Lecture 2

• Lecture 2
  • Video
  • Summary
  • Topics of today
  • Why Distributed System
  • Real time distributed system
  • Process Models / Distribute computations
  • Network Topologies
  • Synchronization

Video

link

Summary

• criteria a distributed system specifies
  • multiple processes must be present
    • these should be sequential
    • each having independent thread of control
    • processes can be both - user or system processes
  • IPC - Inter Process Communication
    • processes should communicate with each other using msgs
    • msgs take some finite time depending upon channel (can be wired/ wireless)
  • Disjoint Address space
    • so shared memory multi-processor system ko we do not count as distributed system
  • Collective Goal
    • OLX - Auction eg

Topics of today

• Introduction contd..

Why Distributed System

• In real life, we mostly have geographically distributed environments
  • Banking me ATMs are geographically dispersed
• Speedup
  • Traditional uniprocessor models have reached already their speedup
  • parallel processing helps to improve it, but not much scalable
  • so shift to Distributed systems
  • can incrementally increase computing power by purchasing resources
• Resource Sharing
• Fault Tolerance : TMR
  • Graceful degradation
• Examples
  • Data intensive applications
  • Compute intensive applications
    • use client, server architecture
  • World wide web
  • social networks - fb, insta
  • inter-bank n/ws
  • peer-to-peer networks
    • internet telepony, content distribution, file distribution
    • Napster used it to distribute songs
      • still it is not a truly P2P bcz it used a centralized directory
    • Gnutellr, Kazza - avoided use of central directory
    • OCEAN STORE project
      • hosted at University of California, Berkeley
      • they built an online archiving mechanism on top of P2P, known as Tapestry
    • Skype

Real time distributed system

• Industrial plants use these extensively for their network of controllers which control their diff mechanical systems and machineries

Process Models / Distribute computations

• model = an abstraction of real life thing
  • physical level details are exluded
• Common Knowledge of a process
  • no process has complete view of the DS
    • n/w topology
    • global state
  • processor will know
    • its own identity
    • its neighbors
    • size of the network
    • rest info it ill acquire over time by polling

Network Topologies

• ring
• tree
• hypercube
• linear

Synchronization

• clock issues