Issues and Prospects for Energy Saving Networks(Invited Paper)

Seung Hyun Jeon, Hyeontaek Oh, Hyunho Lee, Junkyun Choi†

Department of Electrical Engineering

KAIST

Daejeon, Republic of Korea

{creemur, hyeontaek, hyunho.lee}@kaist.ac.kr, jkchoi@ee.kaist.ac.kr†

Abstract—Studies on existing and future networks aimed atbuilding an energy saving networks have been conducted byglobal standard groups such as GreenTouch, IETF, and ITU-T. Future networks deployed without considering energy issueswill encounter major problems related to network maintenanceand operating costs, and ICT has been a recent area of interestwith respect to saving energy. Sensor networks/ad hoc networkshave been studied for a number of years in efforts to overcomebattery constraints. Meanwhile, research on reducing the overallenergy dissipation at the network level has been conducted byGreenTouch. In this paper, we introduce research issues andprospects for energy saving networks.

Index Terms—Energy saving network, 5G, Energy measure-ment, GreenTouch

I. INTRODUCTION

Energy saving issues have recently been explored in variousareas [1], [2]. In particular, current wired and wireless networkarchitectures that improve throughput without reducing energyconsumption for network equipment have been studied. How-ever, wireless sensor networks (WSNs) and ad hoc networkshave been studied in relation to energy savings to prolong acluster’s lifetime, which is largely dictated by battery limits[3]. Contention-free based and contention based MACs havebeen developed over the past one decade [4], [5]. Presently,prospective 5G technology based on ad hoc network usinga multiple-input multiple-output (MIMO) antenna is beingstudied.

Energy management and measurement also are importantissues in relation to energy saving networks. Standard ac-tivities such as IETF EMAN and ATIS are leading energymanagement and measurement groups [6], [7]. Currently,GreenTouchTMand ITU-T are considering all of the relatedenergy saving networks for wired and wireless networks [8]–[11]. Energy saving networks have been studied via locallydecentralized research through existing wired and wirelessnetworks. GreenTouchTMis playing an important role in in-tegrating energy savings into future networks.

The remainder of this paper is organized as follows: wediscuss related works in Section II. We suggest research issuesand approaches in order to establish an energy saving networkin Section III. Finally, we conclude the work in Section IV.

II. RELATED WORKS

Various researches for energy savings have been conductedover a long period of time. Prior works have dealt with energyissues within a homogeneous network such as a WSN, anad hoc network, and energy management for wired networks.

However, recent works have discussed global collaborationfor building energy saving networks and reducing energyconsumption based on wired and wireless networks [1], [2].

A. Energy efficiency of communication media

Energy used in delivering the user Internet today approx-imately accounts for 0.5 percent of typical national energyconsumption [12], [13]. Likewise, energy efficiency of anetwork has become an important topic recently. J. Baligaissued a paper on energy consumption and related efficiencyin various communication media [14]. This paper analyzesenergy consumption of wired and wireless access networks.It mainly focuses on the energy consumption of digitalsubscriber line (DSL), hybrid fiber coaxial (HFC) networks,passive optical networks (PONs), fiber to the node (FTTN),point-to-point optical (PtP) systems, WiMAX, and UniversalMobile Telecommunications System (UMTS) using widebandcode-division multiple access (W-CDMA). Energy efficienciesfor groups using fiber (PtP, PON) are much better than that ofgroups using copper and coaxial cable (DSL, HFC, FTTN).The former shows efficient power consumption at high accessrates. On the other hand, groups using copper and coaxialcable do not show high access rates or adequate efficiencycompared to their power supply. Wireless groups (WiMAX,UMTS) show exponential growth of power consumption astheir access rate rises.

