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Unit – I CLIENT / SERVER ARCHITECTURE
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Unit Structure Evolution of Client/Server Architecture Client/Server Model Characteristics of Client/Server Model Client/Server Architecture in the Web Types of Servers Types of Client/Server Models Advantages & Disadvantages of Client/Server Model
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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
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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
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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
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CLIENT / SERVER MODEL Servers typically contain data files & applications accessed by multiple clients Client & Server share the processing load Client / Server can be on same computer system or on different computer systems Client/Server model - a convenient way to interconnect programs distributed across different locations
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CLIENT / SERVER MODEL Client initiates request Server services request SERVER CLIENT
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CLIENT / SERVER MODEL Server can range from PCs to mainframes Standard Server hardware Support for large amount of RAM Fast input and output Fast network cards Ability to support multiple processors Support for fault tolerance
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Characteristics of Client/Server Model Asymmetrical protocols Encapsulation of services Location transparency Message-based exchanges Modular, Extensible design Platform Independence Scalability Separation of Client/Server Functionality Shared resources
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Characteristics of Client/Server Model Benefits Provided by Server Optimization Centralization Data Integity Security Back-up
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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
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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 oSends a request (Client Program) to the Database Server along with the bank account number oDatabase 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)
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AU Distance Education – DMC1754 - Middleware Technologies - Unit I CLIENT / SERVER Transaction Processing CLIENT MAIN SERVER DATABASE SERVER 1 2 3 4
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CLIENT/SERVER ARCHITECTURE 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)
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Client / Server Model Static HTML Pages
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Client / Server Model Dynamic HTML Pages
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Client / Server Model Server – side Scripting
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Types of Servers File Server Database Server Application Server Web Server Object Server Others – Chat Server, Fax Server, Mail server, News Server …
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FILE SERVER
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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
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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
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Database Server - Example Software Project Team – sharing a database
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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)
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Web Server Web Server delivers web pages to browsers
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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
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Two-Tier Architecture
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Two-Tier Architecture - Internet
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Three -Tier Architecture
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The Middle Tier can be A Transaction Processing Monitor A Message Server An Application Server An Object Server
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Three -Tier Architecture - Internet
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Multi -Tier Architecture
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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
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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
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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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