Combining SDM-Based Circuit Switching with Packet Switching in a Router for On-Chip Networks

A Hybrid router architecture for Networks-on-Chip “NoC” is presented, it combines Spatial Division Multiplexing “SDM” based circuit switching and packet switching in order to efficiently and separately handle both streaming and best-effort traffic generated in real-time applications. Furthermore the SDM technique is combined with Time Division Multiplexing “TDM” technique in the circuit switching part in order to increase path diversity, thus improving throughput while sharing communication resources among multiple connections. Combining these two techniques allows mitigating the poor resource usage inherent to circuit switching. In this way Quality of Service “QoS” is easily provided for the streaming traffic through the circuit-switched sub-router while the packet-switched sub-router handles best-effort traffic. The proposed hybrid router architectures were synthesized, placed and routed on an FPGA. Results show that a practicable Network-on-Chip “NoC” can be built using the proposed router architectures. 7 × 7 mesh NoCs were simulated in SystemC. Simulation results show that the probability of establishing paths through the NoC increases with the number of sub-channels and has its highest value when combining SDM with TDM, thereby significantly reducing contention in the NoC. 1. Introduction Real-time applications have grown in complexity and require more and higher-power computing resources. These applications are then suitable to be run on parallel environments such as MultiProcessor Systems-on-Chip “MPSoC” platforms. However, application performance in an MPSoC platform strongly depends on the on-chip interconnection network used to carry communications between cores in the platform. Since Real-time applications generate both streaming and best-effort traffics, there is then a need for the on-chip interconnection network to provide QoS for the streaming traffic and data completion for the best-effort traffic. Streaming traffic is best handled in circuit-switched network. Since communication resources are prereserved before any data transfer, QoS is thereby intrinsically supported. Circuit switching often leads to a poor usage of communication resources, since reserved resources for a transaction are exclusively used by that transaction. For that reason, it is not suitable for best-effort traffic. Best-effort traffic is well handled in packet-switched network, however, because of its nondeterministic behavior; packet switching is not suitable for streaming traffic. To improve resource utilization in circuit-switched networks, time division