B. Energy measurement protocol for wired network energyconsumption

Simple network management protocol (SNMP), proposedby IETF, is a management protocol for network equipment inan application layer [15]. However, while SNMPv1, SNMPv2,and SNMPv3 are currently available for standards, the energyprofile at the management information base (MIB) is notconsidered. In [16], the authors proposed an open standardprotocol for measuring energy using SNMP, which embracesenergyMeterMIB and energyMeterEvents with a MIB tree.

C. 1G/2G/3G/4G

Wireless mobile communication networks have experiencedfour generations of change. The first generation (1G) wirelessmobile communication network was an analog system thatwas used for public voice service with speed up to 2.4Kbps.The second generation (2G) was based on digital technologyand network infrastructure. 2G wireless systems supported amaximum data rate of 21.4Kbps. The goal of third generation

201978-1-4673-4828-7/12/$31.00 ©20122 IEEE ICTC 2012

Fig. 1. Heterogeneous network deployment, consisting of micro-/pico-cells,and femto-cells [17].

(3G) wireless systems was to provide wireless data servicewith data rates of 144Kbps to 384Kbps in wide coverage areas,and 2Mbps in local coverage areas. Recently developed fourthgeneration (4G) wireless technology provides data service withspeed up to 100Mbps with full-mobility, and 1Gbps with low-mobility. Thus far, each generation concentrated on improvingcommunication speed and supporting mobility. However, fornext generation communication networks, energy efficiencyshould also be considered as an important criterion.

D. Energy-aware methods for wireless communicationsOn the network level, the potential for reducing energy

consumption lies in the layout of networks [17]. Cell size incellular networks is in general fixed based on the estimatedtraffic load. The energy consumption for maintaining networkoperation has to be evaluated as a function of cell size. Hetero-geneous networks with a hierarchical mix of base stations withdifferent cell sizes have recently attracted increasing interestfor 4G mobile communication systems [18].

In heterogeneous networks, illustrated in figure 1, low powernodes complement the conventional macro-cellular networklayout, micro-/pico-cells cover high traffic demand areas,and indoor base stations constitute femto-cells that providebroadband coverage to indoor users. Furthermore, relay nodesare a cost efficient means to extend outdoor coverage, sinceexpensive backhaul links are avoided. Such heterogeneousnetworks potentially promise energy saving, because theyshorten the propagation distance between nodes, and therebyreduce the required transmission power.

On the other hand, deployment with only small cells maybe uneconomical, due to the prohibitive number of low power,and therefore short range, base stations. In addition, thisincreases the number of base stations operating at low loads,which may degrade the overall energy efficiency. Hence, foreach application heterogeneous deployments with an optimalbalance of macro-, micro-, pico-, and femto-cells must befound for the most energy efficient network layout.

E. Energy saving approaches in ad hoc networkMany studies on energy saving in WSNs have been con-

ducted the strong dependence on battery lifetime [3]. In thecase of an ad hoc network, the realization of sensor networksit is necessary to consider several constraints such as topologychange and power consumption. A power aware MAC for thead hoc network has been studied for a long time [4]. The power

aware MAC offers power management and control. Poweraware medium access control with signaling (PAMAS) savespower of nodes by turning off without reducing throughputwhen transmitting and receiving nodes are not active. Dynamicpower saving mechanism (DPSM) provides a more effectivepower saving mechanism than IEEE 802.11 distributed coordi-nation function (DCF), since the sender and receiver nodes gointo sleep state modes after packet transmission. Power controlmedium access control (PCM) considers maximum power forRTS/CTS packets and minimum power for data/ACK packets.In wireless ad hoc networks with beamforming antennas, di-rectional MAC with power control (DMAP) uses the intendedreceiver’s power control factor to calculate the transmit powersent to the source node [5].

III. ISSUES AND APPROACHES

In this section, we discuss open issues and approachesfor establishing an energy saving network. The followingexplanation is based on global standards except for 5G.

A. Energy Management

Energy management is becoming an additional requirementfor network management systems due to several factors includ-ing rising and fluctuating energy costs, increased awareness ofthe ecological impact of operating networks and devices, andthe regulations of governments on energy consumption andproduction.

