Unit 1
- 1. Distributed Systems BY K.KARTHICK, AP/CSE KONGUNADU COLLEGE OF ENGINEERING AND TECHNOLOGY, TRICHY
- 3. Outline • Definition of a Distributed System • Needs of a Distributed System • Examples of distributed system • Trends in distributed system • Focus on resource sharing • Challenges • Case study: WWW
- 4. What Is A Distributed System? • A collection of independent computers that appears to its users as a single coherent system. • A distributed system is a set of networked computers communicate and coordinate their actions by passing messages. • Features: – No shared memory – message-based communication – Each runs its own local OS – Heterogeneity
- 5. Distributed System A distributed system organized as middleware. Note that the middleware layer extends over multiple machines. 1.1
- 6. Need of distributed systems • Resource sharing • fault tolerance • security • Reliability • Concurrent transactions
- 7. 1.2 Distributed System Characteristics • Multiple autonomous components • Components are not shared by all users • Resources may not be accessible • Software runs in concurrent processes on different processors • Multiple Points of control • Multiple Points of failure
- 8. Advantages • Economics- which increases computational speed • Speed- more number of system can be added to increase computational speed. • Reliability - works even in failure mode. • Extensibility- computers and software can be added incrementally.
- 9. Centralized system Distributed system CS have non –autonomous components DS have autonomous system Multiple users share the resources centralized at all times DS have components in concurrent process CS have a Single point of failure DS have multiple point of failure.
- 10. Advantages of Distributed vs Standalone systems • Data sharing- multiple users can access common database, data files • Extensibility- add resources and software's as Needed. Resource sharing- resources can be shared across all the devices in the network
- 11. Examples of distributed systems • Web search • Massively multiplayer online games • Financial trading
- 12. Web search • searching is the most important activity in web. • Web search stores all formats of web pages. • search engine is a computer program that searches for particular keywords and returns a list of documents. – search by keywords – Search by categories – Specialize in language searching
- 13. Massively multiplayer online games • A massively multi player online games which is capable of supporting large number of players simultaneously. • These games can be able to co-operate and compete each other in a large scale. • Challenges: – Fast response needed
- 14. Financial trading • Finance industry used the wide application of distributed system for real time access and automation process. • Share market which includes economic and political development. Where in communication and data process is a distributed approach.
- 15. • Local Area Network and Intranet • Database Management System • Automatic Teller Machine Network • Internet/World-Wide Web • Mobile and ubiquitous computing • Air traffic control
- 16. 2.1 Local Area Network Name Server: Machine -> IP address User name -> user id Group name -> group id the rest of email server Web server Desktop computers File serv er router/firewall print and other serv ers other servers print Local area network email server the Internet
- 17. 2.2 Database Management System
- 18. 2.3 Automatic Teller Machine Network
- 19. 2.4 Internet intranet ISP desktop computer: backbone satellite link server: % network link: % % %
- 21. 2.4.2 Web Servers and Web Browsers Internet Browsers Web servers www.google.com www.cse.cuhk.edu.hk www.w3c.org Protocols Activity.html http://www.w3c.org/Protocols/Activity.html http://www.google.comlsearch?q=lyu http://www.cse.cuhk.edu.hk/ File system of www.w3c.org
- 22. Disadvantages • Implementing Distributed systems is much difficult • security issues • saturation
- 23. Trends in distributed system • Stand-alone workstations delivering several tens of millions of operations per second are commonplace, and continuing increases in power are predicted. • When these computer systems are interconnected by an appropriate high-speed network, their combined computational power can be applied to solve a variety of computationally intensive applications
- 24. • pervasive networking and modern internet • Mobile and ubiquitous computing • distributed multimedia systems • Distributed computing as a utility
- 25. pervasive networking and modern internet • Internet – The modern Internet is a vast interconnected collection of computer networks of many different types, with the range of types increasing all the time and now including – for example, a wide range of wireless communication technologies such as WiFi, WiMAX, Bluetooth and third-generation mobile phone networks.
- 27. Intranet
- 28. Mobile and ubiquitous computing • Technological advances in device miniaturization and wireless networking have led increasingly to the integration of small and portable computing devices into distributed systems.
