Electrical computers and digital processing systems: multicomput – Multicomputer data transferring via shared memory – Partitioned shared memory
Reexamination Certificate
1998-11-19
2002-01-01
Maung, Zarni (Department: 2154)
Electrical computers and digital processing systems: multicomput
Multicomputer data transferring via shared memory
Partitioned shared memory
C709S227000, C709S241000
Reexamination Certificate
active
06336135
ABSTRACT:
FIELD OF INVENTION
The present invention relates to linking together data communications and/or data processing resources in a network, and in particular to providing links between different communications environments.
BACKGROUND OF THE INVENTION
A ‘network’ of computers can be any number of computers that are able to exchange information with one another. The computers may be arranged in any configuration and may be located in the same room or in different countries, so long as there is some way to connect them together (for example, by telephone lines or other communication systems) so they can exchange information. Just as computers may be connected together to make up a network, networks may also be connected together through tools known as bridges and gateways. These tools allow a computer in one network to exchange information with a computer in another network. The Internet is a network of networks having no single owner or controller and including large and small, public and private networks, and in which any connected computer running Internet Protocol software is, subject to security controls, capable of exchanging information with any other computer which is also connected to the Internet. This composite collection of networks which have agreed to connect to one another relies on no single transmission medium (for example, bidirectional communication can occur via satellite links, fiberoptic trunk lines, telephone lines, cable TV wires and local radio links).
The World Wide Web (WWW) Internet service is a wide area information retrieval facility which provides access to an enormous quantity of network-accessible information and which can provide low cost communications between Internet-connected computers. Information about the World Wide Web can be found in “Spinning the Web” by Andrew Ford (International Thomson Publishing, London 1995) and “The World Wide Web Unleashed” by John December and Neil Randall (SAMS Publishing, Indianapolis 1994). Use of the WWW is growing at an explosive rate because of its combination of flexibility, portability and ease-of-use, coupled with interactive multimedia presentation capabilities. The WWW allows any computer connected to the Internet and having the appropriate software and hardware configuration to retrieve any document that has been made available anywhere on the Internet. The retrievable documents on the WWW include ‘HyperMedia’ documents—i.e. documents which may be text documents or other forms of media such as sounds and images and which have links (‘hyperlinks’) to other documents. The format of text documents on the WWW is a standard format in HTML (HyperText Markup Language), such that a document created on one operating system and hardware platform can be read by a user on any other platform that has a Web Browser (see below). Images may be stored in separate graphics files, for example in standard GIF or JPEG format, and referenced in the HTML text such that the user is prompted to retrieve the specified image files as well as the HTML text.
Users access this information using a ‘Web Browser’, or ‘Web client’, which is software installed on the user's computer and having facilities for serving or retrieving documents from a Web Server via the Internet. Currently available Web Browsers include WebExplorer from IBM Corporation and Mosaic from NCSA. Such Browsers include directories and search tools and understand HTML and other WWW standard formats and can display or output files correctly in these formats. The user interface of these Web Browsers is a graphical ‘point-and-click’ interface (i.e. items can be selected by moving a cursor across a graphical display and then pressing a mouse button). The WWW is structured as pages or files which each have a particular Universal Resource Locator (or URL). The URL denotes both the server machine and the particular file or page on that machine. The user can either specify a particular URL or jump from one URL to an associated URL by means of the ‘hyperlinks’—that is, a word or symbol on a page can be associated with another URL which is selectable, for example by clicking a mouse at the relevant location, to cause the Browser to retrieve and display the relevant page. There may be many pages resident on a single server, and associated hyperlinked pages may be located on different servers. If a URL begins “http:” then this indicates that the file contains hyperlinks.
When a user selects a URL for a page on a Web server system using his Web Browser, a one-shot request is sent to the relevant server which performs an action specific to that page. In many cases the server responds to the request by retrieving the requested page from a database of stored pages and transmitting the HTML page back over the Internet to the WWW client for display to the user. This is performed within the scope of a single end-to-end synchronous communication session. That is, the Browser sends its request and then waits for a response before proceeding with any further processing or initiating other requests. The Browser is said to be ‘blocked’ or ‘suspended’ while it waits for the requested response. In some cases the Browser's request will lead to the server launching an application to generate the HTML, but again the one-shot request from the Browser requires a response within the scope of the present synchronous communication session since the Browser does not provide for concurrent communication sessions and no application state information is maintained between requests. A failure to access a page requested by a Browser can be signalled back to the user by means of an error message displayed on the user's terminal, but if the server is merely slow to respond then the Browser remains suspended for an indefinite period. In practice, a user may abandon the communication attempt if the delay is unacceptable to them. There is no facility within Web Browsers for automatic retry of a request.
Modern enterprises require facilities for communication with other departments within the enterprise and with associated enterprises such as customers or suppliers, who may be in a different country. The WWW Internet service can provide a partial answer to such a requirement, providing a cost effective communication medium for inter-company communications, but the WWW Internet service's one-shot request-response communication model and the lack of provision for parallel requests from a Browser can represent severe limitations if requested information is not available within an acceptable time period. It is often unacceptable for a sender system to be suspended indefinitely and it is unacceptable for the success of business-critical applications to be dependent on whether a server application responds to a request in time. The WWW Internet service does not provide facilities for assured delivery of messages which is a requirement of many business critical applications (that is, the application needs to know that a message it has sent will not be lost on its way to the target destination, and that it will only be sent once). Also, business applications may involve a conversation taking up many request-response pairs and the lack of any context information being carried over between Web Browser requests means that there is no facility for relating together requests which are part of the same business application.
An alternative communication model to the synchronous, time-dependent ‘request and await response’ model is asynchronous messaging. A program which sends a message to a receiver program need not be blocked to await a reply from the receiver and so can continue executing, and the sender and receiver are not synchronised (serialised) with one another. Asynchronous inter-program messaging typically uses message queues as intermediate storage facilities into which messages are placed when sent from a first program and from which they can be retrieved by a receiver program when it is ready. There is no dedicated logical connection between the programs. After placing a message in a queue, th
Niblett Peter David
Randell Karen Louise
Caldwell Andrew
Herndon Jerry W.
Maung Zarni
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