Multicast in Wormhole-Switched Torus Networks Using Edge-Disjoint Spanning Trees

A tree-based multicast algorithm for wormhole-switched networks which makes use of multiple edge-disjoint spanning trees is presented. The disjoint spanning-tree multicast, or DSTM, algorithm provides deadlock-free multicast routing that is fully compatible with unicast. Application of the DSTM algorithm to 2-dimensional torus networks is considered. A family of constructions of two spanning trees in the torus is given along with a formal proof of their edge-disjointness. Two constructions from this family are selected and shown to produce diameters no greater than twice that of the torus. Flit-level simulation results are presented to show that DSTM outperforms the best single spanning tree multicast approach by up to a factor of two. The DSTM algorithm is also simulated for different spanning tree constructions. The results show that our novel tree construction is significantly better for multicast than those produced by a general tree construction method that applies to arbitrary-topology networks [16]. Finally, two approaches to providing single link fault tolerance with DSTM are presented and evaluated.