# Greening the NetFPGA Reference Router
## 5 Experiments
### Evaluation Metrics  
_Power consumption_: Power consumption in a network device is the sum of two components: quiescent power and dynamic power. Quiescent power is the static power drawn by the device when it is powered up, configured with user logic, but there is no traffic load. Dynamic power is the power consumed during processing traffic load in the core or I/O of the device, and it is, therefore, frequency dependent. The total power consumption of a network device can be modelled as a linear function of the traffic characteristics as given in Equation (1) [29]:  
\[P_{t}=P_{q}+P_{d}=P_{q}+ACfV^{2} \tag{1}\]  
where \(P_{t}\) is the total power, \(P_{q}\) is the quiescent power, \(P_{d}\) is the dynamic power, \(A\) is the activity factor, such as the fraction of the circuit that is switching, \(C\) is the load capacitance, \(f\) is the core operating frequency and \(V\) is the supply voltage. For a given NetFPGA board, \(P_{q}\), \(C\) and \(V\) are fixed values, and \(A\) is affected by the number of active ports, the instantaneous traffic bit rate and the forwarding packet size. The power Equation (1) is the guideline for the theoretical analysis. In operation, the NetFPGA 1G board is a PCI-based board, and all of the power supplies are derived from the 3.3-V and the 5-V power rails on the PCI bus. The embedded FPGA chips draw power from the 3.3-V rail of the PCI bus, and the PHY components are supplied by the 5-V rail. The 3.3-V and 5-V pins of the PCI bus extender are used to measure the overall current drawn by the 3.3-V and 5-V powered components on the NetFPGA board mounted on the PCI bus extender. Hence, the total power consumption can be calculated with Equation (2):  
\[P_{t}=I_{3.3}\times 3.3+I_{5}\times 5 \tag{2}\]  
where \(P_{t}\) is the total power, \(I_{3.3}\) is the total current of the board components' drawn power from the 3.3-V rail of the PCI bus and \(I_{5}\) is the total current of 5-V powered components. Figure 9: Lab setup. _Performance_: The peak measured throughput is the peak measured rate of successful data delivery over a real implemented system. In the performance evaluation, it is the most important metric to be measured because it directly determines the preset threshold in the frequency control policies. Each operating frequency has an associated traffic throughput threshold beyond which the router will begin to lose a significant number of packets. The peak measured throughput must be measured as accurately as possible. Otherwise, the difference between the input traffic load and inaccurate preset threshold could degrade the performance of the FSR. The round trip time (RTT) is also an important network performance measure in the performance evaluation. It is the propagation time taken for a packet to travel from a specific source to a specific destination and return back to the source. Measuring the RTT assists network operators and end users in understanding the network performance and taking measures to improve the QoS if needed. To ensure the required QoS, a router should speedily and accurately forward data packets with little or no packet loss. Packet loss is another important metric adopted in the performance evaluation in the experiments. In the NetFPGA user data path pipeline, packet loss occurs in four MAC receive queues and four MAC output queues, but not in any MAC transmit queues. This is because the transmit queues simply take packets from the corresponding output queues and send the packets out through the Ethernet ports. Thus, the total packet loss can be calculated with the following equation:  
\[L_{t}=L_{r}+L_{o} \tag{3}\]  
where \(L_{t}\) is the total packet loss, \(L_{r}\) is the total packet loss in the four receive queues and \(L_{o}\) is the total packet loss in the four output queues. Transition time is closely associated with packet loss. It is the time required for the router to switch from one frequency to another.