Path-Based Multicast Communication in Wormhole-Routed Unidirectional Torus Networks

This paper addresses the problem of one-to-many, or multicast, communication in wormhole-routed, n-dimensional torus networks. The proposed methods are designed for systems that support intermediate reception, which permits multi-destination messages to be pipelined through several nodes, depositing a copy at each node. A key issue in the design of such systems is the routing function, which must support both unicast and multicast traac while preventing deadlock among messages. An eecient, deadlock-free routing function is developed and used as a basis for a family of multicast algorithms. The S-torus multicast algorithm uses a single multi-destination message to perform an arbitrary multicast operation. The M-torus algorithm is a generalized multi-phase multicast algorithm, in which a combination of multi-destination messages is used to perform a multicast in one or more communication steps. Two speciic instances of the M-torus algorithm, the M d-torus and M u-torus multicast algorithms, are presented. These algorithms produce contention-free multicast operations and are deadlock-free under all combinations of network traac. A simulation study compares the performance of the diierent multicast algorithms, and implementation issues are discussed. The results of this research are applicable to the design of architectures for both wormhole-routed massively parallel computers and high-speed local area networks with wormhole-routed switch fabrics.