1. 1 Distributed Computing Class: BIT 5 & 6 Instructor: Aatif Kamal Chapter 01: Character of Distributed Systems Dated: 06 th Sept 2006

2. Copyrights @ 2006-7, Aatif Kamal2 Objectives: course The aims of this course is to study the fundamental characteristics of distributed systems; their models and architectures; the design of distributed algorithms and applications that exploit rapidly evolving technology Theory: To study the principles of distributed systems To grasp the basic issues of the distributed systems Practice: To design and implement basic distributed system as a client/server and a number of other ways

3. Copyrights @ 2006-7, Aatif Kamal3 Course Structure Characteristics of Distributed Systems (1.5 Wks) Introduction to Distributed systems and Examples, Resource sharing and Challenges. Distributed System Models. (2 Wks) Architectural models and Fundamental models Networking and Internetworking (Special Classes/Self Study) Types of network, Network principles, Internet protocols, Network case studies: ATM Interprocess Communication (2 Wks) APIs for the Internet protocols, External data representation and marshalling, Client-server communication, Group communication

4. Copyrights @ 2006-7, Aatif Kamal4 Course Structure Distributed Objects and Remote Invocation (2 Wks) Communication between distributed objects, Remote procedure call, Events and notifications, Java RMI case study. Security (Special Classes/Self Study) Overview of security techniques, Cryptographic algorithms, Digital signatures, Cryptography pragmatics, Case studies: Needham-Schroeder, Kerberos, SSL & Millicent Peer to Peer Computing (2 Wks) P2P Introduction, Napster & its lageacy, P2P middleware, Routing Overlays, Overlay case studies: Pastry, Tpastery, Squirrel, Oceanstore, Ivy and JAXTA Time and Global States (2 Wks) Clocks, events and process states, Synchronizing physical clocks, Logical time and logical clocks, Global states, Distributed debugging.

5. Copyrights @ 2006-7, Aatif Kamal5 BOOKS TEXT BOOK Distributed Systems: Concepts and Design (Fourth/Third Edition) By George Coulouris, Jean Dollimore and Tim Kindberg Addison-Wesley, ©Pearson Education 2001 REFERENCE BOOKS Distributed Systems: Principles and Paradigms, By Andrew S. Tanenbaum and van Steen Distributed Operating System and Algorithms, By Randy Chow & Theodore Johnson.

6. Copyrights @ 2006-7, Aatif Kamal6 Course Grading Quizzes/Assignment:15 % Course Project:10 % OHTs :30 % Final Test:45 % Open :05 %

7. Copyrights @ 2006-7, Aatif Kamal7 Definition of Distributed System A distributed system is: Components located at networked computers communicate and coordinate their actions by passing messages A distributed system is: Collection of independent computers that appear to the users of the system as a single computer [Tanenbaum]

8. Copyrights @ 2006-7, Aatif Kamal8 Definition of Distributed System Machine B Local OS Machine A Local OS Machine C Local OS Network Distributed applications Middleware service

9. Copyrights @ 2006-7, Aatif Kamal9 Definition of Distributed System "a collection of autonomous computers linked by a computer network with distributed system software" "a collection of processors interconnected by a communication network in which each processor has its own local memory and other peripherals and the communication between any two processors of the system takes place by message passing over the communication network" "one in which hardware or software components located at networked computers communicate and coordinate their actions only by passing messages"

10. Copyrights @ 2006-7, Aatif Kamal10 Definition of Distributed System In other words, to the user, a DS looks like a single system a virtual uniprocessor The user doesn't know (or care) - where (on what machine) files are located - where a job is executed A Distributed System is made of several computers which have no shared memory have no shared clock communicate with each other via messages have their own operating systems

11. Copyrights @ 2006-7, Aatif Kamal11 Advantages Why distributed systems Resource sharing Communication Inherent distribution Speed 10000 CPU running at speed of 50 MIPS 500000 MIPS Economy Incremental growth Reliability

12. Copyrights @ 2006-7, Aatif Kamal12 Characteristics of DS Concurrency Distributed systems are concurrent systems Every software or hardware components is autonomous  Process Concurrent tasks  A and B are concurrent if either A can happen before B or B can happen before A Synchronization and coordination by message passing Lack of global clock Coordination and time Independent failure Failures of individual processes may remain undetected

