Presented by Jinghai Rao

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Introduction to distributed multimedia

• Presented by Jinghai Rao
• Nov. 8th, 2000

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Introduction

• This book is particularly interested in the
  demands imposed by multimedia computing.
• The book also evaluates the requirements imposed
  by multimedia computing and proposes and approach
  to open distributed processing.
• This chapter introduces the field by considering
  the emergence of cistributed systems and open
  distributed processing, and then considering the
  particular requirements of multimedia and the
  consequent challenge.

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What is a distributed system

• A distributed system is a system designed to
  support the development of applications and
  services which can exploit a physical
  architecture consisting of muliple, autonomous
  processing elements that do not share primary
  memory but cooperate by sending asynchronous
  messages over a communications network.

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The advantages of distributed systems

• Resource sharing
• Availability
• Extensibility
• Performance
• Distributed organizations

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Problems introduced by a distributed environment

• A bad definition by Leslie Lamport
• A distributed system is one that stops you
  getting any work done when a machine youve never
  even heard of crashes.

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Problems introduced by a distributed environment

• Services can be accessed concurrently by a number
  of different client applications.(conflict)
• Distributed systems are quite different from
  standalone machines in that partial failure can
  occur.(lack of information on the cause of
  failure)
• Difficulties also exist in locating the right
  server in a distributed environment.(migration)
• Servers might be replicated to enhance
  availability.(consistency)

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Problems introduced by a distributed environment

• It would be undesirable if the application
  programmer had to deal with the problems when
  developing distributed programs.
• Most systems provide a level of distribution
  transparency to the programmer.
• That will carry a performance overhead in
  accessing servers.
• Modern thinking is to provide selective
  transparency, where the application programmer
  can specify the required level of transparency.

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Important trends in distributed processing

• Distributed systems are likely to be very large.
  It is crucial that the techniques adopted in
  distributed systems platforms scale to larger
  configurations.
• There is growing pressure for a convergence
  between distributed systems and
  telecommunications architectures.
• Distributed systems are becoming more
  heterogeneous in that the individual components
  are likely to vary greatly across the glocal
  system.

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Focus on heterogeneity

• Heterogeneous hardware
• Heterogeneous platforms
• Heterogeneous languages
• Heterogeneous management policies

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The goal of open distributed processing

• In simple terms, the goal of open distributed
  processing is to enable interaction with services
  from anywhere is the distributed environment
  without concern with services from anywhere in
  the distributed environment without concern for
  the underlying environment.

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The goal of open distributed processing

• A crucial part of open distributed processing is
  the definition of conformance testing procedures
  to ensure that different implementations by
  different manufacturers adhere to the
  standardized interfaces.
• Interoperability
• Portability

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The goal of open distributed processing

• The goal of open distributed processing is not
  only to standardize the highest level interfaces
  it is also seen as crucial to have a complete
  architecture where the individual components are
  themselves open.
• Advantages
• The benefits of interoperability and portability
  extend to all components in teh architecture.
• The architecture can be specialized or can evolve
  by changing the implementation of individual
  components.
• The architecture can be extended by introducing
  new components at a later date

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The different levels of openness
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Solving the problem of heterogeneity

• Network and machine independence is achieved by
  providing abstractions over the characteristics
  of the underlying physical environment.
• For platform independence, its necessary to have
  a set of agreed abstractions over system
  resources .
• To achieve language independence, its necessary
  to provide abstractions over the interfaces
  offered by different languages so that they can
  interwork.
• To heterogeneous management policies, its
  necessary to provide a meta-architecture for
  management.

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The role of standards

• International agreement and high level of
  confidence in the agreement.
• Two styles of standards organization
• International treaty-based, such as ISO, ITU.
• Industrial consortia, such as OSF, OMG.
• Alternatively, achieving a certain level of
  market penetration IBM-compatible PC, SUN Java.

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Standards organizations and open distributed
processing

• ISO/ITU-T reference model for open distributed
  processing (RM-ODP).
• OMG common object request broker architecture
  (CORBA).
• The open groups distributed computing
  environment (DCE).

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Introducing multimedia

• Media
• The term media refers to the storage,
  transmission, interchange, presentation,
  representation and perception of different
  information types, such as text, graphics, voice,
  audio and video.
• Multimedia
• The term multimedia is to denote the property of
  handling a variety of representation media in an
  integrated manner.

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The motivation of distributed multimedia systems

• There is an end user demand for systems which
  achieve better integration of a wide variety of
  media types.
• The technology is emerging to support multimedia
  computing
• End user pull
• Technology push

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Continuous and discrete media types.

• Continuous media
• Items of data must be presented according to
  particular real-time constraints for a particular
  length of time.
• Discrete media
• No temporal dimension.

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Assessment of the demands of digital media
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Compression
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The challenge

• Support for continuous media
• Quality of service management
• Real-time synchronization
• Multiparty communication

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summary

• This chapter has provided an initial introduction
  of multimedia on the field of open distributed
  processing.
• The first part of this chapter considered the
  topic of open distributed processing.
• The second part of the chapter then charted the
  emergence of multimedia.