A comparison of router architectures for virtual cut-through and wormhole switching in a NOW environment

Most commercial routers designed for networks of workstations (NOWs) implement wormhole switching. However wormhole switching is not well suited for NOWs. The long wires required in this environment lead to large buffers to prevent buffer overflow during flow control signaling. Moreover, wire length is limited by buffer size. Virtual cut-through (VCT) achieves a higher throughput than wormhole switching. Moreover, the traditional disadvantages of VCT switching, as buffer requirements and packetizing overhead, disappear in NOWs. In this paper, we show that VCT routers can be simpler than wormhole ones, while still achieving the advantages of using virtual channels and adaptive routing. We also propose a fully adaptive routing algorithm for VCT switching in NOWs. Moreover, we show that VCT routers outperform wormhole routers in a NOW environment at a lower cost.