Electrical computers and digital processing systems: multicomput – Distributed data processing – Client/server
Reexamination Certificate
1997-07-09
2001-01-09
Lim, Krisna (Department: 2758)
Electrical computers and digital processing systems: multicomput
Distributed data processing
Client/server
C709S201000, C709S238000, C709S245000, C711S202000, C711S203000, C714S004110, C370S409000
Reexamination Certificate
active
06173312
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high reliability network system for improving reliability of communications performed among a plurality of server and client computers connected in a network. In particular, the present invention relates to a technology which can effectively be applied to a high reliability network system to realize transfer of server function, backup and load dispersion, etc. without suspending the operations in the network.
BACKGROUND OF THE INVENTION
In conventional computer systems, a plurality of terminals are generally connected via a network around a host computer. Thereby, the host computer can realize concentrated processes. In such a conventional system, a circuit switching network and packet switching network according to a standard protocol X.25 has been introduced.
Since the reliability of the circuit switching was left in hands of the line provider, in order to have backup of the server computers, it was necessary to previously make registration of a calling destination in the event of a fault to a line control apparatus.
Moreover, the backup system according to X.25 is realized on the basis of the concept of transfer of terminated calls as can be seen in X.25 of CCITT (Consultative Committee for International Telephony and Telegraphy). In the case of transfer of terminated calls, a list of the transfer destinations to be used for transfer when the termination side is defective, or when there is a busy condition, is previously provided at the time of extending a virtual circuit depending on X.25. Thereby, transfer is attempted in the sequence of the list until the virtual circuit is normally extended according to the list of such transfer destination and communication can be realized.
On the other hand, in the current trend of down-sizing, computer systems have gradually shifted from a system for executing centralized processes with a large size computer to a distribution type server-client system consisting of a server computer formed from a work station, or the like, and a client computer mainly formed from a personal computer, or the like.
Moreover, as the connectivity of a network is assured with the same protocol not only in the LAN (Local Area Network) but also in WAN (Wide Area Network) by means of an IP (Internet Protocol) based network such as the internet, a large scale server-client system utilizing the same protocol network explained above can be established. Also, recently, portable type computers are frequently connected to such a server-client system for the purpose of communication and various discussions are now being made for IP for mobile communication which is used for moving the portable type computer in order to connect it to different networks.
FIG. 13
illustrates the structure of a network utilizing an IP for mobile communication of the related art. In
FIG. 13
,
1300
,
1310
and
1320
designate LANs;
1301
,
1311
and
1321
designate routers;
1302
,
1303
,
1304
and
1305
designate clients; and
1312
designates the client for mobile communication. The addresses are assigned in the network utilizing the IP for mobile communication of the related art. When the client
1312
for mobile communication is moved to LAN
1320
from LAN
1310
, and the client for the mobile communication
1312
has an identification address corresponding to the existing IP address and a virtual address which is set virtually in the network of the transfer destination.
In the existing network system, regarding the address of the client
1312
for mobile communication, the identification address and virtual address are both indicated as “b.a” when the client is connected to LAN
1310
and the address “b.a” is used for communication between the client
1312
for mobile communication and clients
1302
to
1305
. When the client
1312
for mobile communication is moved and connected to LAN
1320
, the address which is not used in LAN
1320
, for example, “c.a” can be set as the virtual address. When a packet for address “b.a” is transmitted from the clients
1302
to
1305
, the routers
1301
,
1311
and
1321
transmit the packet to the client
1312
for mobile communication moved to LAN
1320
by transferring the packet to the address “b.a” to the address “c.a”. Thus, when client
1312
for mobile communication is moved to a different LAN segment, communication can be made between the client
1312
for mobile communication and the clients
1302
to
1305
without changing the setting of the IP address of the client
1312
for mobile communication in the side of the clients
1302
to
1305
.
On the other hand, in a large scale server-client system structured as explained above, a plurality of server computers have usually been duplicated to provide against the faults occurring in the server computers, by selectively using two adjacent server computers as the working or backup server computers. The working server and backup server explained above have been connected with an exclusive bus or network, but a plurality of server computers for working server and backup server must be located at the position of the same LAN segment. In addition, according to a certain method, the working server is switched to the backup server in the distant area by allocating the backup server in the distant area. But in this method, the transfer of terminated calls or the method similar to such transfer of terminated calls has been employed.
SUMMARY OF THE INVENTION
The inventors of the present invention have found the following problems as a result of reviewing such related art. First, backup or switching for the server computer connected by WAN can be realized through circuit switching or packet switching, but software using IP is now used according to a standard due to the influence of internet in the field of the WAN and reconsideration must be done in the basis of IP even for the system for executing backup and switching of the server computer. Second, in the existing network system, a list of transfer destinations for the fault is controlled statically but modification of structure of network or change of address often occur in response to the increase in the number of devices connected to the network. Moreover, contents of the list of transfer destinations must be updated for each change of address in the static management of the transfer destination list, resulting in the problem that the packets to the working server are not correctly transferred to the backup server if updating of the transfer destination list is delayed when the working server fails and switching to the backup server is executed.
In addition, in the network of the related art, the transfer destination list can immediately be updated when a fault occurs in the working server and the working server can be switched to the backup server through the transfer of terminated call. However, the address of the server computer accessed is often defined statically in the client computer and it has also been required to change the address of the server computer as the transmission destination in the side of client computer at the time of transmitting or receiving the packets between the backup server and client computer.
It is therefore an object of the present invention to provide a technique for switching from a working server to a backup server without changing the setting on the client computer.
It is another object of the present invention to provide a technique for switching between the working and backup servers connected on different networks without changing the setting on the client computer.
It is still another object of the present invention to provide a technique for selecting the optimum path to the backup server from the client computer when the working server is switched to the backup server.
It is yet another object of the present invention to provide a technique for switching the server to a backup server having no server switching function.
In order to realize the above-mentioned objects of the present invention, some aspects of the invention are summa
Atarashi Yoshifumi
Hayashi Kenji
Ikeda Naoya
Yamaguchi Shoichiro
Barot Bharat
Hitachi , Ltd.
Lim Krisna
Mattingly Stanger & Malur, P.C.
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