in the 
on-state, the first supervisory device SV#0 sends the status message to 
the supervisory device controller SVP in step 703. After this, the first 
supervisory device SV#0 receives the response message output from the 
supervisory device controller SVP in response to the status message, in 
step 704. The first supervisory device SV#0 determines, based on the 
response message, whether or not the first supervisory device SV#0 is to 
be active in the supervisory operation in step 705. When it is determined 
that the first supervisory device SV#0 is to be active in step 705, the 
first supervisory device SV#0 further determines, in step 706, whether or 
not it was determined to be active in step 705 in the last processing 
cycle. When it was determined to be active in step 705 in the last 
processing cycle, the first supervisory device SV#0 is maintained to be 
active. On the other hand, when it was determined to be inactive in step 
705 in the last processing cycle, a flag is set to be active in step 707. 
After this, the first supervisory device SV#0 is restarted so as to be 
active in the supervisory operation. On the other hand, when it is 
determined based on the response message from the supervisory device 
controller SVP that the first supervisory device SV#0 is to be inactive, 
the flag is set to be inactive in step 709. 
If the supervisory device controller SVP breaks down, the control signals 
to be sent through the signal wires DR(0) and CS(0) are compulsorily 
changed to be in the off-state. In this case, the first supervisory device 
SV#0 determines that the control signals in signal wires DR(0) and CS(0) 
are in the off-state in steps 701 and 702. Then, the first supervisory 
device SV#0 further determines whether the flag is set to be active or to 
be inactive in step 710. When the flag is set to be active, the first 
supervisory device SV#0 is maintained to be active in the supervisory 
operation. On the other hand, when it is determined that the flag is set 
to be inactive in step 710, the flag is set to be active in step 711. The 
first supervisory device SV#0 is restarted in step 712 so as to be active 
in the supervisory operation. 
According to the process in steps 710 through 712, when the supervisory 
device controller SVP breaks down, the first supervisory device SV#0 is 
automatically changed to be active in the supervisory operation. 
The sending/receiving portion of the second supervisory device SV#1 
operates in accordance with a flow chart shown in FIG. 17. 
The second supervisory device SV#1 monitors the state of the control 
signals in the signal wires DR(1) and CS(1) in steps 701 and 702. When the 
second supervisory device SV#1 determines that the control signals in both 
the signal wires DR(1) and CS(1) are in the on-state, the process is 
performed in accordance with steps 703 through 709, in the same manner as 
the process in the first supervisory device SV#0. On the other hand, if 
the control signals in the signal wires DR(1) and CS(1) are in the 
off-state (the supervisory device SVP breaks down), the process is 
performed in steps 722 and 723. That is, it is determined whether the flag 
is set to be active or to be inactive in step 722. In a case where the 
flag is set to be inactive, the second supervisory device SV#1 is 
maintained to be inactive. When it is determined that the flag is set to 
be active in step 722, the flag is set to be inactive in step 723. The 
second supervisory device SV#1 is compulsorily changed to be inactive in 
the supervisory operation. That is, when the supervisory device controller 
SVP breaks down, the second supervisory device SV#1 is automatically 
changed to be in active. 
The supervisory device controller SVP operates in accordance with a flow 
chart shown in FIGS. 18 through 20. 
Referring to FIG. 18, in step 801, the supervisory device controller SVP 
determines whether or not the status message from the first supervisory 
device SV#0 is received. When the status message from the first 
supervisory device SV#0 is not received, a first counter (0) is 
incremented by predetermined value in step 806. It is then determined 
whether or not the the first counter (0) overflows in step 807. The above 
process in steps 801, 806 and 807 is repeated either until the status 
message is received or until the first counter (0) overflows. In this 
state, when the supervisory device controller SVP receives the status 
message from the first supervisory device SV#0, the supervisory device 
controller SVP further determines whether or not the status message is 
correct in step 802. When it is determined that the status message is not 
correct in step 802, the process proceeds from the step 802 to step 806. 
Thus, the increment of the first counter (0) described above is further 
repeated. When the status message is correct, the supervisory device 
controller SVP resets the first counter (0) to "0" in step 803. A first 
flag (flg SV#0) is set to be active in step 804. On the other hand, when 
the first counter (0) overflows, the first flag (flg SV#0) is set to be 
inactive in step 808. 
The supervisory device controller SVP detects whether or not the second 
supervisory device SV#1 is normal in accordance with steps 805 and 809 
through 814 corresponding to the above steps 801 through 804 and 806 
through 808. That is, when the correct status message from the second 
supervisory device SV#1 is received, a second flag (flg SV#1) is set to be 
active. On the other hand, the correct status message from the supervisory 
device SV#1 is not received, the second flag (flg SV#1) is set to be 
inactive. 
