Seminar 3

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Seminar 3
2013-04-29 12:54:50

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  1. What is the di erence between a vertical distribution and a horizontal dis-tribution?
    Vertical distribution refers to the distribution of the di erent layers in amultitiered architectures across multiple machines. In principle, each layer isimplemented on a di erent machine. Horizontal distribution deals with thedistribution of a single layer across multiple machines, such as distributinga single database.
  2. In a structured overlay network, messages are routed according to the topol-ogy of the overlay. What is an important disadvantage of this approach?
    The problem is that we are dealing only with logical paths. It may verywell be the case that two nodes A and B which are neighbors in the overlaynetwork are physically placed far apart. As a consequence, the logicallyshort path between A and B may require routing a message along a verylong path in the underlying physical network.
  3. Give a compelling (technical) argument why the tit-for-tat policy (i.e., a lecan be downloaded only when the downloading client is providing contentto someone else) as used in BitTorrent is far from optimal for le sharing inthe Internet.
    The reasoning is relatively simple. Most BitTorrent clients are operatedbehind asymmetric links such as provided by ADSL or cable modems. Ingeneral, clients are o ered a high incoming bandwidth capacity, but no onereally expects that clients have services to o er. BitTorrent does not makethis assumption, and turns clients into collaborative servers. Having sym-metric connections is then a much better match for the tit-for-tat policy.