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Distributed System ppt
- 1. www.oeclib.in Submitted By: Odisha ElectronicsControl Library Seminar On Distributed Systems
- 2. CONTENT What isa Distributed System Types of Distributed Systems Examples of Distributed Systems Common Characteristics Basic Design Issues Advantages Disadvantages Conclusion 2
- 3. 1. WHAT ISA DISTRIBUTED SYSTEM? Definition: A distributed system is one in which components located at networked computers communicate and coordinate their actions only by passing messages. This definition leads to the following characteristics of distributed systems: Concurrency of components Lack of a global ‘clock’ Independent failures of components 3
- 4. 2. TYPES OFDISTRIBUTED SYSTEMS Distributed Computing Systems. Distributed Information Systems. Distributed Pervasive Systems. Distributed Computing Systems: The distributed computing systems include the following: Cluster computing systems Grid computing systems 4
- 5. Distributed Informative Systems:In the distributed systems, the following forms are concentrated: Transaction processing systems Enterprise application integration Distributed Pervasive Systems: Few examples of distributed pervasive systems are as below: Home systems Electronic health care systems Sensor networks 5
- 6. 3. EXAMPLES OFDISTRIBUTED SYSTEMS Local Area Network and Intranet Database Management System Automatic Teller Machine Network Internet/World-Wide Web Mobile and Ubiquitous Computing 6
- 7. 3.1 LOCAL AREANETWORK the rest of em ail server Web server Desktop computers File serv er router/firewall print and other serv ers other servers print Local area network em ail server the Internet 7
- 8. 3.2 DATABASE MANAGEMENTSYSTEM 8
- 9. 3.3 AUTOMATIC TELLERMACHINE NETWORK 9
- 10. 3.4 INTERNET intranet ISP desktop computer: backbone satellitelink server: % network link: % % % 10
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- 12. 3.4.2 WEB SERVERSAND WEB BROWSERS Internet Browsers Web servers www.google.com www.uu.se www.w3c.org Protocols Activity.html http://www.w3c.org/Protocols/Activity.html http://www.google.comlsearch?q=lyu http://www.uu.se/ File system of www.w3c.org 12
- 13. 3.5 MOBILE ANDUBIQUITOUS COMPUTING Laptop Mobile Printer Camera Internet Host intranet Home intranet GSM/GPRS Wireless LAN phone gateway Host site 13
- 14. 4. COMMON CHARACTERISTICS What are we trying to achieve when we construct a distributed system? Certain common characteristics can be used to assess distributed systems Heterogeneity Openness Security Scalability Failure Handling Concurrency Transparency 14
- 15. 4.1 HETEROGENEITY Varietyand differences in Networks Computer hardware Operating systems Programming languages Implementations by different developers Middleware as software layers to provide a programming abstraction as well as masking the heterogeneity of the underlying networks, hardware, OS, and programming languages (e.g., CORBA). Mobile Code to refer to code that can be sent from one computer to another and run at the destination (e.g., Java applets and Java virtual machine). 15
- 16. 4.2 OPENNESS Opennessis concerned with extensions and improvements of distributed systems. Detailed interfaces of components need to be published. New components have to be integrated with existing components. Differences in data representation of interface types on different processors (of different vendors) have to be resolved. 16
- 17. 4.3 SECURITY Ina distributed system, clients send requests to access data managed by servers, resources in the networks: Doctors requesting records from hospitals Users purchase products through electronic commerce Security is required for: Concealing the contents of messages: security and privacy Identifying a remote user or other agent correctly (authentication) New challenges: Denial of service attack Security of mobile code 17
- 18. 4.4 SCALABILITY Adaptationof distributed systems to accommodate more users respond faster (this is the hard one) Usually done by adding more and/or faster processors. Components should not need to be changed when scale of a system increases. Design components to be scalable! 18
- 19. 4.5 FAILURE HANDLING(FAULT TOLERANCE) Hardware, software and networks fail! Distributed systems must maintain availability even at low levels of hardware/software/network reliability. Fault tolerance is achieved by recovery redundancy 19
- 20. 4.6 CONCURRENCY Componentsin distributed systems are executed in concurrent processes. Components access and update shared resources (e.g. variables, databases, device drivers). Integrity of the system may be violated if concurrent updates are not coordinated. Lost updates Inconsistent analysis 20
- 21. 4.7 TRANSPARENCY Distributedsystems should be perceived by users and application programmers as a whole rather than as a collection of cooperating components. Transparency has different aspects. These represent various properties that distributed systems should have. 21
- 22. 5. BASIC DESIGNISSUES General software engineering principles include rigor and formality, separation of concerns, modularity, abstraction, anticipation of change, … Specific issues for distributed systems: Naming Communication Software structure System architecture Workload allocation Consistency maintenance 30
- 23. 5.1 NAMING Aname is resolved when translated into an interpretable form for resource/object reference. Communication identifier (IP address + port number) Name resolution involves several translation steps Design considerations Choice of name space for each resource type Name service to resolve resource names to comm. id. Name services include naming context resolution, hierarchical structure, resource protection 31
- 24. 5.2 COMMUNICATION Separatedcomponents communicate with sending processes and receiving processes for data transfer and synchronization. Message passing: send and receive primitives synchronous or blocking asynchronous or non-blocking Abstractions defined: channels, sockets, ports. Communication patterns: client-server communication (e.g., RPC, function shipping) and group multicast 32
- 25. 5.3 SOFTWARE STRUCTURE Layers in centralized computer systems: Applications Middleware Operating system Computer and Network Hardware 33
- 26. 5.3 SOFTWARE STRUCTURE Layers and dependencies in distributed systems: Applications Distributed programming support Open services Open system kernel services Computer and network hardware 34
- 27. 5.4 SYSTEM ARCHITECTURES Client-Server Peer-to-Peer Services provided by multiple servers Proxy servers and caches Mobile code and mobile agents Network computers Thin clients and mobile devices 35
- 28. 5.4.1 CLIENTS INVOKEINDIVIDUAL SERVERS Serv er Client Client inv ocation result Serv erinv ocation result Process: Key: Computer: 36
- 29. 5.4.2 PEER-TO-PEER SYSTEMS Application Application Application Peer1 Peer 2 Peer 3 Peers 5 .... N Sharable objects Application Peer 4 37
- 30. 5.4.3 A SERVICEBY MULTIPLE SERVERS Serv er Serv er Serv er Serv ice Client Client 38
- 31. 5.4.4 WEB PROXYSERVER Client Proxy Web server Web server server Client 39
- 32. 5.4.5 WEB APPLETS a)client request results in the downloading of applet code Web server Client Web serverApplet Applet code Client b) client interacts with the applet 40
- 33. 5.4.6 THIN CLIENTSAND COMPUTE SERVERS Thin Client Application Process Network computer or PC Compute server network 41
- 34. 6.ADVANTAGES Sharing Data: There is a provision in the environment where user at one site may be able to access the data residing at other sites. Autonomy : Because of sharing data by means of data distribution each site is able to retain a degree of control over data that are stored locally. Availability : If one site fails in a distributed system, the remaining sites may be able to continue operating. Thus a failure of a site doesn't necessarily imply the shutdown of the System. 42
- 35. 7. DISADVANTAGES SoftwareDevelopment Cost Greater Potential for Bugs increased Processing Overhead 43
- 36. REFERENCES www.google.com www.wikipedia.com www.oeclib.in
- 37.