The process proceeds to step 815 shown in FIG. 19. Referring to FIG. 19, in 
step 815, the supervisory device controller SVP determines, with reference 
to the first and second flags, whether or not both the supervisory devices 
brake down. When at least either the first or second supervisory device 
SV#0 or SV#1 is normal, the supervisory device controller SVP further 
determines whether the first or second supervisory device SV#0 or SV#1 is 
active in the supervisory operation in step 816. When the first 
supervisory device SV#0 is active in the supervisory operation, the 
supervisory device controller SVP determines, based on the first flag (flg 
SV#0), whether or not the first supervisory device SV#0 is normal in step 
817 in step 817. When it is determined that the first supervisory device 
SV#0 is normal in step 817, the supervisory device controller SVP further 
determines whether or not the status signals in the signal wires DR(0) and 
CS(0) are in the on-state in steps 818 and 819. When the status signals in 
the signal wires DR(0) and CS(0) are in the on-state, the supervisory 
device controller SVP recognize that the first supervisory device SV#0 is 
normal. In this case, the supervisory device controller sends the first 
supervisory device SV#0 a response message indicating that the first 
supervisory device SV#0 is to be active in the supervisory operation in 
step 820. A response message indicating the second supervisory device SV#1 
is to be inactive in the supervisory operation is sent from the 
supervisory device controller SVP to the second supervisory device SV#1 in 
step 822. After this, the process returns to step 801 in the head point of 
the process. On the other hand, when the status signals in the signal 
wires DR(0) and CS(0) are in the off-state, the first flag (flg SV#0) is 
set to be inactive in step 821. After this the process returns to step 
815. 
When it is determined, in step 815, that both the first and second 
supervisory devices SV#0 and SV#1 break down, the process returns to step 
801 in the head point of the process. On the other hand, it is determined, 
based on the first flag (flg SV#0), that the first supervisory device SV#0 
is not normal in step 817, the process proceeds to step 823. 
In step 823, it is determined, based on the second flag (flg SV#1), whether 
or not the second supervisory device SV#1 is normal. When the second 
supervisory device is normal, the supervisory device controller SVP sends 
the second supervisory device SV#1 the response message indicating that 
the second supervisory device is to be active in the supervisory operation 
in step 824. An activity/inactivity flag is set, in step 825, so as to 
indicate that the second supervisory device SV#1 is active in the 
supervisory operation. The supervisory device controller SVP changes the 
control signal S3 to be in the on-state. Based on the control signal S3 
being in the on-state, the switching device LSW is switched from the first 
supervisory device SV#0 to the second supervisory device SV#1 in step 826. 
After this, the process returns to step 801 in the head point of the 
process. 
On the other hand, when it is determined that the second supervisory device 
SV#1 is active in the supervisory operation in step 816, the process 
proceeds to step 827 shown in FIG. 20. 
Referring to FIG. 20, in step 827, the supervisory device controller SVP 
determines, based on the second flag (flag SV#1), whether or not the 
second supervisory device SV#1 is normal. When it is determined that the 
second supervisory device SV#1 is normal in step 827. the supervisory 
device controller SVP further determines whether or not the status signals 
in the signal wires DR(1) and CS(1) are in the on-state in steps 828 and 
829. When the status signals in the signal wires DR(1) and CS(1) are in 
the on-state, the supervisory device controller SVP sends the second 
supervisory device SV#1 a response message indicating that the second 
supervisory device SV#1 is to be active in the supervisory operation in 
step 830. A response message indicating that the first supervisory device 
SV#0 is to be inactive is sent from the supervisory device controller SVP 
to the first supervisory device SV#0 in step 832. After this, the process 
returns to step 801 in the head point of the process. When the status 
signals in the signal wires DR(1) and CS(1) are in the off-state, the 
second flag (flg SV#1) is set to be inactive in step 831. After this, the 
process returns to step 815 shown in FIG. 19. 
On the other hand, it is determined, based on the second flag (flg SV#1), 
that the second supervisory device is not normal in step 827, the process 
is performed in accordance with steps 833 through 836 corresponding to 
steps 823 through 826 shown in FIG. 19. In the process in steps 833 
through 836, the first supervisory device SV#0 is changed to be active in 
the supervisory operation. 
The present invention is not limited to the aforementioned embodiments, and 
variations and modifications may be made without departing from the scope 
of the claimed invention.