Question 1

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Question 1
2013-04-29 11:10:53

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  1. Define and discuss the overlay network.
    • An overlay network is a computer network which is built
    • on top of another network. Nodes in the overlay can be thought of as being
    • connected by virtual or logical links, each of which corresponds to a path,
    • perhaps through many physical links, in the underlying network.

    • The problem is that we are dealing only with logical
    • paths. It may very well be the case that two nodes A and B which are neighbours
    • in the overlay network are physically placed far apart. As a consequence, the
    • logically short path between A and B may require routing a message along a very
    • long path in the underlying physical network.
  2. Describe stateful and stateless servers.
    • “A stateless server does not keep
    • information on the state of its clients, and can change its own state without
    • having to inform any client”

    • —For instance a Web
    • server is stateless. It records some info but if this information is lost, it
    • will not lead to a disruption of the service

    • “A stateful server generally
    • maintains persistent information on its clients.”

    • —A file server must
    • maintain a table with files and permissions
  3. Describe and compare different architectural styles.
    • layered style:
    • components are organised in a layered fashion where a component at layer
    • Li  is allowed to call components at the
    • underlying layer Li-1, but not the other way around;

    • object-based architectures:  each object corresponds to what we have
    • defined as a component, and these components are connected through a (remote)
    • procedure call mechanism;

    • Data-centred architectures:  evolve around the idea that processes
    • communicate through a common (passive or active) repository;

    • event-based architectures:  processes essentially communicate through the
    • propagation of events, which optionally also carry data;

    • shared data spaces:  Event-based architectures combined with
    • data-centred architectures;