CS 775/875: Fall 2002

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CS 775/875 Fall 2002

• Chapter 2 System Models

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Introduction

• Architectural model defines the way in which the
  components of systems interact with one another
  and the way in which they are mapped onto an
  underlying network of computers.

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Architectural models

• Software layers (software architecture)
  services offered and requested between processes
  located in the same or different computers.
• Terminology Platform, middleware,
• The end-to-end argument

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System Architectures

• The division of responsibilities between system
  components and the placement of the components in
  the network
• Client-server model, multiple servers, proxy
  servers and caches, peer processes, mobile code,
  mobile agents, network computing, thin clients,
  spontaneous networking

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Design requirements for distributed architectures

• Performance issues---responsiveness, throughput,
  load balance
• Quality of service
• Use of caching and replication
• Dependability---fault tolerance and security

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Fundamental Models

• A system model has to describe the main
  entities, their interactions, and the
  characteristics that affect their behavior
• Aspects captured in these models Interaction,
  failure, security

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Interaction Model

• Why do processes interact?
• Performance of communication channels
• Computer clocks and timing events
• Synchronous (bounded time) versus asynchronous
  (unbounded time) distributed systems
• Event ordering and logical clocks

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Failure Model

• Omission and commission failures
• Byzantine failures versus fail-stop behavior
• Timing failures (relevant for synchronous)
• Masking failures
• Reliability of one-to-one communication

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Security Model

• Protecting objects
• Securing processes and their interactions
• The enemy Threats to processes( to servers and
  clients), threats to communication channels,
  denial of service
• Defeating security threats Cryptography,
  authentication, secure channels
• Denial of service and mobile code