# Greening the NetFPGA Reference Router
## 1 Introduction  
In information and communications technology (ICT) networks, the traditional design of network devices tends to primarily emphasize performance in terms of working speed. Power consumption, while given some attention, failed to be recognized as an important part of a family of design metrics, along with performance, reliability, security, etc. There are approximately one billion Ethernet connections all over the world [1]. The network devices were designed to translate improvements in digital circuits and operating frequency into performance, such as maximizing the router capacity at the cost of the highest and constant power consumption regardless of the traffic load. The energy efficiency of ICT systems has now been universally recognized as an important factor motivated by economics and environment issues [2]. With the sharp increase in Internet traffic, broadband accesses, complex services and end users, power consumption in the ICT industry is increasing exponentially at an alarming rate. A detailed report [3] estimated that a huge increase in overall network power consumption is predicted for European ISPs from around 21.4 terawatt-hours (TWh) in 2010 to around 35.8 TWh in 2020, if no green technologies are adopted. Such a huge increase in power consumption could result in billions in energy costs. On the other hand, carbon dioxide (CO\({}_{2}\)) emissions from the ICT industry should never be ignored [4]. In 2010, a study [5] indicated that the ICT industry contributed about 2% of global CO\({}_{2}\) emissions, which is equivalent to the entire airline industry. Many approaches have been proposed to make ICT systems more energy efficient [6; 7]. The majority of these proposed approaches can be divided into two categories: power scaling and sleepmode [8; 9; 10]. In the power scaling category, dynamic frequency scaling (DFS) offers an elegant solution for improving the energy efficiency of routers [11]. In this paper, an energy-efficient frequency-scaled router (FSR) with five different operating frequencies is implemented on the NetFPGA 1G board. The FSR is based on the modification of the NetFPGA reference router [12]. The NetFPGA is used because it is supported by a community of open source hardware and software and because of its modular structure in the reference pipeline, which provides a fast way to develop and experiment on custom green mechanisms. Data plane power consumptions of the FSR at different operating frequencies are measured. Control policies governing the dynamic frequency scaling of the FSR are also discussed. The power savings are achieved at the cost of transition time overhead (e.g., packet loss and delay during frequency transitions). To minimize the transition overhead, the control policies are directly implemented in hardware, which reduces the transition time by more than 80% compared to a software implementation. Experiments using real traffic traces indicate that, with dynamic frequency scaling, the FSR can reduce power consumption by 10% compared to the reference router. When the FSR is used in conjunction with green traffic engineering and Ethernet port shut-down (which is not a core part of the work), results show that up to 46% of data plane power consumption can be saved while providing the required quality of service. A new project entry for the frequency-scaled router has been created in the NetFPGA GitHub repository [13]. The research carried out in this paper was part of the European FP7 low Energy COnsumption NETworks (ECONET) project, which has resulted in the European Telecommunications Standards Institute (ETSI) Standard 203-237 [14]. The rest of this paper is organized as follows. Section 2 reviews the related work. Section 3 presents the design and architecture of the reference router (RR) and the frequency-scaled router (FSR). Section 4 describes different frequency control policies adopted in the FSR for dynamic frequency scaling.