unit – i client / server architecture. unit structure evolution of client/server architecture ...
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Unit – I
CLIENT / SERVER
ARCHITECTURE
Unit Structure
Evolution of Client/Server ArchitectureClient/Server ModelCharacteristics of Client/Server ModelClient/Server Architecture in the WebTypes of ServersTypes of Client/Server Models Advantages & Disadvantages of
Client/Server Model
Evolution of Client/Server Architecture
Mainframes Dumb Terminals All processing/data storage on mainframe computer Large number of users Expensive
Personal Computers Single User system Word Processing, Data Analysis using Spreadsheet Multimedia Applications & Games
Evolution of Client/Server Architecture
Clients & Server on different computer systems Local Area Network for Server and Client
connectivity Multiple Users Distributed computation, analysis, and presentation
between PCs Evolved during 1980s Heterogeneous hardware and software Provides greater usability, flexibility, scalability and
interoperability
CLIENT / SERVER MODEL
Model or architecture describes the relationship between two computer programs – Client & Server
Client is the requester that makes a service request
Server fulfills the request or services the request
Multiple client programs share the services of a common server program
CLIENT / SERVER MODEL
Servers typically contain data files & applications accessed by multiple clients
Client & Server share the processing loadClient / Server can be on same computer
system or on different computer systemsClient/Server model - a convenient way to
interconnect programs distributed across different locations
CLIENT / SERVER MODEL
Client initiates request
Server services request
SERVER CLIENT
CLIENT / SERVER MODEL
Server can range from PCs to mainframesStandard Server hardware
Support for large amount of RAM Fast input and output Fast network cards Ability to support multiple processors Support for fault tolerance
Characteristics of Client/Server Model
Asymmetrical protocolsEncapsulation of servicesLocation transparencyMessage-based exchangesModular, Extensible designPlatform IndependenceScalabilitySeparation of Client/Server Functionality Shared resources
Characteristics of Client/Server Model
Benefits Provided by Server Optimization Centralization Data Integity Security Back-up
Function of Client / Server Client
Initiates requests Waits for and receives replies Can connect to several servers at the same time Typically interacts directly with end-users using a
Graphical User Interface (GUI) Server
Waits for requests from clients Upon receipt of requests, processes them and then serves
replies Usually accepts connections from a large number of
clients Typically does not interact directly with end-users
Transaction Processing Example
Transaction –Get Balance in a Bank Account Steps
User initiates request giving bank account number (Client program )
Main Server at Bank (Server program) services the request by contacting the Database server
o Sends a request (Client Program) to the Database Server along with the bank account number
o Database Server (Server Program) retrieves the bank balance using the bank account number and returns the value
Main server at Bank (Server Program) returns the balance amount to the user (Client Program)
AU Distance Education – DMC1754 - Middleware Technologies - Unit I
CLIENT / SERVER Transaction Processing
CLIENT
MAIN SERVER
DATABASE SERVER
1
2
3
4
CLIENT/SERVERARCHITECTURE IN THE WEB
World Wide Web (WWW) or Web revolves around the client/server architecture
Client computer system uses Browsers ( like Internet Explorer, Netscape Navigator, Mozilla etc. ) to interact with Internet servers using Protocols
Protocols help in the accurate transfer of data - requests from browser & responses from server
Commonly used protocols : HTTP (Hyper Text Transfer Protocol) FTP (File Transfer Protocol) SMTP (Simple Mail Transfer Protocol)
Client / Server Model Static HTML Pages
Client / Server Model Dynamic HTML Pages
Client / Server Model Server – side Scripting
Types of Servers
File ServerDatabase ServerApplication ServerWeb ServerObject ServerOthers – Chat Server, Fax Server, Mail
server, News Server …
FILE SERVER
FILE SERVER
Objectives of File Server To promote sharing of files (computer
programs and/or data) To encourage indirect or implicit (via
programs) use of remote computers To shield a user from variations in file storage
systems among hosts To transfer data reliably and efficiently
Database Server
A computer in a LAN dedicated to database storage and retrieval
The database server holds the Database Management System (DBMS) and the databases
Upon requests from the client machines, it searches the database for selected records and passes them back over the network
Database Server - Example
Software Project Team – sharing a database
APPLICATION SERVER
Application server runs the programs and processes the data
Application servers are typically used for complex transaction-based applications
Application server performs the business logic functions and some data access
An application server provides middle tier processing between the user's machine and the database management system (DBMS)
Web Server
Web Server delivers web pages to browsers
Client/Server Application
Has three functional units: Presentation logic or user interface (for example,
ATM machines) Business logic (for example software that enables
a customer to request an account balance) Data (for example, records of customer accounts)
Functional units can reside on the client or on multiple servers
Middleware is the software that connects / communicates between client and server
Two-Tier Architecture
Two-Tier Architecture - Internet
Three -Tier Architecture
Three -Tier Architecture
The Middle Tier can be A Transaction Processing Monitor A Message Server An Application Server An Object Server
Three -Tier Architecture - Internet
Multi -Tier Architecture
Multi -Tier Architecture
Multi -Tier Architecture
Advantages of Client/Server
Distribution or sharing of processing load among several independent computers
Centralized data storage on server, hence easy to implement security of data access
Clients with the appropriate permissions may be permitted to access and change data
Centralized data. Hence easy to administer Is capable of functioning with multiple
different clients each with different capabilities
Disadvantages of Client/Server
Traffic congestion on the network (number of simultaneous client requests to a server) can cause a server to become overloaded and unable to service client’s requests
Under client-server, should a critical server fail, clients’ requests cannot be fulfilled. Hence, lack of robustness is a cause for concern
Summary
The following concepts have been covered Evolution of client / server architecture Client / Server architecture Characteristics of client / server model Different types of servers Client / server on the Internet Different types of client/server models Advantages and Disadvantages of Client/Server
Architecture
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