The basic objective of energy management is to operatecommunication networks and other equipments with a minimalamount of energy while still providing sufficient performanceto meet service level objectives. A discussion of detailedrequirements has started in the IETF through Operations andManagement Area Working Group (OPSAWG), but for furtherexploration of this issued the IETF Energy Management(EMAN) working group has been established [6].

The IETF EMAN has focused on developing a new frame-work for energy management. In conventional energy manage-ment systems, energy consumption of a device is measuredby system itself. However, IETF EMAN takes a differentapproach – energy consumption of a device is reported bya different system. For this goal, the IETF EMAN workinggroup is currently working on the management of energy-aware devices, covered by the following items:

• Requirements for energy management• Energy management framework• Energy-aware Networks and Devices MIB documents• Power and Energy Monitoring MIB document• Battery MIB document• Applicability statement

B. Energy Measurement

Measurement for power savings is an important issue. Thefollowing standard activities pursue methods to define energyefficiency through energy measurement of network equipment.

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1) ATIS: The Alliance for Telecommunication IndustrySolutions (ATIS) [7] is a standards organization that developstechnical and operational standards for the telecommunicationindustry. It has more than 250 member companies, includ-ing various telecommunications service providers, equipmentmanufacturers, and vendors.

ATIS released standard documents about energy effi-ciency for telecommunication equipment in July 2009. ATIS-0600015.2009 [19] series provide a set of definitions, require-ments, and guidelines for calculating the TelecommunicationsEnergy Efficiency Ratio (TEER) of a system. These documentsalso provide standardized definitions of operational data ratesand conditions to be used when calculating the TEER of anygiven configuration.

TEER is defined as the ratio of maximum demonstratedthroughput (Td) to weighted power (energy consumption rate)Pw:

T EER =Td

Pw

where Td = Maximum Demonstrated Throughput, and Pw =Weighted Power (energy consumption rate).

Weighted energy consumption is calculated with the follow-ing formula:

Pw = a∗Pu1 +b∗Pu2 + c∗Pu3

where Pw = Weighted Power, (a,b,c) = weighting for power ateach utilization level, where a+b+c=1.0, (Pu1,Pu2,Pu3) = Powerat system utilization level.

The traffic profile, weights (a,b,c), and system utilizationlevels (u1,u2,u3) vary according to equipment class and posi-tion in the network. In [20], TEER calculation parameters forvarious network equipments are well defined. In figure 2, weshow that the power consumption of a DASAN V2624G (L2switch) is measured in a stand–alone manner based on [20]. Atthe left and right of figure 2, 2 ports and 12 ports are partiallyactive states. A packet size (66 bytes) at the right of figure2 includes header sizes (2 bytes) for user datagram protocol(UDP). Here, (a,b,c) is equal to (0.1,0.8,0.1) like [20]. Thepacket size, port state such as idle/on/off are important factorsto be considered for energy measurement.

2) ECR Initiative: Energy Consumption Rating (ECR) Ini-tiative [21] defines a framework for first-order approximationof energy efficiency for packet-based network and telecommu-nication equipments. Various aspects of operation are covered,including peak efficiency, variable-load efficiency and idle(statically configurable) energy efficiency. The latest versionof the draft was published in December 2010 [22].

ECR Initiative defines energy efficiency as energy consump-tion normalized to effective throughput. In other words, itdefines a more energy-efficient network system as one that cantransport more data (in bits) using the same energy budget (inJoules). In detail, ECR is normalized to W/Gbps and has aphysical meaning of energy consumption to move one gigabitworth of lie-level data per second. ECR typically reflects thebest possible platform performance within a set of hardwareand software features. ECR is defined as follow:

ECR =E100

Tf

Fig. 2. Example of power consumption for L2 switch.

where Tf = maximum throughput (Gbps), E100 = energyconsumption (watts).

