Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
1999-01-14
2002-06-25
Beausoleil, Robert (Department: 2184)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
Reexamination Certificate
active
06412077
ABSTRACT:
COPYRIGHT AUTHORIZATION
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by any one of the patent disclosures, as it appears in the U.S. Patent & Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
FIELD OF THE INVENTION
The present invention generally relates to distributed computing systems, and more specifically relates to performing a disconnect policy in a distributed computing system.
BACKGROUND OF THE INVENTION
A distributed computing system is a system having resources that are physically distributed among different locations. In general, the resources that make up a distributed computing system include information and data, which may be in many forms and formats, and various hardware and software components that are used to access, manage, manipulate and process the information and data.
One approach to implementing a distributed computing system is through the use of a network system. In general, a network system is a collection of computers and other peripheral devices that are connected in a manner that enables them to communicate with each other. The computers and other peripheral devices typically include software and hardware components that allow information and data to be distributed throughout the network.
Many network systems provide mechanisms that allow them to be remotely accessed. By allowing remote access, individuals can connect to the network system to access resources and obtain information while being located at a remote site.
A popular method of providing remote access to a network is through the use of a dial-in network access server (NAS) that controls access to the network. For example, model AS5300, commercially available from Cisco Systems Inc., can be used to provide dial-in access to a network system. Individuals can access the network system by dialing into the network access server from a Remote Node to establish a connection. In this document, the term Remote Node refers to any client device, such as a personal computer (PC) or router, that can be used to dial in and establish a connection with a network access server. A client/server relationship exists between the Remote Node and the network access server.
For example, many home and office computers are equipped or have access to a modem that can be used to establish a dial-in connection with a NAS. These dial-in connections may be made using one of the Internet's standard dial-in protocols, either the Point-to-Point Protocol (PPP) or the Serial Line Internet Protocol (SLIP). To establish a connection with a particular NAS, a user interacts with the computer to cause a modem to dial into the particular NAS. As part of the dial in process, identification information, such as a user name and password, is provided to the NAS. The NAS validates the login information, and if it is valid, the NAS establishes a “session” for the particular user. In this context, a session is a specific connection that has been established for a particular user between a Remote Node and a server and which provides access to a network system. Thus, once a session is established, the user can access resources and obtain information that is associated with the network system.
In general, it is important to be able to control and monitor the users or group of users that are able to login and establish a session with an NAS. For example, Internet Service Providers (ISPs) allow customers to log in and establish sessions with an NAS in order to obtain access to resources that are available on the Internet. Several ISPs and “Online Services,” such as America Online® and CompuServe®, also provide their customers with access to proprietary information (such as proprietary databases and forums) and other online services that are available through their NAS connections. For providing access to these resources, the ISPs and Online Services charge their customers a connection fee that may be on an hourly connection or monthly flat lee basis. Thus because their revenue is dependent on the fees that are paid by their customers, the ISPs and Online Services need to monitor and control the users or group of users who are able to log in and establish a session with one of their NASs.
To reduce loads and better serve their customers, the ISPs and Online Services may provide a large number of NASs to which customers can dial in to establish a session . In addition, because their customers may not be confined to particular region, many ISPs and Online Services have distributed their NASs throughout the world. A benefit of distributing the NASs is that a significant number of customers are able dial in and establish a session by a local call. Thus, the customers are not required to make long distance calls to establish a session with a NAS, nor are the ISPs and Online Services required to provide an “800” number in order to reduce their customer's connection costs.
However, a drawback of providing multiple NASs for connecting to a network is that it can be difficult to control actual the number of sessions that are to be allowed for a particular user or group of users. One method of controlling the number of sessions that a particular user or group of users can establish is by maintaining a global count as to the total number of sessions that are currently active for a particular user or group of users. For example, by designating a particular NAS as the Central Authenticator, a global count of the total number of sessions that are currently established for a particular user or group of users can be maintained. Thus, before a NAS can establish a session for a particular user or group of users, it must first communicate with the Central Authenticator to determine whether the total number of allocated sessions have already been established for the particular user or group of users. If the Central Authenticator determines that the total number of allocated sessions have already been established for the particular user or group of users, then the connection request is denied. Alternatively, if Central Authenticator determines that the total number of allocated sessions have not yet been established, then the connection request is granted.
However, always having to communicate with a Central Authenticator to determine whether a connection request should be granted has a drawback, namely that if the Central Authenticator crashes or communication to the Central Authenticator is lost, a user or group of users may be denied a session even though the total number of allocated sessions have not yet been established (“under-subscription”).
For example, a company “A”, which has employees located in five (“5”) cities (San Diego, Los Angeles, San Jose, San Francisco and Irvine) may have a total of one hundred (“100”) sessions allocated for its employees, but may have only twenty-five (“25”sessions that are currently active. By locating a NAS in each of the five cities, the employees of company “A” can dial into a local NAS to request a session. Upon receiving the request, the NAS may communicate with the Central Authenticator to verify that a session can be established for the employee. However, if the Central Authenticator has crashed or the communication link between the local NAS and the Central Authenticator has failed, there is no way to determine that a session should be established for the particular employee. Thus, the session request cannot be granted and the employee will be denied access to the network, even though the total number of sessions that are active for the employees of company “A” (“25”) is less than the total number of allocated sessions (“100”) (“under-subscription”). In this context, a communication link failure includes but is not limited to any type of hardware or software failure that impedes or obstructs two components from communicating with one another.
One approach to avoiding under-subscription is to implement a “hot” backup system
Cates David
Knight John
Roden Thomas Anthony
Beausoleil Robert
Bonzo Bryce P.
Cisco Technology Inc.
Hickman Palermo & Truong & Becker LLP
Palermo Christopher J.
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