# Greening the NetFPGA Reference Router
## 5 Experiments
### Fixed Traffic Experiments  
As indicated in Equation (1), the total power consumption of a router is affected by the operating frequency, the number of active ports, the traffic bit rate and the packet size. To evaluate the impact of each of these factors on the performance and power consumption of the RR and the FSR, a series of carefully designed experiments is conducted. We start with measuring the power consumption of the RR and the FSR in idle state when the board is configured as the RR or the FSR, but without routing any traffic. To evaluate the impact of the operating frequency and the number of active ports on the power consumption, the RR bit file and the FSR bit file are, in turn, downloaded into the core logic FPGA processor and configured as an RR and an FSR for comparison. The four Ethernet ports are activated one by one, and the power consumption of the RR and the FSR is measured at their allowed operating frequencies. The measurement results show that the power consumption of a router is proportional to the number of active ports, with approximately 1 W additional power consumption for each activated port. As shown in Tables 3 and 4, the results indicate that under the same operating frequencies of 125 MHz or 62.5 MHz, the FSR consumes more power than the RR. This is due to the fact that an additional AFIFO module and several frequency division modules are integrated into the FSR. Each additional module incurs additional power consumption. Moreover, for the RR, the two SRAMs work synchronously with the core logic FPGA processor for writing and reading data at 125 MHz or 62.5 MHz. For the FSR, the core logic can be scaled among five different frequencies of 125 MHz, 62.5 MHz, 31.3 MHz, 15.6 MHz and 7.8 MHz, but the two SRAMs are working asynchronously with the core logic and running at 125 MHz constantly. This means the power consumption difference between the RR and the FSR at 62.5 MHz is even more than that at 125 MHz, because at 62.5 MHz,the two SRAMs run at 62.5 MHz in the RR and run at 125 MHz in the FSR, although the core logic FPGA processor is running at the same 62.5 MHz. The traffic characteristics (traffic bit rate and packet size) could also affect the power consumption. As indicated in [14], the packet sizes of 64 Bytes, 576 Bytes and 1500 Bytes are typical packet sizes in real network links, and the packet size profile peaks at 64 bytes and 1500 bytes. The minimum size of a standard Ethernet packet is 64 bytes. One thousand five hundred bytes is the maximum transmission unit (MTU) for Ethernet. MTU is an important factor for network throughput and should be as large as possible, because larger MTU introduces less overhead for payload transmission. In multi-network environments, if a maximum-sized packet travels from a network with a larger MTU to a smaller MTU network, the packet will have to be fragmented to smaller-sized packets. Five hundred seventy six bytes is the default IP maximum datagram size. It is also the default conservative packet size that all IP routers support. To evaluate the impact of the traffic characteristics on the power consumption, a series of experiments were performed using different operating frequencies (125 MHz, 62.5 MHz, 31.3 MHz, 15.6 MHz and 7.8 MHz), different traffic bit rates (from 100 Mb/s to 1 Gb/s for each link) and different packet sizes (64 bytes, 576 bytes and 1500 bytes). Packet streams are sent from the four ports on the packet generator, routed through the four ports on the router and back to the corresponding ports on the packet generator. Figure 10 shows an example of the total power consumption of the RR and the FSR under the same 1500-byte packet stream with different operating frequencies and different aggregated input traffic bit rates. Experimental results indicate that power consumption is proportional to the traffic bit rate and the operating frequency for both the RR and the FSR.