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A technique to enhance multicomputer routers for faulttolerant routing with modest increase in routing complexity and resource requirements is described. This method handles solid faults in meshes, which includes all convex faults and many practical nonconvex faults, for example, faults in the shape of L or T. As examples of the proposed method, adaptive and nonadaptive faulttolerant routing algorithms using four virtual channels per physical channel are described.

We show that deadlocks due to dependencies on consumption channels are a fundamental problem in wormhole multicast routing. This type of resource deadlocks has not been addressed in many previously proposed wormhole multicast algorithms. We also show that deadlocks on consumption channels can be avoided by using multiple classes of consumption channels and restricting the use of consumption channels by multicast messages. We provide upper bounds for the number of consumption channels required to avoid deadlocks. In addition, we present a new multicast routing algorithm, column-path, which is based on the well-known dimension-order routing used in many multicomputers and multiprocessors. Therefore, this algorithm could be implemented in existing multicomputers with simple changes to the hardware. Using simulations, we compare the performance of the proposed column-path algorithm with the previously proposed Hamiltonian-path-based multipath and an e-cube-based multicast routing algorithms. Our results show that for multicast traffic, the column-path routing offers higher throughputs, while the multipath algorithm offers lower message latencies. Another result of our study is that the commonly implemented simplistic scheme of sending one copy of a multicast message to each of its destinations exhibits good performance provided the number of destinations is small.

We examine the performance of the TCP protocol for bulkdata transfers in mobile ad hoc networks (MANETs). We vary the number of TCP connections and compare the performances of three recently proposed on-demand (AODV and DSR) and adaptive proactive (ADV) routing algorithms. It has been shown in the literature that the congestion control mechanism of TCP reacts adversely to packet losses due to temporarily broken routes in wireless networks. So, we propose a simple heuristic, called fixed RTO, to distinguish between route loss and network congestion and thereby improve the performance of the routing algorithms. Using the ns-2 simulator, we evaluate the performances of the three routing algorithms with the standard TCP Reno protocol and Reno with fixed RTO. Our results indicate that the proactive ADV algorithm performs well under a variety of conditions and that the fixed RTO technique improves the performances of the two on-demand algorithms significantly.

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