Multiplex communications – Fault recovery
Reexamination Certificate
1999-07-07
2004-01-20
Ton, Dang (Department: 2666)
Multiplex communications
Fault recovery
C370S217000
Reexamination Certificate
active
06680903
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for automatically selecting an alternative master node from slave nodes when a failure occurs at a master node and a method for specifying a location of a failure such as line disconnection or a node failure and recovering from the failure, in a network system in which the master node and at least one slave node are present, and the master node transmits a specific signal pattern, which is received by every node at regular time intervals within a fixed time period, and a network system in which specifying the location of the failure and recovering from the failure are implemented.
BACKGROUND OF THE INVENTION
In a conventional network system in which a master node and slave nodes are present, and the master node which arbitrates a data transmission right is required for data transmission, when a failure occurs at the master node, data communication becomes impossible.
Meanwhile, in a method for detecting a location of a failure in the conventional network system, for example, as disclosed in Japanese Published Patent Application No. Syo 56-161742, in a loop-type network, when a no-carrier state continues during more than a fixed time period, each node which has detected the no-carrier state outputs its carrier, and after specified time elapses, a slave node outputs a response including its node address by means of its carrier, whereby the master node recognizes that there exists a failure before the slave node which output this address.
Hereinafter, this method (Japanese Published Patent Application No. Syo 56-161742) will be described with reference to FIG.
12
.
FIG. 12
shows an example of the loop-type network. In
FIG. 12
, reference numeral
12
a
denotes a main station,
12
b
,
12
c
,
12
d
, and
12
e
denote terminal stations, and
12
f
denotes a line. In a normal state, the main station
12
a
sends a carrier to the terminal station
12
b
. With this carrier, data is transmitted. The terminal stations
12
b
-
12
e
receive, reproduce, and relay this carrier. In the normal state, the nodes
12
b
,
12
c
,
12
d
, and
12
e
and the main station
12
a
receive and detect the carrier.
As shown in
FIG. 12
, when a failure occurs on a line between the terminal stations
12
b
and
12
c
, the terminal stations
12
c
,
12
d
, and
12
e
, and the main station
12
a
detect the no-carrier state, although the terminal station
12
b
does not detect the no-carrier state, because it receives the carrier normally.
Upon detecting the no-carrier state, each station outputs its carrier after Ta time has elapsed. Therefore, the terminal stations
12
d
,
12
e
, and the main station
12
a
can detect the carrier again. The station which has detected the carrier stops sending its carrier. However, since the failure has occurred on the line between the terminal stations
12
b
and
12
c
, the terminal
12
c
continues detecting the no-carrier state.
Hence, the terminal station
12
c
prepares for outputting a line down response after Tb time period after outputting its carrier. After Tc time period, the terminal station
12
c
repeats outputting the line down response including its address at time intervals of Td by means of its carrier. The main terminal
12
a
receives the line down response from the terminal
12
c
, thereby detecting there is line disconnection between the terminal station
12
c
and the terminal station
12
b.
In this method, however, when a network is not of a loop type, the location of the failure cannot be specified if occurrence of the failure is detected by detecting the no-carrier state, depending upon construction of the network.
Turning now to
FIG. 13
, there is shown a network system disclosed in Japanese Published Patent Application No. Hei. 10-113459, in which at least one loop comprising plural loop-connected nodes and at least one loop comprising either a single node or plural loop-connected nodes are directly connected to a common transmission line. Using this network system, two cases, that is, a case where a line disconnection failure occurs between nodes
112
and
111
, and a case where a node failure occurs at a master node
101
, will be discussed below.
When the line disconnection failure has occurred between the nodes
112
and
111
, the nodes
111
and
110
respectively detect the no-carrier state and thereby detect that the failure has occurred. If each of the nodes
111
and
110
which have detected the failure, outputs its carrier, the carrier output from the master node
101
and the carrier output from the node
110
collides on the common communication line
15
, and thereby the carrier (from the nodes
111
and
110
) is not received normally. As a consequence, the location of the failure cannot be detected/specified.
When the node failure has occurred at the master node
101
and thereby the master nodes
101
stops outputting the carrier, nodes other than the master node
101
, i.e., the nodes
100
,
110
,
111
,
112
,
120
, and
121
, detect the no-carier state and thereby detect that the failure has occurred. If the nodes
100
,
110
,
111
,
112
,
120
, and
121
which have detected occurrence of the failure, each outputs its carrier, the nodes
110
,
111
, and
120
receive this carrier, whereas the nodes
101
,
112
, and
121
on upper-most streams in respective loops do not receive this carrier normally, because the carriers output from the nodes
100
,
110
, and
120
on lower-most streams in the respective loops collide on the common transmission line
15
. Thereafter, when the nodes (
101
,
112
,
121
) which did not receive this carrier, output responses including their node addresses, these responses also collide on the common transmission line
15
, and therefore, the responses cannot be received normally, either. As a consequence, the location of the failure cannot be detected/specified.
In some networks, when a failure occurs at a master node, an alternative master node is selected, whereby stop of operation of the whole network can be avoided. In such networks, it is required that the node which has detected occurrence of the failure decide whether or not the alternative master node should be selected depending upon whether or not the failure has occurred at the master node, respectively. Unless this decision is made, when a failure occurs and the alternative master node need not be selected, a node decides that the alternative master node should be selected even though this is unnecessary, and thereby operates as the alternative master node, which adversely affects operation of the network. On the other hand, when a failure occurs and the alternative master node should be selected, if it is decided that the alternative master node need not be selected even though this is necessary, the alternative master node will not be selected.
To make the above decision, it is necessary to specify the location of the failure. In the method disclosed in Japanese Published Patent Application No. Syo. 56-161742, the location of the failure cannot be specified in the network disclosed in the Japanese Published Patent Application No. Hei. 10-113459.
SUMMARY OF THE INVENTION
The present invention is directed to solving the above-described problem, and it is an object of the present invention to provide a network system, a method for specifying a location of a failure, and a method for recovering from the failure, in which occurrence of the failure is detected and the location of the failure is specified, and when a failure occurs at a master node, an alternative master node is automatically selected from slave nodes, whereby stop of operation of the whole network system due to the failure of the master node is avoided, using the network system in which at least one loop comprising plural loop-connected nodes and at least one loop comprising either a single node or plural loop-connected nodes are directly connected to a common transmission line shown in FIG.
13
.
Other objects and advantages of the invention will become apparent from the detailed descripti
Hattori Toshikazu
Ikeda Toshihisa
Mizuguchi Yuji
Moriguchi Ken-ichi
Sakai Takahisa
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Ton Dang
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