1. Characterization of Distributed Systems From Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edition 4, © Pearson Education 2005

2. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Networking and Parallel Computing zComputer networking yHardware that connects computers ySoftware that sends/receives messages from one computer to another, which might be on different networks (end to end delivery) yGoal is to transmit messages reliably and efficiently zParallel Computing yMultiple homogeneous processors in “one” computer yShared or distributed memory yGoal is to execute a program faster by division of labor

3. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Distributed Computing zNetworked computers that could be far apart yrely on computer networking zCommunicate and coordinate by sending messages zGoal is to share (access/provide) distributed resources zIssues: yConcurrent execution of processes yNo global clock for coordination yMore components, more independent failures

4. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Examples of Distributed Systems zGlobal Internet zOrganizational Intranets--behind router/firewall zMobile Computing -- computers move zUbiquitous Computing -- computers embedded everywhere zIssues: ydiscovery of resources in different host environments ydynamic reconfiguration ylimited connectivity yprivacy and security guarantees to the user and the host environment

5. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 A Typical Portion of the Internet

6. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 A Typical Intranet

7. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Portable and handheld devices

8. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Resource Sharing and the Web zHTML, Hyper Text Markup Language zURL, Uniform Resource Locator y http://servername[:port] [/pathname] [?arguments] zHTTP, HyperText Transfer Protocol yrequest-reply protocol (client-server) ycontent types--MIME types, multipurpose internet mail extensions yone resource per request ysimple access control (mostly public)

9. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Web Servers and Web Browsers Internet Browsers Web servers www.google.com www.cdk3.net www.w3c.org Protocols Activity.html http://www.w3c.org/Protocols/Activity.html http://www.google.comlsearch?q=kindberg http://www.cdk3.net/ File system of www.w3c.org

10. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Other Web Technologies zweb forms zCGI programs, common gateway interface, run on the server zapplets, run on the client zRDF, resource description framework, vocabulary for meta-data zXML, extensible markup language, allow meta-data information to be included

11. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Computers in the Internet Date Computers Web servers 1979, Dec. 1880 1989, July130,0000 1999, July56,218,0005,560,866 2003, Jan.171,638,29735,424,956

12. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Computers vs. Web servers in the Internet 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

13. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Challenges and Issues (1) zHeterogeneity ynetworks, hardware, os, languages... ymiddleware—corba y mobile code, virtual machines zOpenness yextended and re-implemented in various ways ystandard published interfaces yRFC, request for comments zSecurity yconfidentiality yintegrity yavailability

14. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Challenges and Issues (2) zScalability yeffective with significant increase in resources ycost yperformance zFailure handling ydetecting ymasking—hide, less severe (retransmit) ytolerating--ignore, timeout yrecovery--logs, rollback yRedundancy zConcurrency

15. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Challenges and Issues (3) zTransparency yAccess transparency: enables local and remote resources to be accessed using identical operations. yLocation transparency: enables resources to be accessed without knowledge of their physical or network location (for example, which building or IP address). yConcurrency transparency: enables several processes to operate concurrently using shared resources without interference between them. yReplication transparency: enables multiple instances of resources to be used to increase reliability and performance without knowledge of the replicas by users or application programmers.

16. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Challenges and Issues (4) zTransparency yFailure transparency: enables the concealment of faults, allowing users and application programs to complete their tasks despite the failure of hardware or software components. yMobility transparency: allows the movement of resources and clients within a system without affecting the operation of users or programs. yPerformance transparency: allows the system to be reconfigured to improve performance as loads vary. yScaling transparency: allows the system and applications to expand in scale without change to the system structure or the application algorithms.