Routers vs Switches, How Much More Power Do They Really Consume? A Datasheet Analysis Hakim Mellah and Brunilde Sans`o Electrical Engineering Department ´ Ecole Polytechnique de Montr´eal Montr´eal, Canada
[email protected],
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Abstract—This paper presents an analysis of a compiled database of power consumption and networking functionalities found in datasheets of routers and switches of some major manufacturers. We found very striking differences in consumption between switches and routers of the same nominal capacity. The paper analyzes the significance of such results and sheds some light on the most consuming elements and networking features that could be extremely useful in the re-planning and operation of energy-efficient networks. Keywords-Green Communications, Energy-Efficient Networks, Power Consumption, Routers and Switches.
I. I NTRODUCTION With the proliferation of Internet applications and devices and its adoption as the global information network, the amount of traffic flowing through the Internet has dramatically increased. Therefore, the power required for routing and processing Internet traffic has been growing accordingly [1], [2]. This situation has taken place in parallel with an ever growing concern for global warming and the need for energy conservation. The answer of the research community has been not only to improve the hardware consumption but also to find methods to design and operate networks in a more energy efficient way. Design models have traditionally been solely concerned with the trade-off of costs versus performance but recently there has been an increasing number of energy-aware design and operational methods aiming at managing or reducing Internet and ICT consumption [1]–[6]. A major difficulty for the assessment of the proposed and forecoming energy efficient planning methods is the lack of a standard set of data to characterize consumption. In some cases (see for instance [5], [7]), experiments are carried for a given set of equipments or overall estimates are proposed [6]. In other cases, assumptions are made based on practical knowledge that is well known to equipment manufacturers but that is not necessarily available to the general public. For instance, it is generally assumed that, given the reduced functionalities, switches consume less than routers, or that modular chassis devices consume more than fixed ones, however, to our knowledge, there has not been in the literature a systematic quantification of those differences. c 978-1-4577-0351-5/11/$26.00 2011 IEEE
To advance the field of energy efficient network planning and operation there is, therefore, an urgent need for the results of extensive and systematic testings of different types of devices and manufacturers so that the influences of their type, configuration and networking features in the overall power consumption are known. Given that such an extensive benchmarking is still not available and in order to set the basis for future testings, we searched for available public data on the power characteristics of two of the most popular networking devices: routers and switches. As a result, we created a database of 84 routers and 181 switches collected from datasheets and technical specifications of equipments1 . This paper has several objectives. First we want to set the basis for an evolving database that could be available for current and future studies in energy efficient networks. Second, we want to quantify through the database analysis the real extent of some known differences in consumption. Finally, we want to create awareness on the power consumption impact of networking functionalities and open the debate on the necessity of energy-hungry type of equipments versus the possibility of replacing them by more energy-wise ones. To reach such objectives, we have organized the material of the paper as follows. In Section II, we present a brief review of the articles that have dealt with device energy consumption and explain the issues concerning power measuring and energy proportionality. In Section III we explain how the database was built and present its major characteristics. The general differences between routers and switches are portrayed in Section IV. A power profiling of routers and switches based on different networking features is described in Section V. The differences in power consumption with respect to the type of network deployment (access, edge or core) are also underlined. The article concludes in Section VI.
1 Available
on request by writing to the second author.
II. E NERGY C ONSUMPTION A SSESSMENT A. Literature Review on Device Power Consumption There are few articles that deal specifically with device power consumption and, to our knowledge, there is no thorough compilation of data across different vendors and types of devices. The issue of energy consumption has been dealt with in an ad-hoc manner, presenting some wellknown facts in different papers (see the compilation provided in [2]). The profiling of server and datacenter power consumption can be found in different works such as [8]–[10]. For wireless devices, one has to mention the work presented in [11] where experiments were set for a single type of 802.11 device to allow for the creation of a set of empirical linear equations and the follow up work presented in [12] to use simulation for the assessment. Concerning IP wireline devices, a pioneering measurement study was done by the authors in [5] who performed experiments to evaluate the power consumption of the chassis and the cards of a few types of routers. More recently, one can mention the benchmarking framework proposed by the authors in [7] where the power consumption of seven different networking devices was evaluated. Let us also mention the ECR benchmarking initiative that is supported by several vendors and by Lawrence Berkeley Laboratory [13]. The above mentioned articles and reports deal with the empirical evaluation of the power consumption effect of different networking functionalities for a few type of devices or with how to do effective benchmarking. Unfortunately, none has reported a widespread analysis of a large set of different devices from different manufacturers. B. Nominal Power and Energy Proportionality