spanning tree

Hi all,
in the pix, a: a network, b: a spanning tree for leftmost router, c : a multicast tree for group 1, d: a multicast tree for group 2.

can you help me to derive algrogithm or pseudocode how to come up with b and c. Tks.

spanning-tree.png
BeginToLearnAsked:
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Infinity08Commented:
The spanning tree (b) can be obtained with Dijkstra's shortest path algorithm (like I mentioned in your previous question).

The last two tree's are simply sub-tree's of the spanning tree, so only the required nodes are connected (ie. those nodes that are part of the multicast group). They could be obtained simply by starting from the end of every branch, and removing edges that are not needed.
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BeginToLearnAuthor Commented:
i wonder one thing. They never mention the source and destination. So how can we apply shortest path algorithm?
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Infinity08Commented:
You said yourself that the trees were "for leftmost router". So, that's the destination in all three trees.

Dijkstra's algorithm finds the shortest paths between all sources and that destination.
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BeginToLearnAuthor Commented:
"for the leftmost router" is the term  from the book hihi
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Infinity08Commented:
Either way - it answers your question about what the destination is ;)
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