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Data structure used/maintained by the Distance Vector Routing Algorithm

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• Data Structures used in the Routers:
  • Each node (router) maintains two data structures:

    A routing table containing entries of the form: A distance table with the following structure:

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• The distance to a destination node
  • The distance to a destination node:

    Distance to a (destination) node x = the smallest of the distances in the distance table that that (destination) node x

    Example:

    Sample distance table: Then: Distance to C = 2 Other distances: Distance to A = 1 Distance to B = 2 Distance to E = 3 ....

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  • A more sublte example:

    Suppose a node G has the following distance table entry: Distance table of a node G: Dest | Via D Via F -------+--------------------- .... | ... ... F | 5 7 .... | ... ... Question: What is the distance from G to F ? Answer: distance(G,F) = min( 5, 7 ) = 5 Example with a full network (to provide context):

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• Relationship of the Routing table and Distance table
  • Fact:

    The routing table can be constructed using the information in the distance table (So we do not need to maintained the Routing table explicitly)

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  • How to construct the Routing table using the Distance table:

    for ( each destination D ) { Find the smallest distance to D in the Distance table The neighbor used to reach D is the "next node" in the routing table }

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  • Example:

    Example of a distance table entry: Notice that: Smallest distance to destination F is via the neighbor node D The Routing table of node G will be like this: Dest Next hop ---------+------------ ... | ..... F | D ... | .....

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• My combined distance and routing table
  • Dictactical note:

    In the presentation of the Distance Vector algorithm, I combine the distance table and the routing table into a single table

    Example:

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• Initializing the data structures
  • Example network:

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  • Initialization at node A:

    Node A is only aware of the link cost to its immediate neighbors: Therefore, the distance vector is initialzed as follows: Note: Initially, the node G is not in the distance table !!! I include every destination in the tables because it's easier to make the figures !!! The routing table is initialized as follows:

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• Other relevant information (used by Distance Vector Algorithm)
  • Other information:

    Distance from the (computing) node to all its neighbors

    Note:

    "Distance" a neighbor node = delay to the neighbor node (The node can measure the queueing delay and transmission delay as discussed previously)