Trade Offs in the Design of a Router with Both Guaranteed and Best-Effort Services for Networks on Chip (Extended Version)

Managing the complexity of designing chips containing billions of transistors requires decoupling computation from communication. For the communication, scalable and compositional interconnects, such as networks on chip (NoC), must be used. In this paper we show that guaranteed services are essential in achieving this decoupling. Guarantees typically come at the cost of lower resource utilization. To avoid this, they must be used in combination with best-effort services. The key element of our NoC is a router consisting conceptually of two parts: the socalled guaranteed throughput (GT) and best-effort (BE) routers. We combine the GT and BE router architectures in an efficient implementation by sharing resources. We show the trade offs between hardware complexity and efficiency of the combined router, and motivate our choices. Our reasoning for the trade offs is validated with a prototype router implementation. We show a lay-out of an input-queued wormhole 5× 5 router with an aggregate bandwidth of 80 Gbit/s. It occupies 0.26 mm in CMOS12. This shows that our router provides high performance at reasonable cost, bringing NoCs one step closer.