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Introduction to Multicast Route Construction

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• Most commonly used to "price" the cost of a multicast tree:
  • Each edge has a "cost" and the best multicast tree has the smallest total costs (of the edges in the tree)
  • Each edge has a cost and the best multicast tree has the smallest total cost from the source to any muticast destination.

• The two cost are different:

• Minimum total cost multicast tree:

• Minimum cost from source to any multicast destination:

  This type of multicast trees is usually called "minimum delay" trees or "Shortest Path Trees" (SPT).

• The problem of finding the minimum cost multicast tree is known as the minimum Steiner tree problem and it is NP-complete

  We will not discuss Steiner trees because

  • This is not a class on computer algorithms
  • more importantly, none of the existing multicast route construction algorithm uses Steiner trees...

• You will see that in both types of multicast tree forwarding algorithm, some form of minimum delay tree will be used.