CH 08 Understanding Client Server Systems_Ch08

8/12/2019 CH 08 Understanding Client Server Systems_Ch08

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Client/Server Computing: DBMS concept andarchitecture, Single system image, Client

Server architecture, mainframe-centric client

server computing, downsizing and client

server computing, preserving mainframe

applications investment through porting,

client server development tools, advantages

of client server computing.


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Peer-peer network

computer network in which eachcomputer in the network can act as

a client or server for the othercomputers in the network, allowingshared access to files and

peripherals without the need for acentral server


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Peer-peer network


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Dis-advantages

No central server

No centralization

Lacking management

Back up and recovery possibility

Up gradation and scalability

Accessibility and security


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Peer-peer system vs. client/server


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Client/server design- classical model


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Forces that drive the Client/ServerThe general forces that drive the move toclient/server computing are:

The changing business environment. The growing need for enterprise data access. The demand for end user productivity gains

based on the efficient use for data resources. Technological advances that have made

client/server computing practical. Growing cost/performance advantages of PC-

based platforms.


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Client/Server ArchitectureThe client/Server architecture is based onhardware and software components that

interacts to form a system. This system includesthree main components:

ClientsServersCommunication middleware


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Client/Server Architecture - client

The client is any computer process thatrequests services from the server. Theclient is also known as the front-end-application, reflecting the fact that theend user usually interacts with the

client process.


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Client/Server Architecture - server

The server is any computer processproviding services to the clients. Theserver is also known as the back-endapplication, reflecting the fact that theserver process provides the background

services for the client process.


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Communication middleware:It is any computer process(es) through whichclients and servers communicate. The

communication middleware, also known asmiddleware or the communications layers, ismade up of several layers of software that aidthe transmission of data and controlinformation between clients and servers.


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CLIENT SERVER ARCHITECTURE

Distributed Processing Environment Distributed Database Environment Comprehensive Communications Networks Open Systems for information sharing Friendly User Interfaces Standardized communications protocols Shared responsibility


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CLIENT SERVER ARCHITECTURE

Client Processes request services Server Processes provide services Client and server processes execute on

different systems Clients and servers can negotiate the terms

and conditions of service


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Single System Image To implement and operate a modern

telecommunications network that creates a

seamless utility for all telecommunication

applications from desktop to desktop

Definition: In distributed computing, a single

system image (SSI) cluster is a cluster of

machines that appears to be one single system


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Single System Image Within the single system image environment, a

business system user is totally unaware ofwhere data is stored, how client and server

processors work, and what networking is

involved in gaining connectivity. How is this transparency accomplished?


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Single System Image Every application that the user accesses provides a

common look and feel. Help is provided in the same way

by every application. Errors are presented and resolved inthe same way. Each user has access to all services for whichhe or she has a need and a right to access

The security layer is invisible to the authorized andimpenetrable to the unauthorized

Navigation from function to function and application toapplication is provided in the same way in every system


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Single System Image client/server computing

Single system image is best implemented through

the client/server model

Client/server computing is an environment that

satisfies the business need by appropriately

allocating the application processing between the

client and server processors Communication mechanism: IPC, InterProcess

Communication


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Information Sharing approaches:Three approaches to organizational information

sharing:

Mainframe Centric:

PC Server-Centric:

Client Server:


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Mainframe-Centric: Use terminal emulators or hardwired terminals.

Non GUI proprietary interface.

Asynchronous (all cursor positions and key

positions are transmitted to and from the

mainframe).

Tight administrative control.


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Mainframe-CentricClient/Server Computing Uses the presentation capabilities of the

workstation to front-end existing applications

The data is displayed or entered through the use ofpull-down lists, scrollable fields, check boxes, andbuttons

The user interface is easy to use, and information ispresented more clearly


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PC-Server-Centric: PCs share common applications.

PCs share data (files).

PCs share resources (printer, etc.).

Each application presents its own user interface.

Commands and queries processed by PC.

Downloading of files (high volume network traffic).


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Client Server: Desktop intelligence.

Client responsible for User Interface.

Better sharing of server resources.

Optimal network utilization.

Separation of communication and operatingsystem processes from the user (easy maintenance).


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Downsizing & client/server computing

Benefits of rightsizing are reduction in cost and/or

increased functionality, performance, and

flexibility in the applications of the enterprise

Significant cost savings usually are obtained from

a resulting reduction in employee, hardware,

software, and maintenance expenses


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Downsizing & client/server computing

Rightsizing and downsizing are strategies used

with the client/server model to take advantage of

the lower cost of workstation technology

Rightsizing and upsizing involve the addition of

more diverse or more powerful computing

resources to an enterprise computing environment.


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Advantages of Client/Server

Computing

Enhanced data sharing

Integrated services

Sharing resources among diverse platforms

Data interchangeability and interoperability

Masked physical data access

Location independence of data and processing

Centralized management


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There are some major problems with this approach:

Mainframe system are very inflexible.

Centralized DP department was unable to keep up

with the demand for new applications.

high cost of purchase, maintenance and support.

CH 08 Understanding Client Server Systems_Ch08

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