Characterization of Distributed Systems From Coulouris Dollimore and

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

Networking and Parallel Computing z Computer networking y. Hardware that connects computers y. Software that sends/receives messages from one computer to another, which might be on different networks (end to end delivery) y. Goal is to transmit messages reliably and efficiently z Parallel Computing y. Multiple homogeneous processors in “one” computer y. Shared or distributed memory y. Goal is to execute a program faster by division of labor Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

Distributed Computing z Networked computers that could be far apart yrely on computer networking z Communicate and coordinate by sending messages z Goal is to share (access/provide) distributed resources z Issues: y. Concurrent execution of processes y. No global clock for coordination y. More components, more independent failures Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

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

A Typical Portion of the Internet intranet ISP % % backbone satellite link desktop computer: server: network link: Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

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

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

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

Web Servers and Web Browsers http: //www. google. comlsearch? q=kindberg www. google. com Browsers Web servers Internet www. cdk 3. net http: //www. cdk 3. net/ www. w 3 c. org File system of www. w 3 c. org Protocols http: //www. w 3 c. org/Protocols/Activity. html Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

Other Web Technologies z web forms z CGI programs, common gateway interface, run on the server z applets, run on the client z RDF, resource description framework, vocabulary for meta-data z XML, extensible markup language, allow meta-data information to be included Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

Computers in the Internet Date 1979, Dec. 1989, July 1999, July 2003, Jan. Computers Web servers 188 0 130, 000 56, 218, 000 171, 638, 297 0 5, 560, 866 35, 424, 956 Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

Computers vs. Web servers in the Internet Date 1993, July 1995, July 1997, July 1999, July 2001, July Computers Web servers Percentage 1, 776, 000 130 0. 008 6, 642, 000 19, 540, 000 56, 218, 000 125, 888, 197 23, 500 1, 203, 096 6, 598, 697 31, 299, 592 42, 298, 371 0. 4 6 12 25 Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

Challenges and Issues (1) z Heterogeneity y networks, hardware, os, languages. . . y middleware—corba y mobile code, virtual machines z Openness y extended and re-implemented in various ways y standard published interfaces y RFC, request for comments z Security y confidentiality y integrity y availability Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

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

Challenges and Issues (3) z Transparency y. Access transparency: enables local and remote resources to be accessed using identical operations. y. Location transparency: enables resources to be accessed without knowledge of their physical or network location (for example, which building or IP address). y. Concurrency transparency: enables several processes to operate concurrently using shared resources without interference between them. y. 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. Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

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