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Link Failures and Route change

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• Link/node failures
  • Detection of a link/node failure:

    A link or node failure will result in unacknowleged data frames

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  • What to do in case of a link/node failure:

    The link cost to the failed node is set to infinity (To avoid using that transmission link/node)

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• Link failure and the Centralized (link state) algorithm
  • How the centralized algorithm handles link/node failures:

    Nodes must periodically broadcast (flood) their link state (costs) information to all nodes in the network (To recompute the shortest paths due to changing queueing delays) When a link/node fails, the link cost will be set to infinity

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  • Result:

    The failed links/nodes will have infinite cost in the next round of broadcast/flood messages So the failed links/nodes will be excluded from the shortest paths in the next round of computation

    The Dijkstra's Algorithm will not used links with infinite costs and the failed link is avoided

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• Link failure on the Decentralized (Bellman/Ford) Distance Vector algorithm
  • Fact:

    A failed link/node can change the (minimum) distance to a destination

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  • Recall that:

    When the (minimum) distance to a destination changes: The node must schedule/send a distance vector update message to all its neighbor nodes (containing the new (minimum) distance)

    Result:

    The distant vector update message (containing the new distance value) will be processed by the neighbor nodes The processing can trigger more distance vector messages.

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  • Fact:

    There are a number of interesting phenomenons in the route update procedure in the Distance Vector algorithm

    That's why I want to do another complete example...