High-speed data paths in host-based routers

In networking today, host workstations are increasingly being used as routers. Host based routers offer a number of advantages, but they suffer from inefficient support for high bandwidth interfaces. The authors' work has focused on the technology's major drawback its inefficiency in supporting high bandwidth interfaces. Their approach is to optimize packet processing by applying techniques that transfer packets directly among host interfaces, thus removing an extra data copy. This technique increases data throughput by 45 percent while reducing the host's CPU load. They found that peer DMA forwarding can increase host based router throughput by up to 45 percent, supporting bandwidths of 480 Mbps. Peer DMA host based forwarding requires network interface cards with substantial shared memory resources, because packet queues are stored on the interfaces themselves, rather than in host RAM. The queuing algorithm remains in the host CPU, supporting advanced queue management. Current systems have limited packet processing. A combination of streamlined forwarding algorithms and aggregate interrupt processing should further increase host based capability. Moving some of the IP processing out to the NIC coprocessor may enable this. It is also apparent that as processor speeds increase, the advantages of peer DMA will aid throughput for small packet sizes.