13. Copyrights @ 2006-7, Aatif Kamal13 Examples of Distributed Systems 1. The internet Heterogeneous network of computers and applications Implemented through Internet protocol

14. Copyrights @ 2006-7, Aatif Kamal14 Examples of Distributed Systems 2. Distributed multimedia Often use the Internet infrastructure Characteristics Heterogeneous data sources that need to be synchronized in real time Video, Audio, Text Often: distribution services multicast Examples Tele teaching, Video conferencing

15. Copyrights @ 2006-7, Aatif Kamal15 Examples of Distributed Systems 3. Intranet Locally administered network Usually proprietary Interfaces with the Internet via router Firewall the rest of email server Web server Desktop computers File server router/firewall print and other servers other servers print Local area network email server the Internet Issues File services need to share data Firewall impede Legitimate access

16. Copyrights @ 2006-7, Aatif Kamal16 Examples of Distributed Systems (1) 4. Mobile and Ubiquitous computing Resource Sharing while on the move Primary concerns: resource discovery efficient use of limited bandwidth security (privacy)

17. Copyrights @ 2006-7, Aatif Kamal17 Resource sharing and the Web Resource sharing pattern Search engine CSCW Computer-supported cooperative work Service Software that manages a collection of resources and presents them to users and applications via a well-defined interface Server Running program (a process that provide one or more services) Remote invocation Client’s request to server.

18. Copyrights @ 2006-7, Aatif Kamal18 Challenges A number of challenges arises: Heterogeneity Openness Security Scalability Failure handling Concurrency of components Transparency

19. Copyrights @ 2006-7, Aatif Kamal19 Challenges Heterogeneity networks computer hardware Operating systems Programming languages Middleware To over come differences in network, OS and languages CORBA

20. Copyrights @ 2006-7, Aatif Kamal20 Challenges Openness Ensures extensibility and maintainability of the system Standard interfaces & their publication Addition of new resources RFC (Request for comments) specification for internet protocols. www. ietf.org Benefits of ODS key interfaces are published uniform communication mechanisms and access to shared resources Construction Heterogeneous components

21. Copyrights @ 2006-7, Aatif Kamal21 Challenges Security confidentiality integrity availability Example A doctor might request access to hospital patient data In electronic commerce and banking, users send their credit card numbers across the internet Current security challenges Denial of service attack Security of mobile code

22. Copyrights @ 2006-7, Aatif Kamal22 Challenges Scalability Controlling the cost of the physical resources Does the system remain effective given the expected growth Controlling the performance loss www.amzon.com is more than one computer www.amzon.com Preventing the software resources running out IP addressees :32 bits to 128 Avoiding performance bottleneck  Decentralization of data/information

23. Copyrights @ 2006-7, Aatif Kamal23 Challenges Computers vs. Web servers in the Internet DateComputersWeb serversPercentage 1993, July 1,776,000 130 0.008 1995, July6,642,000 23,500 0.4 1997, July19,540,0001,203,0966 1999, July56,218,0006,598,697 12 Mid. 2002 Internet : 150 million+ computers 667 million people 2.5 billion+ web pages

24. Copyrights @ 2006-7, Aatif Kamal24 Challenges Failure handling Detecting failure Checksum can be used to detect corrupted data System crash (impossible) Masking Retransmission Redundant storage Tolerating failure Exception handling (timeout when waiting for web source)

25. Copyrights @ 2006-7, Aatif Kamal25 Challenges Failure handling Recovery from failure Roll back Redundancy Redundant routes in network Replication of name tables in multiple domain name servers Database replication Availability Measure of the proportion of the time a server is available

26. Copyrights @ 2006-7, Aatif Kamal26 Challenges Concurrency Consistent scheduling of threads (so that dependencies are preserved in concurrent transactions) Avoidance of deadlock Transparency Concealing the heterogeneous and distributed nature of the system so that it appears to the user like one system

27. Copyrights @ 2006-7, Aatif Kamal27 Challenges : Transparency Access transparency: enables local and remote resources to be accessed using identical operations. Location transparency: enables resources to be accessed without knowledge of their location. 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.

28. Copyrights @ 2006-7, Aatif Kamal28 Assignment 1Linux system installation 2From the text book answer (Reading 1.3) 1.7 1.8 1.9 3Write a small article on history of distributed computing (2 pages max.)