Electrical computers and digital processing systems: multicomput – Computer-to-computer data routing – Alternate path routing
Reexamination Certificate
1998-07-10
2001-02-27
Maung, Zarni (Department: 2758)
Electrical computers and digital processing systems: multicomput
Computer-to-computer data routing
Alternate path routing
C709S225000
Reexamination Certificate
active
06195704
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a loop-type network system in which node devices are arranged in a loop, and to a method of controlling communication path thereof. In particular, it relates to a loop-type network system and controlling path thereof in which a data transmission path and a data reception path are separately established and a spare communication path is provided so as to make it possible to change paths immediately if a fault occurs, thus ensuring the availability of a communication path and improving the operability of the system.
BACKGROUND ART
As typical examples of conventional communications systems which have employed a loop-type network system in which node devices are arranged in a loop, the road control system, railway control system, sewerage control system, airport control system, river control system and underground railway control system have been known.
In these systems, a plurality of node devices are provided at each place and interconnected to each other. Data is transferred to the node devices and each node device is controlled on the basis of the data received.
Take a road control system for example. In the road control system, a control centre is installed within each control area, and video cameras, emergency telephones, vehicle sensors and other apparatus used in road surveillance are located along the roads. Information obtained from these apparatus is gathered on the control centre, where it is displayed on surveillance monitors.
Meanwhile, electronic signboards are also installed along the roads in order to display various road information, and communication routes are established for the purpose of transmitting the information (data) obtained by the aforementioned apparatuses to the display devices.
The control centre also gathers information on accidents and traffic congestion from adjoining areas, and various judgments are made on the basis of the gathered information and information from the area itself. The results are displayed on the electronic signboards in the form of information on traffic congestion and various other types of guidance, thus helping to control the traffic.
FIG. 9
illustrates a road control system of this kind. The system comprises a plurality of node devices
10
-
1
through
10
-
8
, and a communication route
40
which connects the node devices
19
-
1
through
10
-
8
so as to transmit and receive information therebetween.
Specifically, in
FIG. 9
,
10
-
1
is a control centre or a node device located in the control centre or each place, while
20
-
1
through
20
-
8
are local communication devices such as video cameras, emergency telephones, vehicle sensors, electronic signboards or monitors.
30
is a communication path control device (console), which controls the communication path in relation to the node devices
10
-
1
through
10
-
8
.
In the system configured in this manner, the communication paths in relation to the node devices
10
-
1
through
10
-
8
are established through the control by the communication path control device
30
. Meanwhile,
40
is an optical cable which constitutes the communication path, assuming the form of a loop which serves to transmit data between the local transmission devices by way of the plurality of node devices
19
-
1
through
10
-
8
.
Recent years have witnessed the development of transmission systems of this sort which make use of the ATM (asynchronous transfer mode) exchange method and in which the communication path is established in the ATM exchange method.
FIG. 10
is a simplified version of
FIG. 9
, and will be used for the purpose of describing a path control system using the ATM exchange method.
In the conventional system configured as illustrated in
FIG. 10
, the communication path through which data (e.g., to display on a surveillance monitor screen images of traffic congestion picked up by a video camera) is transmitted between local communication devices
21
-
1
and
21
-
2
is connected at the node devices
15
,
16
,
17
by way of a single route of a bidirectional path with data transmission and data reception using the same VPI/VCI (virtual path/virtual channel) data.
However, there is a problem in establishing communication paths in a loop-type network as described above in that it is difficult to operate the communication paths if a system fault occurs.
For instance, as shown in
FIG. 11
, if a fault occurs in one of the node devices or in the optical cable which connects the node devices, the whole of the communication route associated with the faulty section is blocked. As a result, data transmission becomes impossible and the system ceases to operate. Thus, the occurrence of a fault on the communication route which forms the loop in a loop-type network is fatal for the operation of the system.
Moreover, when a diversion path is to be established onto a route which is unaffected by the fault, it is necessary to re-establish the communication paths to all the node devices, and after the fault has been repaired and service resumed, the communication paths to all the node devices must be checked. This means that the system will be inoperative for a long time, leading to a lowering of the control function. In the road control system designed to work night and day, this long inoperative time of the system will create severe disruption and cause panic in traffic.
As described above, the conventional network path establishing method is configured based on a path control method in which the communication path between local communication devices runs round the loop in such a manner that the transmission and reception paths follow the same route. With such a configuration, the occurrence of a fault will make data transmission impossible, and depending on the spot where fault occurs, it may be necessary to re-establish diversion routes for all the communication paths connected with that spot. In a system such as the road control system where transmission defaults at the outdoor location may occur at high probability, the communication path has to be disrupted in a long time at any times, and a great deal of work is required in order to re-establish a diversion route.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a loop-type network system and a method of path control for the network system, which make it possible to change route immediately if a fault occurs, thus ensuring the availability of a communication path and improving the operability of the system.
With a view to achieving the abovementioned object, the present invention provides a loop-type network system in which a plurality of node devices housing terminals are provided and communication paths between the terminals are established by the node devices so as to realise bidirectional communication between the terminals, the network system including a communication path control device for controlling the connection of the communication paths to the node devices, which is characterised in that a communication path between the terminals is established by establishing a transmission path and a reception path in separate routes, while establishing a loop-shaped spare communication path in a direction opposite to a direction of a loop route formed by the transmission path and the reception path.
The node devices may employ the asynchronous transfer mode exchange method.
The spare communication path may utilise the same virtual path and virtual channel as in the transmission path and the reception path established by the separate routes.
Further, the present invention provides a method of path control in a loop-type network system in which a plurality of node devices housing terminals are provided and communication paths between the terminals are established by the node devices so as to realise bidirectional communication between the terminals, the network system including a communication path control device for controlling the connection of the communication paths to the node devices, which is characterised in that the method comprises the s
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Maung Zarni
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