Issues From the experimental data described in II-A, one can underline two key results: 1) That the nominal power of device plates does not correspond to the real power required for operation and 2) That power consumption does not present an energy proportional behavior. With respect to the first point, the tests carried out in the literature show indeed that for routers and switches the device plates overestimate the actual consumption by about 20 to 25%. This is due to the fact that manufacturers want to make sure that the power supplies bought by service providers for their equipment are suitable. The implication for this work is that the reader should be aware that the curves presented in the following sections do show a general trend but should ideally be corrected by a systematic benchmarking on all the devices. The second point refers to the fact that with current device technology the power is not proportional to the load and there is a significant power consumption for the idle
state. To account for the non-proportional behavior, the work done by the authors in [7] has recently proposed an energy proportionality index equal to one minus the ratio of idle versus maximum power consumption. Such a ratio should be an interesting measure to examine accross devices but, unfortunately, no information is given in datasheets about idle consumption. III. T HE DATABASE This section is devoted to the presentation of the database and some statistics about the type of equipment that has been chosen. A. Database Gathering The database presented in this paper has been collected from six major network equipment manufacturers. These vendors offer a wide range of equipment and their datasheets are publicly available on their websites. For each equipment, a set of information was recorded from its technical specification provided by the vendor, including the following: the maximum power consumption (in watts), the maximum capacity (in Giga-bit per second (Gbps)), the maximum throughput (in Mega Packet per seconds (Mpps)), the type of the chassis (fixed chassis or modular chassis), the physical dimensions and weight, the layer (for switches which are either layer 2 or layer 3), the type of available and supported network interfaces or ports (including Power over Ethernet (PoE), Ethernet, Gigabit Ethernet (GbE), 10-GbE, optical interfaces including small form-factor pluggable (SFP), 10GbE SFP (XFP), Optical Carriers (OC), SONET/SDH, etc..), the type of offered services, including Multiprotocol Label Switching (MPLS), layer 3 Virtual Private Network (VPN), Quality of Service (QoS), Security (such as firewall, detection and protection against attack and filtering capabilities), Reliability or availability (such as hardware redundancy, MPLS fast reroute and non-stop routing in failure events), Multicasting and other supported data transmission technologies such as Asynchronous Transfer Mode (ATM) and Packet over SONET (POS). In Table I the type and number of equipments collected from each vendor are summarized. A classification that may have an impact from a power consumption point of view is used: switches are layer 2 (L2), layer 3 (L3), fixed with PoE capabilities (FSP), fixed without PoE capabilities (FSNP) or modular (MS) whereas routers are classified as fixed (FR) or modular (MR). B. Provided Services Routers are, in general, used to connect to the outside networks (WAN, edge, metro and core networks) providing certain services such as QoS, security, MPLS, VPN, reliability and availability, multicasting and others. While these services are very limited in layer 2 switches, they are widely available in layer 3 switches.
Vendor Cisco Brocade Juniper Alaxala Nortel Allied Telesis Total
Total 50 41 19 33 26 12 181
L2 15 0 0 10 12 0 37
Switches L3 FSP 35 11 41 8 19 8 23 3 14 10 12 1 144 41
FSNP 29 26 9 20 16 8 108
MS 10 7 2 10 0 3 32
Total 22 16 25 11 6 4 84
Routers FR MR 0 22 8 8 0 25 4 7 2 4 0 4 14 70
Total 72 57 44 44 32 16 265
Table I: Type and number of equipment in our database
IV. ROUTERS AND S WITCHES : A P OWER C ONSUMPTION P ERSPECTIVE In this section we present the analysis on the database power consumption entries. Figure 1 shows the power over capacity ratio (in Watts/Gbps) plotted over the maximum capacity. In order to obtain a more precise idea on the power consumption trends of routers and switches, the linear regressions of each group of data are also shown. The reader should note that the axes are in logarithmic scale and that there is a large diversity in consumption values for the same level of capacity in either the switch or the router group. The second observation is that overall, switches seem to present a significant lower consumption than routers of the same capacity. In both cases, it is clear that power consumption increases with the capacity while the power consumption to capacity ratio decreases. This is a suggestive feature that ratifies a well-known fact that larger units tend to be more energyefficient which could lead to robustness shortcomings if a planner is tempted to address the design issues based solely on power efficiency (see [3]). Let us note again the importance of future benchmarking, as efficiency should be rather related to the actual power consumed at a given level of operation. From a power consumption perspective, routers can be divided into two large groups: fixed chassis and modular chassis routers. Fixed chassis routers consume less power, are compact and light-weight, but offer a limited set of services, a limited type of interfaces for connectivity and a limited range of capacities. Modular chassis routers, on the other hand, are flexible, scalable, offer more services and connectivity interfaces, but consume more power, are heavier and occupy more space.
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C. Available Interfaces It can be appreciated that while routers provide a variety of LAN and WAN interfaces ranging from Ethernet-based (FE, GbE, 10-GbE, SFP and XFP), ATM, Packet over SONET (POS) and high speed SONET (oc-48, oc-192 and oc-768), most switches are equipped with Ethernet-based interfaces only (since they were mainly designed to be used in LAN environments). This can have an impact on the choice of equipment and, therefore, on network overall consumption.
