Distributed Systems

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Distributed Systems

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Instructor

• Eng. Mohammad Sharaf
• Email sharaf_at_najah.edu

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Course Summary

• This course is intended to apply Java to
  distributed programming.
• The course will consist of
• Java as the language for building distributed
  applications.

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Java, a general-purpose OOP language

• Java is a great advance over C as a general
  purpose object oriented programming language.
• Java is a much easier language to learn than
  C.
• Java has shed the enormous burden imposed by C
  on the developer in the form of memory
  management.

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Prerequisites

• There are no formal prerequisites for this
  course, but there are some requirements of common
  sense.
• Prior knowledge of OOP, OS and NWs is a decided
  advantage

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Requirements

• Three home works.
• 3 home works will be devoted to modeling an ATM
  (standing for "automatic teller machine", not the
  network protocol called "asynchronous transfer
  mode").
• Term project, the ATM problems will use your Java
  knowledge for building a distributed system, in
  which the bank and the ATM are remote from one
  another.

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Requirements (CONT)

• No particular hardware or software platform is
  required. You must have a computing environment.
  You don't even need a network, since your
  processes can all be on one machine, connected by
  network protocol to your "localhost."

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Text Books

• Recommended books, you might even consider doing
  without a textbook and relying instead on the
  tutorials available from Sun's website.
• Core Java 2, Vol. I Fundamentals Horstmann,
  Cornell. Prentice Hall, 2002. ISBN 0130471771.
• Sun tutorials

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Text Books (CONT)

• The Java doc pages for Java. Java itself has
  such a web of pages describing all the classes
  that make up the standard Java libraries.
• For Part II, Distributed Programming
• Advanced Java Networking, Dick Steflik, Prshant
  Sridharan, Prentice Hall (www.phptr.com) ISBN
  0-13-084466-7
• Core Java 2, Volume II Advanced Features, 5th
  Edition, Cay Horstmann, Gary Cornell, 1998, ISBN
  1-56592-206-9.Core Java 2, Vol. II

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Software

• There is no specific requirement for software in
  this course. One needs a Java computing
  environment, of course, which means a version of
  the JDK (Java Developers Kit).
• To establish a computing environment it makes
  sense to use an IDE (Integrated Development
  Environment). There are several in wide use,
  including J-Builder from Inprise (formally
  Borland), and Visual Age from IBM.

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Software (CONT)

• Three products bear mention
• JBuilder from Borland, free home trial,
  bothersome registration required.
• Visual Cafe Standard Edition 4.1 It's free if you
  are brave enough to give them marketing
  information.
• NetBeans NetBeans is a modular, standards-based
  integrated development environment (IDE), written
  in Java.
• Sun Microsystems has released its own IDE
• Forte For Java. The Community edition is free

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The contents grouped in sections

• Java
• Threads
• Characterization of Distributed Systems
• Introduction
• Examples of Distributed Systems
• System Models
• Architectural Models
• Fundamental Models
• Distributed Computing
• Remote Method Invocation (RMI).
• Common Object Request Broker Architecture
  (CORBA)
• Internet security

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Evaluation

• 30 -- Homework and Programming Assignment
• 20 -- Term Project and class participation
• 20 -- Quizzes and Class participation
• 30 -- final exam

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Distributed system, distributed computing

• Early computing was performed on a single
  processor. Uni-processor computing can be called
  centralized computing.
• A distributed system is a collection of
  independent computers, interconnected via a
  network, capable of collaborating on a task.
• Distributed computing is computing performed in a
  distributed system.

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Distributed Systems
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Examples of Distributed systems

• Network of workstations (NOW) a group of
  networked personal workstations connected to one
  or more server machines.
• The Internet
• An intranet a network of computers and
  workstations within an organization, segregated
  from the Internet via a protective device (a
  firewall).

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Example of a large-scale distributed system
eBay (Source Los Angeles Times.)
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An example small-scale distributed system
(Source Los Angeles Times.)
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Computers in a Distributed System

• Workstations computers used by end-users to
  perform computing
• Server machines computers which provide
  resources and services
• Personal Assistance Devices handheld computers
  connected to the system via a wireless
  communication link.

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Centralized vs. Distributed Computing
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Monolithic mainframe applications vs. distributed
applicationsbased on http//www.inprise.com/visibr
oker/papers/distributed/wp.html

• The monolithic mainframe application
  architecture
• Separate, single-function applications, such as
  order-entry or billing
• Applications cannot share data or other resources
• Developers must create multiple instances of the
  same functionality (service).
• Proprietary (user) interfaces
• The distributed application architecture
• Integrated applications
• Applications can share resources
• A single instance of functionality (service) can
  be reused.
• Common user interfaces

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Evolution of paradigms

• Client-server Socket API, remote method
  invocation
• Distributed objects
• Object broker CORBA
• Network service Jini
• Object space JavaSpaces
• Mobile agents
• Message oriented middleware (MOM) Java Message
  Service
• Collaborative applications

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Why distributed computing?

• Economics distributed systems allow the pooling
  of resources, including CPU cycles, data storage,
  input/output devices, and services.
• Reliability a distributed system allow
  replication of resources and/or services, thus
  reducing service outage due to failures.
• The Internet has become a universal platform for
  distributed computing.

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The Weaknesses and Strengths of Distributed
Computing

• In any form of computing, there is always a
  tradeoff in advantages and disadvantages
• Some of the reasons for the popularity of
  distributed computing
• The affordability of computers and availability
  of network access
• Resource sharing
• Scalability
• Fault Tolerance

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The Weaknesses and Strengths of Distributed
Computing

• The disadvantages of distributed computing
• Multiple Points of Failures the failure of one
  or more participating computers, or one or more
  network links, can spell trouble.
• Security Concerns In a distributed system, there
  are more opportunities for unauthorized attack.

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Distributed Computing and Three-Tiered
Architecture

• A distributed application consists of
  collaborating objects residing on separate nodes
  of a network.
• The application, considered as a whole, is the
  sum total of the running processes that
  participate in providing the services of the
  application, where the processes are distributed
  across multiple machines connected by a network.

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Distributed Computing and Three-Tiered
Architecture (cont)

• RMI (Remote Method Invocation) is a facility for
  accessing remote objects, i.e. objects living in
  other Java virtual machines, typically on other
  (actual) machines.
• CORBA (Common Object Request Broker Architecture)
  is a standard architecture for distributed object
  collaboration, together with a standard
  communication protocol for inter object
  communication,
• that enables remote-object-access in a
  language-independent way.

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Distributed Computing and Three-Tiered
Architecture (cont)

• DCOM (Distributed Component Object Model) is a
  protocol that enables software components to
  communicate directly over a network in a
  reliable, secure, and efficient manner.