CTIS 490 DISTRIBUTED SYSTEMS

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CTIS 490DISTRIBUTED SYSTEMS

• WEEK 2
• DISTRIBUTED SYSTEMS
• ARCHITECTURES

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INTRODUCTION

• Distributed systems are complex pieces of
  software where components are dispersed across
  multiple machines.
• It is crucial that these systems are properly
  organized.
• There has to be a distinction between the logical
  organization of the collection of software
  components and the actual physical realization.

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SOFTWARE ARCHITECTURES

• A component is defined as a modular unit with
  well defined interfaces that is replaceable
  within its environment.
• A connector is described as a mechanism that
  mediates communication, coordination, or
  cooperation among components.
• Using components and connectors, we can classify
  various distributed architectural styles.

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SYSTEM ARCHITECTURES

• Basically, software architectures can be realized
  in two ways
• Centralized Architectures
• Decentralized Architectures

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CENTRALIZED SYSTEM ARCHITECTURES

• A server is a process implementing a specific
  service, for example a file system service or a
  database service.
• A client is a process that requests a service
  from a server by sending it a request and
  subsequently waiting for the servers reply.

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APPLICATION LAYERING

• In general, a client-server architecture has
  three logical layers
• The user-interface level
• The business/processing level
• The data level

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EXAMPLE INTERNET SEARCH ENGINE APPLICATION
LAYERING
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MULTITIERED ARCHITECTURES

• How do we distribute a three level client-server
  application on the physical machines?
• The simplest organization is to have only two
  types of machines
• A client machine containing only the programs
  implementing the user-interface level.
• A server machine containing the rest, that is the
  programs implementing the processing and data
  level.

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CLIENT-SERVER ORGANIZATIONS

• Thin clients-----------------------------------Fat
  clients

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DECENTRALIZED SYSTEM ARCHITECTURES

• A decentralized architecture is a peer-to-peer
  (P2P) system which use the computing power and
  bandwidth of the participants in the network.
• This model differs from the client-server model
  where communication is usually to and from a
  central server.
• P2P systems represent a paradigm for construction
  of distributed systems and applications in which
  data and computational resources are contributed
  by many hosts on the network (Intranet or
  Internet).
• P2P refers to a class of systems and applications
  that employ distributed resources to perform a
  function in a decentralized manner.

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APPLICATIONS OF PEER-TO-PEER SYSTEMS

• File sharing (music, video, etc.)
• Examples Napster, Gnutella, Freenet, and KaZaA
• Process sharing (data analysis, scientific
  computing, etc.)
• Examples SETI_at_Home
• Collaborative environments (instant messaging,
  teleconferencing, etc.)
• Examples Microsoft Meeting and Yahoo Messenger

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CLASSIFICATION OF PEER-TO-PEER SYSTEMS

• Hybrid Peer-to-Peer Systems
• Has a central server that keeps information on
  peers and responds to requests for that
  information.
• Pure Peer-to-Peer Systems
• A pure P2P network does not have the notion of
  clients or servers, but only equal peer nodes
  that simultaneously function as both clients and
  servers to the other nodes on the network.