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Figure 1: Power consumption ratio of routers and switches
The same classification is also valid for switches. Moreover, fixed switches can be further subdivided into two subgroups, those with PoE (Power over Ethernet) ports and those without PoE ports. Figure 2 illustrates the power consumption ratio with their regressions for each of these groups. The figure shows that modular routers (MR) are the most power consuming equipment, followed by modular switches (MS) and then fixed switches with PoE ports (FSP). Fixed routers (FR) and fixed switches without PoE ports (FSNP) consume the least power among the groups, with FR consuming slightly more than FSNP. It is worth mentioning that the extra power consumed by PoE equipment is not really wasted. This power is used to power-up connected devices, such as IP telephones, video cameras and wireless LAN access points, through the Ethernet cable. Of course, a portion of this power is dissipated in the cable. For instance, a standard IEEE 802.3af-2003 port provides up to 15.4W of DC power to the connected device, from which 12.95 W (about 84%) is guaranteed to be available at the powered device.
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V. F URTHER A NALYSIS The analysis for the classification adopted in table I can be further refined by looking at the different characteristics of each group. A. Ratio of Power for Modular Chassis In modular chassis devices, a significant portion of the power is consumed by the basic system (cooling system, supervisor system, routing and forwarding system). We wanted to assess the ratio of consumption between the basic configuration (chassis empty) and the full loaded chassis. Unfortunately, such information was available only for few devices. We have found that the basic system may consume up to 58% of power of the fully loaded system. For the collected data, no less than 19% of the power is consumed by the basic system without doing any useful function. This waste of energy can be reduced if a proper power management strategy is adopted (see [2], [4], [14], [15]). B. Layer 2 vs. Layer 3 Switches While all routers operate at layer 3, switches can be either layer 2 or layer 3 devices. In general, layer 2 switches have fixed configuration and provide few connection interface types (mainly Ethernet, FE, SFP, GbE and 10-GbE) whereas layer 3 switches can have fixed or modular (chassis) configurations. Fig.3 depicts the power consumption ratio (W/Gbps) of layer 2 and layer 3 switches with fixed chassis and with or without PoE ports. In the legend, SL3PF and SL2PF indicate, respectively, layer 3 and 2 switches with PoE ports whereas SL3NPF and SL2NPF indicate, respectively, layer 3 and 2 switches without PoE ports. The figure shows that,
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Figure 3: Fixed Layer 2 and Layer 3 switches
in general, layer 2 switches have limited switching capacity and consume less power compared to layer 3 switches. It is also found that the PoE feature produces a larger difference in consumption than the layer in which the switch operates. C. Physical Specifications Physical specifications including physical dimensions, weight and type of physical connections and line-cards compatible with the equipment do also have a direct impact on the network power consumption. While fixed configuration devices are light and occupy a small space, chassis-based devices are heavy and need a large space (sometimes they need a specific cabinet or closet). It is worthmentioning that not only power but also volume increases with the device capacity. In terms of overall consumption, larger volumes may imply special spaces with more air-conditioning, thus indirectly adding extra consumption to the device power specification. D. Network Deployment In this section we analyze the equipment power consumption according to the part of the network where it is going to be deployed. Figure 4 illustrates the power consumption ratio of the access, edge and core routers and switches using the classification provided by their respective manufacturers. To have a fair comparison between these devices, only layer 3 switches without PoE capabilities have been considered. As expected, the figure shows that in the access network (see fig. 4(a)), switches are the dominant equipments, with a better power consumption to capacity ratio. In the edge (see fig. 4(b)), both type of devices are present, with routers spanning a larger capacity range and having a higher power consumption ratio than switches. In the core (see fig. 4(c)),
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In this paper we presented, for the first time, an extensive power consumption study of routers and switches across different type of devices and manufacturers based on public datasheets. Some of the results presented may have been known by equipment vendors but have not been previously reported in the literature. The most striking result of the study is the amount of difference in consumption found between switches and routers that can be literally of several orders of magnitude for devices of the same capacity. Other results were expected, but nonetheless interesting to present to the general public, given its importance in energy efficient network planning. For instance, the fact that modularity comes at a very much higher power expense than fixed devices and that the PoE feature is the one that consume the most but has a large potential for overall power savings. This can lead to a re-thinking of network planning as planners should be able to carefully decide if particular functionalities are really essential or just nice to have and if they are worth the significant energy consumption cost. We could gather little information on the time of release of each device because few manufacturers made it available in their datasheets. We believe that this is an important information that can be used to make longitudinal studies to evaluate the power performance improvements over time and should be systematically provided by the manufacturers. Another important information that should be available in datasheets is the ratio between peak power and idle power consumption to be able to extrapolate power efficiency values in operating conditions. Finally, we think that in order to design and operate more energy efficient networks, there should be a thorough benchmarking of the available equipments; we believe that the database study presented in this paper can help for future statistical comparisons. As a future work, we are studying the impact of the different components (such as chassis, supervisor board and line-cards) on the power consumption of the modular equipments.
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VI. C ONCLUSION AND F UTURE W ORK
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routers are the dominant equipments and also span over a wide range of capacities. There are only few core switches concentrated around a small capacity range, but still offering lower power consumption to capacity ratio. Overall, given the set of capacities and the differences in power consumption ratio, one can say that the edge is the part of the network where it would be very feasible and cost-effective in terms of power to consider the replacement of routers by switches.
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Figure 4: Power consumption ratio of Access, Edge and Core Routers and Switches
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