1. Distributed Systems: Concepts and Design Edition 5, © Addison-Wesley 2012 Chapter 1 Characterization of Distributed Systems

2. Distributed System  System in which hardware or software components located at networked computers communicate and coordinate their actions by passing messages.  Consequences of Distributed Systems: Concurrency: All users can work in the same time, sharing resources No global clock: there is no global time for exchanging messages Independent failures: Failure in the network results in the isolation of the computers that are connected to it, The failure of a computer will not affect other computers. 2

3. Examples of Distributed Systems 1.Web 3

4. 4 Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012 Figure 1.1 Selected application domains and associated networked applications Finance and commerceeCommerce e.g. Amazon and eBay, PayPal, online banking and trading The information society Web information and search engines, ebooks, Wikipedia; social networking: Facebook. Entertainmentonline gaming, music and film in the home, user- generated content, e.g. YouTube, Flickr Healthcarehealth informatics, on online patient records, monitoring patients Educatione-learning, virtual learning environments; distance learning Transport and logisticsGPS in route finding systems, map services: Google Maps, Google Earth ScienceEnabling technology for collaboration between scientists Environmental managementsensor technology to monitor earthquakes, floods or tsunamis

5. 5 Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012 2. Financial trading system

6. Examples : share prices and trends, economic developments. Automated monitoring and trading applications Examples of events include a drop in a share price CEP: compose event occurrences together into logical, temporal or spatial patterns Event sources are of different formats, such as: Reuters events and FIX events FIX events: following format of Financial Information eXchange protocol 6

7. Trends in Distributed Systems 7

8. Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012 Figure 1.1 A typical portion of the Internet

9. Intranet: sub-networks operated by companies and other organizations and protected by firewalls. Firewall: Protect an intranet by preventing unauthorized messages from leaving or entering, by filtering in and out messages ISP: Companies that provide connections to users and organizations enabling them to access services in the Internet. Backbone: network link with a high transmission capacity, it uses satellite connections, fiber optic cables,… 9

10. Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012 Figure 1.2 Portable and handheld devices in a distributed system

11. 11 Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012 Figure 1.3 Cloud computing

12. A cloud is defined as a set of Internet-based application, storage and computing services to support users’ needs Everything as a service, often paid for on a per-usage basis rather than purchased Clouds are generally implemented on cluster computers A cluster computer is a set of interconnected computers that cooperate closely to provide a single, integrated high performance computing capability 12

13. Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012 Growth of the Internet (computers and web servers) DateComputersWeb serversPercentage 1993, July 1,776,0001300.008 1995, July6,642,00023,5000.4 1997, July19,540,0001,203,0966 1999, July56,218,0006,598,69712 2001, July125,888,19731,299,59225 42,298,371 2003, July 2005, July ~200,000,000 353,284,18767,571,581 21 19

14. Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012 Transparencies 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 (for example, which building or IP address). Concurrency transparency: enables several processes to operate concurrently using shared resources without interference between them. Replication transparency: enables multiple instances of resources to be used to increase reliability and performance without knowledge of the replicas by users or application programmers. Failure transparency: enables the concealment of faults, allowing users and application programs to complete their tasks despite the failure of hardware or software components. Mobility transparency: allows the movement of resources and clients within a system without affecting the operation of users or programs. Performance transparency: allows the system to be reconfigured to improve performance as loads vary. Scaling transparency: allows the system and applications to expand in scale without change to the system structure or the application algorithms.

15. Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012 Case Study Web servers and web browsers Internet Browsers Web servers www.google.com www.cdk5.net www.w3c.org standards faq.html http://www.w3.org/standards/faq.html#conformance http://www.google.comlsearch?q=obama http://www.cdk5.nethttp://www.cdk5.net/ File system of www.w3c.org