1. Unit – I CLIENT / SERVER ARCHITECTURE

2. 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

3. 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

4. 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

5. 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

6. 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

7. CLIENT / SERVER MODEL Client initiates request Server services request SERVER CLIENT

8. 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

9. 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

10. Characteristics of Client/Server Model  Benefits Provided by Server  Optimization  Centralization  Data Integity  Security  Back-up

11. 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

12. 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)

13. AU Distance Education – DMC1754 - Middleware Technologies - Unit I CLIENT / SERVER Transaction Processing CLIENT MAIN SERVER DATABASE SERVER 1 2 3 4

14. 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)

15. Client / Server Model Static HTML Pages

16. Client / Server Model Dynamic HTML Pages

17. Client / Server Model Server – side Scripting

18. Types of Servers  File Server  Database Server  Application Server  Web Server  Object Server  Others – Chat Server, Fax Server, Mail server, News Server …

19. FILE SERVER

20.  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

21. 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

22. Database Server - Example Software Project Team – sharing a database

23. 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)

24. Web Server Web Server delivers web pages to browsers

25. 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

26. Two-Tier Architecture

27. Two-Tier Architecture - Internet

28. Three -Tier Architecture

29.  The Middle Tier can be  A Transaction Processing Monitor  A Message Server  An Application Server  An Object Server

30. Three -Tier Architecture - Internet

31. Multi -Tier Architecture

34. 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

35. 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

36. 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