A method for routing packets across multiple paths in NoCs with in-order delivery and fault-tolerance gaurantees

Abstract

Networks on Chips (NoCs) are required to tackle the increasing delay and poor scalability issues of bus-based communication architectures. Many of today's NoC designs are based on single path routing. By utilizing multiple paths for routing, congestion in the network is reduced significantly, which translates to improved network performance or reduced network bandwidth requirements and power consumption. Multiple paths can also be utilized to achieve spatial redundancy, which helps in achieving tolerance against faults or errors in the NoC. A major problem with multipath routing is that packets can reach the destination in an out-of-order fashion, while many applications require in-order packet delivery. In this work, we present a multipath routing strategy that guarantees in-order packet delivery for NoCs. It is based on the idea of routing packets on partially nonintersecting paths and rebuilding packet order at path reconvergent nodes. We present a design methodology that uses the routing strategy to optimally spread the traffic in the NoC to minimize the network bandwidth needs and power consumption. We also integrate support for tolerance against transient and permanent failures in the NoC links in the methodology by utilizing spatial and temporal redundancy for transporting packets. Our experimental studies show large reduction in network bandwidth requirements (36.86% on average) and power consumption (30.51% on average) compared to single-path systems. The area overhead of the proposed scheme is small (a modest 5% increase in network area). Hence, it is practical to be used in the on-chip domain.