Electrical computers and digital processing systems: multicomput – Computer network managing – Computer network monitoring
Reexamination Certificate
2000-08-31
2004-10-12
Follansbee, John (Department: 2154)
Electrical computers and digital processing systems: multicomput
Computer network managing
Computer network monitoring
C714S004110
Reexamination Certificate
active
06804715
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a switch control apparatus used in switch control of a client/server system operating on a plurality of nodes which are mutually connected via a network, a switch control method, and a computer-readable recording medium in which is recorded a switch control program.
BACKGROUND OF THE INVENTION
Generally, a client/server system comprises at least two servers (main server and alternative server) having a series complex constitution, and a plurality of clients which are connected to the servers via a network. In such a client/server system, when a communications irregularity has been detected, the server providing the communications services to the clients is uniformly switched from the main server to the alternative server.
However, depending on the cause of the irregularity, the above switch control sometimes has the opposite effect of reducing the number of clients capable of receiving the communications services from the server. Consequently, there is a demand for an apparatus and a method to effectively solve this problem.
FIG. 7
is a block diagram showing the constitution of a conventional client/server system. In
FIG. 7
, nodes
10
,
20
and
30
are mutually connected via a communications path for data
40
(communications path for control
50
). A main server
11
and a client
12
operate in the node
10
. An alternative server
21
and a client
22
operate in the node
20
. A client
32
operates in the node
30
.
In the node
10
, the main server
11
supplies predetermined communications services to the clients
12
,
22
and
32
. The main server
11
functions as a present system server of the client/server system. The client
12
connects to the main server
11
and receives communications services therefrom during regular operation. When an irregularity occurs, the client
12
is able to switch from the main server
11
so as to receive communications services from the alternative server
21
.
A communications section
13
is inserted between the main server
11
and the client
12
and the communications path for data
40
, and controls communications between the main server
11
and the client
12
and the external nodes
20
and
30
in compliance with a predetermined communications protocol. A switch control section
14
controls the switching from the main server
11
to the alternative server
21
. A communications section
15
is inserted between the switch control section
14
and the communications path for control
50
, and controls communications between the switch control section
14
and the external nodes
20
and
30
in compliance with a predetermined communications protocol.
In the node
20
, the alternative server
21
realizes the same functions as the main server
11
, and provides the communications services instead of the main server
11
in the event of an irregularity. That is, the alternative server
21
functions as a standby server for the present server (the main server
11
). Thus the conventional client/server system uses an in-series complex constitution comprising the main server
11
and the alternative server
21
.
The client
22
receives communications services from the main server
11
during regular operation. When there is an irregularity, the client
22
is able to switch from the main server
11
so as to receive communications services from the alternative server
21
. A communications section
23
is inserted between the alternative server
21
and the client
22
and the communications path for data
40
, and controls communications between the alternative server
21
and the client
22
and the external nodes
10
and
30
in compliance with a predetermined communications protocol.
A switch control section
24
controls the switching from the main server
11
to the alternative server
21
. A communications section
25
is inserted between the switch control section
24
and the communications path for control
50
, and controls communications between the switch control section
24
and the external nodes
10
and
30
in compliance with a predetermined communications protocol.
In the node
30
, the client
32
receives communications services from the main server
11
during regular operation. When there is an irregularity, the client
32
is able to switch from the main server
11
so as to receive communications services from the alternative server
21
. A communications section
33
is inserted between the client
32
and the communications path for data
40
, and controls communications between the client
32
and the external nodes
10
and
20
in compliance with a predetermined communications protocol.
A switch control section
34
controls the switching from the main server
11
to the alternative server
21
. A communications section
35
is inserted between the switch control section
34
and the communications path for control
50
, and controls communications between the switch control section
34
and the external nodes
10
and
20
in compliance with a predetermined communications protocol.
In the constitution described above, the main server
11
provides communications services in accordance with requests from the client
12
in the node
10
, the client
22
in the node
20
and the client
32
in the node
30
. The main server
11
provides the communications services to the client
12
in the same node
10
. Furthermore, the main server
11
provides the communications services to the client
22
in the node
20
via the communications section
13
, the communications path for data
40
and the communications section
23
. Moreover, the main server
11
provides the communications services to the client
32
in the node
30
via the communications section
13
, the communications path for data
40
and the communications section
33
.
In addition to providing the communications services described above, the main server
11
checks the communications statuses (regular or irregular) of the clients
12
,
22
and
32
at fixed intervals. Specifically, the clients
12
,
22
and
32
each transmit a fixed-cycle communications packet to the main server
11
in a fixed cycle (e.g. every five seconds). This fixed-cycle communications packet comprises an address of the transmission destination main server
11
, an address of the transmission source (the address of the clients
12
,
22
and
32
) and dummy data.
The main server
11
receives the fixed-cycle communications packets and deems a check result of the communications status of each client to be regular. In the case where no fixed-cycle communications packet is received from the client even when a predetermined period (e.g. thirty seconds) has elapsed from the time when the previous fixed-cycle communications packet was received, the main server
11
deems the check result of communications status of that client to be irregular.
When the communications section
23
in the node
20
breaks down, the main server
11
does not receive a fixed-cycle communications packet from the client
22
. Therefore, the main server
11
deems the check result of the communications status of the client
22
to be irregular. In this case, the two clients
12
and
32
can receive the communications services from the main server
11
, but the client
22
cannot.
The main server
11
notifies the switch control section
14
that the irregularity has been detected. The switch control section
14
switches access destination of the client
12
in the node
10
from the main server
11
to the alternative server
21
. Furthermore, the switch control section
14
outputs a switch signal via the communications section
15
, the communications path for control
50
and the communications section
25
to the switch control section
24
in the node
20
, and outputs a switch signal via the communications section
15
, the communications path for control
50
and the communications section
35
to the switch control section
34
. As a consequence, the switch control sections
24
and
34
switch the access destination
Chujo Yoshihisa
Koseki Michihiko
Chang Jung-won
Follansbee John
Fujitsu Limited
Staas & Halsey , LLP
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