Distributed Systems Concepts and Design the 3rd Edition

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Distributed Systems Concepts and Designthe 3rd
Edition

• Wonkwang University
• Computer and Information Communication Engg
• Prof. Su-Chong Joo
• scjoo_at_wonkwang.ac.kr

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Lecture Organization

• Lectures Time Table
• Class 01(daytime)- Tue. 78 hours, Thur. 7
• Class 85(nighttime) Mon. 12, Wed. 1
• Lecture Class
• 3hrs/a week in selected lecture slots, plus more
  if requested
• Class Assessment
• 80 by exam (Mid 40, Final 40)
• 20 by reports and so on.

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Useful Information

• Textbook (essential)
• Coulouris et al, Distributed Systems Concepts
  and Design, 3rd edition, Addison-Wesley
  2001(?????? ??)
• Handouts
• printed copies of slides only
• see module web page and Cyber library
• Lecture webpage
• Homepages blue.wonkwang.ac.kr -gt
  lectures-gtdistributed systems
• Lecture notes, syllabus, handouts, BBS
• www.cdk3.net You can get all information
  about this book
• Give me comments/suggestions, anytime welcome!

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Distributed Systems

• Concurrency
• - No global clock
• - Independent failure

• Autonomous systems
• - Computer network
• - Distributed software

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Why Distributed Systems?

• Main features
• geographical distribution of autonomous computers
• communication through cable/fiber/wireless/...
  connections
• Distributed system ?
• A collection of independent computers that
  appears to its users as a single coherent system
  logically.
• Advantages
• interaction, co-operation, and sharing of
  resources
• Benefits
• reduced costs, improved availability and
  performance
• Scalability, resource sharing, fault tolerance.

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Lectures Aims

• Introduce the principles and concepts involved in
  design of distributed systems
• Familiarize with mechanisms and protocols for
  inter-process communication
• Give overview of fundamental problems and
  techniques for their solution

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Topics Covered in DS

• Architectures and models
• Inter-process communication
• Distributed objects and Invocations
• General Operating systems
• Distributed file storage
• Naming services
• Timing issues, co-ordination, concurrency control
  and transactions
• Security and fault-tolerance
• Distributed multimedia
• Distributed Programming and analyzing
• Socket, Java RMI, CORBA

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Distributed Systems

• Chapter 1 Overview of Distributed Systems

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This lecture Introduction of DS

• Definition of Distributed Systems
• A collection of independent computers that
  appears to its users as a single coherent system.
• A distributed system organized as
  middleware.Note that the middleware layer
  extends over multiple machines.

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This lecture Introduction of DS

• Examples
• Internet
• Intranets
• Mobile and ubiquitous computing
• World-Wide Web
• Characteristics
• Challenges

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Definition of DS

• Processes
• execute concurrently
• interact in order to co-operate to achieve a
  common goal
• co-ordinate their activities and exchange
  information by means of messages transferred over
  a communication network

A distributed system is a collection of
autonomous computers interconnected by a computer
network and equipped with distributed system
software to form an integrated computing
facility.
Data
Communication Network
Data
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Importance of Distributed Computing

• Distributed computer systems are critical for
  functioning of many organizations
• Banks Transport
  Telecommunications
• Distributed Application
• A set of processes that are distributed across a
  network of machines and work together as an
  ensemble to solve a common problem

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Typical examples

• Internet
• global network of interconnected computers which
  communicate through IP protocols
• Intranet
• a separately administered network with a boundary
  that allows to enforce local security policies
• Mobile and ubiquitous computing
• laptops, PDAs, mobile phones, printers, home
  devices, ...
• The World-Wide Web
• system for publishing and accessing resources and
  services across the Internet

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A typical portion of the Internet
intranet


ISP


backbone
satellite link
desktop computer
server
network link
ISP Internet service provider
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Characteristics of Internet

• very large and heterogeneous
• enables email, file transfer, multimedia
  communications, WWW,...
• open-ended
• connects intranets (via backbones) with home
  users (via modems, ISPs)

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A typical Intranet
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Characteristics of intranets

• several LANs linked by backbones
• enables info. flow within organization
• electronic data, documents,
• provides services
• email, file, print servers,...
• often connected to Internet via router
• in/out communications protected by firewall

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Portable and handheld devices
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Mobile ubiquitous computing

• Wireless LANs (WLANs)
• connectivity for portable devices (laptops, PDAs,
  mobile phones, video/dig. cameras, )
• WAP (Wireless Applications Protocol)
• Home intranet
• devices embedded in home appliances (hi-fi,
  washing machines, )
• universal remote control communication

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Web servers and web browsers
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WWW

• world-wide resource sharing over Internet
• based on technologies
• HTML (HyperText Markup Language)
• URL (Uniform Resource Locator)
• Client-Server architecture
• Open system
• Open-ended
• can be extended, re-implemented, ...

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Challenges posed by DSs

• Due to
• complexity
• size
• changing technologies
• societys dependence
• Challenges posed by DSs
• Heterogeneity(???)
• Openness(???)
• Security(???)
• Scalability(???)
• Fault handling(????)
• Concurrency(???, ???)
• Transparency(???)

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Heterogeneity

• varying software and hardware
• need for standards (protocols, middleware)
• mobile code support
• virtual machine (cf, Java)

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Openness

• independence of vendors
• publishable key interfaces
• CORBA
• publishable communication mechanisms
• Java RMI

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Security

• confidentiality (protect against disclosure)
• cf, medical records
• integrity (protect against alteration and
  interference)
• cf, financial data
• gt Need encryption and knowledge of identity.

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Scalability problem

• Examples of scalability limitations

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Scalability Techniques (1)

• The difference between letting
• a server or
• a client check forms as they are being filled

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Scalability Techniques (2)

• An example of dividing the DNS name space into
  zones

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Failure handling

• Ability to continue computation in the presence
  of failures.
• detect/mask/tolerate failures
• recovery from failures
• redundancy

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Concurrency

• Processes execute simultaneously and share
  resources.
• synchronization
• inter-process communication

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Transparency

• Concealment of the separated nature of system
  from user/programmer
• gtNetwork transparency
• Access transparency Location Transparency
• cf .log on, email on SoCS network
• Transparencies
• Access transparency
• Location transparency
• Concurrency transparency
• Replication transparency
• Failure transparency
• Mobile transparency(Migration transparency)
• Scaling transparency
• gt ANSA Reference Manual ISO Reference Model
  for Open Distributed Processing(RM-ODP)

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Transparency ctd

• 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.

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Transparency (Distributed Systems in Tanenbaum)
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Summary

• DSs
• pervasive in society
• use a variety of technologies
• understanding underlying concepts and issues
  important in their management, implementation,
  programming
• DSs challenges
• Heterogeneity(???)
• Openness(???)
• Security(???)
• Scalability(???)
• Fault handling(????)
• Concurrency(???, ???)
• Transparency(???)

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Overview of Internet Information Appliances
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Information Appliance Control Middleware
Home Server
Service Provider
Application
Appl.Manager
MiddleWare
Home Automation Control
JVM
LonWorks
RTOS
Home GW
HAVi
Service or Device Control Module
Home Theater
UPnP, Jini
Home Network
ADSL
PLC,1394, PNA, Ethernet Bluetooth, RF, IrDA,
802.11
Internet
Control panel
Control
Home Office
Control
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Mobile Collaboration for Information Appliance
Internet PC
PC
Home Server
1
DTV STB
2
3
HDD
MoCos Server
Mobile WhiteBd Chat
4
5
Mobile Instance Messaging
Collaborative Browsing
Secure P2P