- 29. • Laptop computers. • Handheld devices, including mobile phones, smart phones, GPS-enabled devices, pagers, personal digital assistants (PDAs), video cameras and digital cameras. • Wearable devices, such as smart watches with functionality similar to a PDA. • Devices embedded in appliances such as washing machines, hi-fi systems, cars and refrigerators.
- 30. 2.5 Mobile and Ubiquitous Computing Laptop Mobile Printer Camera Internet Host intranet Home intranet GSM/GPRS Wireless LAN phone gateway Host site
- 31. Distributed multimedia system • Computer controlled integration of text, graphics, still images, moving pictures, animation, sound. • it able to store and locate audio or video files to transmit across the network to support the presentation of the media types to the user and optionally also to share media. Across a group of users.
- 32. RESOURCE SHARING • Is the primary motivation of distributed computing. • Resource sharing in a distributed system are encapsulated within one computer and can only be accessed from other computers by communication.
- 33. • Ability to use any hardware, software or data anywhere in the system. • Resource manager controls access, provides naming scheme and controls concurrency. • Resource sharing model (e.g. client/server or object-based) describing how – resources are provided they are used – provider and user interact with each other
- 34. • Resources types • Hardware, e.g. printer, scanner, camera • Data, e.g. file, database, web page • More specific functionality, e.g. search engine, file • Service • manage a collection of related resources and present their functionalities to users and applications
- 35. • Server – process on networked computer that accepts requests from processes on other computers to perform a service and responds appropriately. – Able to split the resources based on request.
- 36. • Hardware resources – CPU – Memory unit – Disk – Screen – printer • Software resources. – Web pages – Files – Database – Video/audio streams
- 37. THE CHALLENGES IN DISTRIBUTED SYSTEM • Heterogeneity • Openness • Security • Scalability • Failure handling • Concurrency • Transparency • Quality of service
- 38. Heterogeneity • The Internet enables users to access services and run applications over a heterogeneous • collection of computers and networks. Heterogeneity (that is, variety and difference) applies to all of the following: • networks; • computer hardware; • operating systems; • programming languages; • implementations by different developers
- 39. • Middleware services: – COBRA(Common Object request Broker Architecture) – DCOM(Distributed Component Object Model)
- 40. Openness • The openness of a computer system is the characteristic that determines whether the system can be extended and reimplemented in various ways. • The openness of distributed systems is determined primarily by the degree to which new resource-sharing services can be added and be made available for use by a variety of client programs.
- 41. Security • Many of the information resources that are made available and maintained in distributed systems have a high intrinsic value to their users. Their security is therefore of considerable importance. • Security for information resources has three components: confidentiality (protection against disclosure to unauthorized individuals), • integrity (protection against alteration or corruption) • availability (protection against interference with the means to access the resources).
- 42. Scalability • A system is said to be scalable of it handle the addition of users and resources without suffering loss of performance or increase in complexity. – In size – In location – In administration (regions and ownership)
- 43. File Handling • Computer systems sometimes fail. When faults occur in hardware or software, programs may produce incorrect results or may stop before they have completed the intended computation. – Denial of service
- 44. Concurrency • Components executed in distributed system in concurrent process. • It should be able to handle several clients will attempt to access a shared resources at same time. • Multiple resources make request to read, write, and update operation.
- 45. Transparency • Transparency is defined as the concealment from the user and the application programmer of the separation of components in a distributed system, so that the system is perceived as a whole rather than as a collection of independent components. • The implications of transparency are a major influence on the design of the system software.
- 46. • Access transparency – enables local and remote resources to be accessed using identical operations. • Location transparency – enables resources to be accessed without knowledge of their physical or network location
- 47. CASE STUDY:WWW • www is an largest application of distributed systems for publishing and accessing resources and services across the internet • www is a collection of millions of file stored on thousands of servers over the world. These files contain documents, files, pictures, video and audio files.
- 48. • A web server is a computer connected to internet that runs a program takes the responsibility for storing, retrieving and distributing contents on the web. • HTML is the universal language used in web. • Javascripts, VB script are some of the language used in web
- 49. • A web page is an HTML document that stored on web server, a web site is a collection of web pages that ate interlinked to each other. • A web browser is a program which is used to communicate with the web servers on internet. • Web crawlers (Spider)is program used by Google. • Internet explorer, Netscape navigator, Mozilla Firefox, are some of the example of web browser.