Electrical computers and digital processing systems: multicomput – Remote data accessing – Accessing a remote server
Reexamination Certificate
1998-10-26
2001-04-24
Follansbee, John A. (Department: 2154)
Electrical computers and digital processing systems: multicomput
Remote data accessing
Accessing a remote server
C709S203000, C709S227000, C709S241000, C710S010000
Reexamination Certificate
active
06223217
ABSTRACT:
COPYRIGHT NOTIFICATION
Portions of this patent application contain materials that are subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document, or the patent disclosure, as it appears in the Patent and Trademark Office. All other rights are expressly reserved.
FIELD OF THE INVENTION
This invention relates generally to improvements in distributed computer networks and, more specifically, to operating system software for efficiently implementing client-server systems in distributed service networks.
BACKGROUND OF THE INVENTION
Computer hardware is becoming increasingly distributed and remote, resulting in networks of computers for solving problems in concert rather than as stand-alone systems. Although such distributed “services” networks generally facilitate problem-solving, they also increase the need for flexibility and functionality in software programs operating on the computers.
An example of a distributed services computer network is a “client-server” system
100
shown in FIG.
1
. The system
100
comprises a collection of client nodes
102
, e.g., workstations or personal computers, that communicate over a network
104
with various server nodes
106
. The servers are typically computers having hardware and software elements that provide a sophisticated set of services, or operations, for use by the client nodes
102
to increase the efficiency of their own operations.
Several types of networks, including local area networks (LANs), may be employed in the client-server system
100
. A LAN is a limited area network that typically consists of a transmission medium, such as a coaxial cable or twisted pair, for interconnecting the client and server nodes. Each node is connected to the transmission medium at an address which uniquely identifies the node and which is used to route data from one node to another.
Nodes coupled to the network typically communicate by exchanging discrete “packets” of data according to predefined “protocols”. In this context a protocol consists of a set of rules defining how the nodes interact with each other. For example, communication in the client-server system
100
typically takes the form of packet exchanges, wherein the clients
102
send requests to the servers
106
, which perform their services and communicate results back to the clients.
In order to reduce design complexity, most networks are organized as a series of hardware and software levels or “layers” within each node. These layers interact to format data for transfer between nodes that are communicating over the network. Specifically, predetermined services are performed on the data as it passes through each layer and the layers communicate with each other by means of the predefined protocols. This layered design permits each layer to offer selected services to other layers using a standardized interface that shields those layers from the details of actual implementation of the services.
In an attempt to standardize network architectures, i.e., the sets of layers and protocols used within a network, a generalized model has been proposed by the International Standards Organization (ISO). The model, called the open systems interconnection (OSI) reference model, addresses the interconnection of systems that are “open” for communication with other systems. The proposed OSI model has seven layers which are termed, in ascending interfacing order, the “physical”, “data link”, “network”, “transport”, “session”, “presentation” and “application” layers. These layers are arranged to form a protocol “stack” in each node of the network.
FIG. 2
illustrates a block schematic diagram of prior art protocol stacks
225
and
275
used to transmit data between a client node
200
and a server node
250
, respectively. The protocol stacks are structured according to the international standards organization OSI seven-layer model, which also standardizes the functions of their constituent layers. Accordingly, only the protocol stack
225
of the client node will be described.
Broadly stated, the physical layer
214
of the OSI model transmits a raw data bit stream over a communication channel
220
, while the data link layer
212
manipulates the bit stream and transforms it into a data stream that appears free of transmission errors. This latter task is accomplished by dividing the transmitted data into data frames and transmitting the frames sequentially, accompanied with error correcting mechanisms for detecting or correcting errors. The network layer
210
routes data packets from a source node to a destination node by selecting one of many alternative paths through the physical network. The transport layer
208
accepts the data stream from the session layer
206
, apportions it into smaller units (if necessary), passes the smaller units to the network layer
212
, and provides appropriate mechanisms to ensure that all the units arrive correctly at the destination.
The session layer
206
establishes “sessions”, i.e., connections, between software processes on the source and destination nodes, and transfers data over those connections in an orderly fashion. That is, a session not only allows ordinary data transport between the nodes, but it also provides enhanced services in some applications, such as dialogue control. The presentation layer
204
performs frequently-requested functions relating to the presentation of transmitted data, including encoding of data into standard formats, while the application layer
202
contains a variety of protocols that are commonly needed by programs executing on the nodes, such as remote file access.
As can be seen in
FIG. 2
, the protocol stacks
225
and
275
are physically connected through the communications channel
220
at the physical layers
214
and
264
. Thus, data transmission over a client-server network consists of generating data messages in the application layer
202
of the client node
200
and passing the data messages down through the protocol stack
225
, where they are formatted for delivery onto the channel
220
as bits of packets. Those packet bits are transmitted to the protocol stack
275
of the server
250
, where they are passed up that stack to the application layer
252
. The generation and formation of data are performed by software programs executing on the nodes and, in some cases, hardware present on the nodes. The software programs may be generally categorized into two broad classes: application programs and operating systems. Operating systems are usually specific to a type of computer and consist of a collection of a utility procedures that enable the computer to perform basic operations, such as storing and retrieving information on primary and secondary storage devices, displaying information on an associated video display and, in some cases, performing network operations.
By itself, the operating system generally provides only very basic functions and must be accompanied by an “application” program. The application program interacts with the operating system to provide much higher level functionality and a direct interface with a user of the node. During interactions with the operating system, the application program typically invokes the utility procedures by issuing a series of parameter requests, via standard local procedure calls, to the operating system which then performs the request in accordance with the parameters. For example, the application program may “call” the operating system to store particular data on a computer disk memory or forward the data over the network.
As noted, a significant function of each layer in the OSI model is to provide services to the other layers. Two types of services offered by the layers are “connection-oriented” and “connectionless” network services. In a connection-oriented service, a source node establishes a connection with a destination node and, after sending a message, terminates the connection. The overhead associated with establishing the connection may be unattractive for nodes requiring e
Follansbee John A.
Kudirka & Jobse LLP
Object Technology Licensing Corporation
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