Adaptive fault-tolerant deadlock-free routing in meshes and hypercubes

We present an adaptive deadlock-free routing algorithm which decomposes a given network into two virtual interconnection networks, VIN/sub 1/ and VIN/sub 2/. VIN/sub 1/ supports deterministic deadlock-free routing, and VIN/sub 2/ supports fully-adaptive routing. Whenever a channel in VIN/sub 1/ or VIN/sub 2/ is available, it can be used to route a message. Each node is identified to be in one of three states: safe, unsafe, and faulty. The unsafe state is used for deadlock-free routing, and an unsafe node can still send and receive messages. When nodes become faulty/unsafe, some channels in VIN/sub 2/ around the faulty/unsafe nodes are used as the detours of those channels in VIN/sub 1/ passing through the faulty/unsafe nodes, i.e., the adaptability in VIN/sub 2/ is transformed to support fault-tolerant deadlock-free routing. Using information on the state of each node's neighbors, we have developed an adaptive fault-tolerant deadlock-free routing scheme for n-dimensional meshes and hypercubes with only two virtual channels per physical link. In an n-dimensional hypercube, any pattern of faulty nodes can be tolerated as long as the number of faulty nodes is no more than [n/2]. The maximum number of faulty nodes that can be tolerated is 2/sup n-1/, which occurs when all faulty nodes can be encompassed in an (n-1)-cube. In an n-dimensional mesh, we use a more general fault model, called a disconnected rectangular block. Any arbitrary pattern of faulty nodes can be modeled as a rectangular block after finding both unsafe and disabled nodes (which are then treated as faulty nodes). This concept can also be applied to k-ary n-cubes with four virtual channels, two in VIN/sub 1/ and the other two in VIN/sub 2/. Finally, we present simulation results for both hypercubes and 2-dimensional meshes by using various workloads and fault patterns.