As the network size increases, traditional approaches to multicasting such as distance-vector and shortest-path-first routing demand more bandwidth, memory, and processing resources at each router. A proposed architecture, called core based tree (CBT), overcomes these problems by building only one tree per multicast group. The CBT approach, however, does not route packets through the shortest possible path. This paper presents a modification to the CBT tree building algorithm so that minimal spanning trees are built when needed and packets are routed through nearly optimal paths. We also give a procedure to choose the core of the tree thus built and this, in turn, helps reduce the multicast delay. Examples, using SURAnet topology, are solved to illustrate our approach.
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