Data processing: structural design – modeling – simulation – and em – Emulation
Reexamination Certificate
1998-08-07
2001-03-06
Teska, Kevin J. (Department: 2123)
Data processing: structural design, modeling, simulation, and em
Emulation
C709S226000, C709S239000, C714S004110
Reexamination Certificate
active
06199033
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a network realized by LAN (Local Area Network) emulation, and more particularly to a LAN emulation server changing over method which allows continuous operation of a network in which LAN emulation servers are redundantly arranged and one of the LAN emulation servers acts as an operational LAN emulation server while the other one or ones of the LAN emulation servers act as a spare LAN emulation server or servers, when a failure occurs with the operational LAN emulation server, without manual changing over of the servers by a maintenance engineer.
2. Description of the Related Art
In a LAN emulation system, a failure of a LAN emulation server which performs address solution and broadcasting between communication terminals is a critical failure by which the entire system is disabled and the network is halted. Where a plurality of LAN emulation servers are disposed on a same network in order to prevent such system down, there is the possibility that the LAN emulation servers may be put into an operative condition simultaneously, resulting in disintegration of the network.
Meanwhile, where a dual construction is realized by a health check by a fixed bus between a plurality of LAN emulation servers arranged on a same network, determination of an operational one and a spare one of the servers must be determined in advance by a maintenance engineer.
For example, a server-client type network system disclosed in Japanese Patent Laid-Open Application No. Heisei 7-182297 includes a plurality of server units which communicate with each other to execute same information processing on the same network, and one of the server units which possesses a network operation right is determined as an operational server unit while the other is determined as a spare server unit. The spare server unit transmits and receives data to and from the operational server unit and establishes synchronism of transaction data to request the operational server unit for data of an operation condition of the same. Then, if an abnormal condition of the operational server unit is detected, then the spare server unit acquires the network operation right and succeeds processing being executed till then from the operational server unit.
However, where the conventional redundancy construction of LAN emulation servers described above is employed, if the plurality of LAN emulation servers which provide equivalent services to each other on the same network operate simultaneously, then there is the possibility that disintegration of the network may occur.
In order to eliminate the possibility described above, the server-client type network system described above must be constructed such that services must be provided only by the operational server unit, and if a failure occurs with the operational server unit, then a maintenance engineer must change over so that the spare server unit may thereafter act as an operational server unit instead.
Further, special means is required to allow communication of information regarding an operation condition of the operational server unit between the operational server unit which is supervised and the spare server unit which supervises.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a LAN emulation server changing over method by which, even if a plurality of LAN emulation servers on a network operate simultaneously, a spare one of the LAN emulation servers can supervise an operational one of the LAN emulation servers without requiring special means for communication of information regarding an operation condition of the operational LAN emulation server between the operational LAN emulation server and the spare LAN emulation server without causing disintegration of the network and, if a failure occurs with the operational LAN emulation server, changing over to the spare LAN emulation server can be performed immediately.
In order to attain the object described above, according to as aspect of the present invention, there is provided a LAN emulation server changing over method for a server-client type network system wherein a plurality of LAN emulation servers and a plurality of LAN emulation clients are connected to each other by a network, wherein a spare one of the LAN emulation servers subscribes as a LAN emulation client for an operational one of the LAN emulation servers and supervises a condition of the operational LAN emulation server, and, if an abnormal condition of the operational LAN emulation server is detected, then the spare LAN emulation server issues an operational/spare changing over request to the operational LAN emulation server and is changed over to an operational LAN emulation server whereas the LAN emulation server which has been the operational LAN emulation server is changed over to a spare LAN emulation server.
With the LAN emulation server changing over method, since the spare LAN emulation server can subscribe as a LAN emulation client for the operational LAN emulation server and supervise the condition of the operational LAN emulation server, special means for communicating data between the servers is not required. Further, since the condition of the operational LAN emulation server is supervised not periodically at certain time intervals but normally and incessantly, even if a failure occurs with the operational server, service can be automatically resumed immediately only after disconnection of a very short time without intervention of a maintenance engineer.
In the LAN emulation server changing over method, when operation of the network system is started, preferably it is automatically determined which one of the LAN emulation servers becomes an operational LAN emulation server and which one of the LAN emulation servers becomes a spare LAN emulation server. The determination of which one of the LAN emulation servers becomes an operational LAN emulation server and which one of the LAN emulation servers becomes a spare LAN emulation server may be performed by communicating peculiar values of the LAN emulation servers between the LAN emulation servers. Such determination eliminates an operation for setting operational/spare servers by a maintenance engineer.
In the LAN emulation server changing over method, when the operational LAN emulation server is changed over to a spare LAN emulation server, the operational LAN emulation server may release those LAN emulation clients which have been subscribed for the operational LAN emulation server till then, and the released LAN emulation clients may subscribe for the new operational LAN emulation server after the changing over.
According to another aspect of the present invention, there is provided a LAN emulation server changing over method for a server-client type network system wherein a plurality of LAN emulation servers and a plurality of LAN emulation clients are connected to each other by a network, wherein a spare one of the LAN emulation servers subscribes as a LAN emulation client for an operational one of the LAN emulation servers and supervises a condition of the operational LAN emulation server, and, if the spare LAN emulation server detects disconnection from the operational LAN emulation server and fails in a fixed number of retries, then the spare LAN emulation server determines that a failure has occurred with the operational LAN emulation server and begins to act as a temporary operational LAN emulation server and accept requests from the LAN emulation clients, and then if a fixed number of LAN emulation clients do not subscribe for the temporary operational LAN emulation server in a fixed time after the acceptance of requests is started, the temporary operational LAN emulation server determines that there still remains the possibility that the old operational LAN emulation server may still be acting as an operational LAN emulation server and itself issues a request for subscription as a LAN emulation client for the old operational LAN emulation server, whereafter, if the temporary operational LA
Choi Kyle J.
McGuireWoods LLP
NEC Corporation
Teska Kevin J.
LandOfFree
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