Network bandwidth and object obsolescence sensitive...

Details Network bandwidth and object obsolescence sensitive... Network bandwidth and object obsolescence sensitive...

1997-11-26

2001-09-18

Luu, Le Hien (Department: 2152)

Electrical computers and digital processing systems: multicomput

Computer-to-computer protocol implementing

Computer-to-computer data transfer regulating

C709S203000, C709S241000, C709S217000, C707S793000, C707S793000

Reexamination Certificate

active

06292835

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an improved data processing system, and more specifically, to the dissemination (or broadcasting, or replication) of information from servers to their networked clients. In particular, a method and apparatus are disclosed for transferring data while optimizing currency of information under bandwidth constraint by taking into account available bandwidth.
GLOSSARY OF TERMS
While dictionary meanings are intended for certain terms used here, the following glossary of terms may be useful.
Internet: The network of networks and gateways that use the TCP/IP suite of protocols.
Channel: A group of relevant objects (see object) published by a server (see server) and subscribed by many clients (see client).
Client: A computer which issues commands to the server which performs the task associated with the command.
Object: One or a group of multimedia objects. Each multimedia object can be a text document, a binary file, an image, a video/audio clip, etc.
Server: Any computer that performs a task at the command of another computer is a server. A web server or Lotus Notes server typically supports one or more clients.
Web Browser: A software system running on the clients that provides the interface for users to select desired objects, a mechanism to request and retrieve the desired objects from the servers, and the interface to display the retrieved objects to the users.
World Wide Web (WWW or Web): The Internet's application that lets people seeking information on the Internet switch from server to server and database to database by clicking on highlighted words or phrases of interest (hyperlinks). An Internet WWW server supports clients and provides information. The Web can be considered as the Internet with all of the resources addressed as URLs and which uses HTML to display the information corresponding to URLs and provide a point-and-click interface to other URLs.
BACKGROUND OF THE INVENTION
An essential function in many of today's data processing systems has been the dissemination of information from servers to clients via a computer network. In one class of such systems, information is continually sent from servers to a large number of clients. One example of such a system is object pushing on the World Wide Web (WWW or web). Another example is data replication in a distributed database system such as Lotus Notes.
Traditionally, object retrieval on the web is based on pull technology. In this approach, a web user retrieves a web object by clicking an icon or a hyperlink through a web browser, which then establishes a network connection to a web content provider and proceeds to download and display the requested object. If the requested information is retrieved through a slow network, a noticeable latency may occur at the user end. To avoid the long wait for pulling the requested documents, an alternative is to have the server push the information to the users based on pre-specified user preferences or profiles as soon as relevant information becomes available. The users therefore receive the requested information without having to wait. Currently, most push technologies are based on background pull where a software application, executing on behalf of the user, periodically pulls the requested objects in the background.
In a distributed database system such as Lotus Notes, server databases are used to store the complete original data, whereas each client is database can maintain a duplicate subset of the server data. It is important that the contents in the client databases reflect their corresponding subsets in the server databases as accurately as possible. To achieve this, a client database periodically invokes a data replication process which connects to the server and retrieves any new information from the server databases.
In both applications (object pushing in WWW and data replication in distributed systems), as well as other systems that require data be continually sent from the servers to the clients, an important consideration is when and how often the client contents are updated. Ideally, one would like the client contents to be updated whenever their corresponding server data changes. However, this is impractical as frequent updates from a large number of clients may demand a very high network bandwidth capability not available in most organizations that run the relevant systems such as object pushing on web or data replication in distributed databases. In practice, most of these systems adopt a default periodical update mechanism in which each client sets beforehand fixed update schedules, one for each server it subscribed to. In addition, many of these systems also provide a demand-driven update mechanism such that a client can immediately request an update from a certain server if an urgent need arises.
While the pure demand-driven update scheme can be too costly in terms of bandwidth usage, the regularly scheduled updates provide flexibility in preserving bandwidth. However, it may be important for clients to set an appropriate update frequency for each server to which they are subscribed. If the frequency is too high, network bandwidth may be overflowed with the update traffic; if the frequency is too low, the information maintained by the clients may become too outdated. In the case of object push in WWW, it has been found that users tend to inadequately specify their preferences for updates with high frequencies such that many corporate gateways are often flooded with push traffic.
To alleviate this push overflow problem, push product vendors have developed proprietary proxy server software. In general, these proxy servers cache recently retrieved push objects. For each push request, these proxy servers desirably search their cache for the requested objects. If an object is found in the cache, that object is sent back to the user who made the request. If an object is not found in cache, or if the found object is considered too old, these proxy servers may relay a background pull to the original content provider to retrieve the requested object via corporate gateways. This approach can improve the gateway traffic because some client requests will involve only the retrieval of information from the proxy server's cache, and the number of cross-gateway update requests will decrease as a result.
In this proxy approach, the proxy updates have replaced the client updates in direct contact with the servers, and it is the proxy's responsibility to keep the contents stored in their caches up to date in order to reflect the new changes from the servers. When more corporate users are subscribing to the increasing number of channels that publish push objects (as is the current trend), the proxy-based update traffic can still flood the gateways if it does not take into consideration the gateway traffic condition. The same analogy can also be applied to the problem of periodical data replication beyond local gateways in a distributed database system.
Another problem with the current scheduled update approach is that once a schedule is set, the updates follow the same frequency pattern until a new schedule is manually set at a later time. In many occasions, the interest in accessing the latest information from a channel changes over time and the current approach cannot adapt to these dynamic changes. For example, a sudden stock plunge could generate a tremendous number of instant interest within a finance-related organization. Many opportunities may be lost if its proxy server is not adaptive enough to provide more updated information than previously scheduled.
SUMMARY OF THE INVENTION
In a network in which data is transferred from servers to clients through a proxy, the update frequency with which data is cached by the proxy is determined. An indication of available bandwidth for performing updates of data cached by the proxy is received. When to update data cached by the proxy is then calculated based upon the indication of available bandwidth.


REFERENCES:
patent: 5403639 (1995-04-01), Belsan et al.

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