3) ITU-T SG5 and SG13: ITU-T SG5 L.m&m (energyefficiency metric & measurement for telecom equipment)contains energy efficiency metrics and measurement methodsfor network equipment [8]. Draft recommendation L.m&mproposed EER (energy efficiency rating) as weighted, load-proportional metric, which is based on TEER from ATIS[19]. Ericsson, Huawei, Juniper network, Cisco, and NTT arepresently interested in ITU-T SG5. Recently, L.m&m infra(energy efficiency measures and measurement for telecommu-nication infrastructure) was proposed by China [9].

On the other hand, ITU-T SG13 Y.EnergyMRM (energymeasurement of networks) was proposed by Korea [10]. Con-sidering various input parameters such as traffic load, tem-perature/humidity, and time/status, energy/power consumptionmetrics for a network level are presented.

C. Recent Standard Activities

1) GreenTouchTM: GreenTouchTMis a consortium of theICT industry, academic and non-governmental research expertsdedicated to fundamentally transforming communications anddata networks, including the Internet, and significantly re-ducing the carbon footprint of ICT devices, platforms andnetworks [11]. The goal of the GreenTouchTMconsortium isto deliver the architecture, specifications, and road map –and demonstrate key components– needed to increase networkenergy efficiency by a factor of 1000 from current levels.

As a significant step forward on the road to realizing itsthousand-fold network energy efficiency improvement vision,GreenTouchTMdemonstrated a Large-Scale Antenna Systemproof of concept in February 2011 – this antenna system offersthe potential for tremendous energy savings because of itsnovel wireless transmission techniques.

In late March 2012, GreenTouchTMdemonstrated a newtechnology that will dramatically reduce energy consumptionin fiber-to-the-home (FTTH) networks. Called Bit-InterleavedPassive Optical Network (Bi-PON) technology, it will enable a30-fold power reduction relative to current technologies whileimproving performance and reducing cost [23].

2) Separation of data and signaling in a mobile network:Separation of the mobile network was recently announced

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Fig. 3. Data and signaling network operation [24].

through GreenTouchTM [24]. The proposal for an independentsignaling network is an efficient approach to achieve energysavings. Since this makes it possible to turn off an access pointof the area where no active user exists, it can reduce energydissipation for signaling. This new architecture assumes thatwidened coverage is provided for controlling access points.Figure 3 shows data and signaling network operation. Thesechallenges remain valuable as the new architecture for energysaving network.

3) Next generation communication (5G): Current 4G stan-dards such as Long Term Evolution (LTE)-Advanced andWiMAX 2 do not consider reducing energy consumption [2].In particular, the MIMO technique increases energy dissipationdirectly proportional to throughput due to the processing com-plexity for multiplexing gain and diversity gain. Hence, energyissues for mobile users and base stations remain challenges tobe solved. Presently, Beyond 4G such as 802.11ac is beingstudied to achieve capacity of more than 10 times than that ofthe existing LTE.

However, even though 5G is not defined yet, it is requiredto achieve higher performance for user’s traffic, devices, andenergy efficiency relative to 4G. In [25], the authors show thatif a large ad hoc network for all users on the entire bandwidthis built, the spectral efficiency actually increases linearlywith the number of users. On an information-theoretic basis,hierarchical cooperation (HC) based MIMO technologies con-sidering throughput as well as energy savings are currentlybeing studied. In detail, contention-free and contention-basedenergy efficient MAC designs on ad hoc networks still remainchallenges.

IV. CONCLUSION

Recent energy saving issues in ICT are prospective area ofresearches. This paper discusses open issues and approachesfor building an energy saving network in the future. On thewired network side, energy management and measurement forstandard activities have been studied. On the wireless networkside, 5G design as the next generation standard should considerreducing energy consumption. Currently, GreenTouchTMandITU-T are the most intensive activities for research relatedto energy saving networks.

ACKNOWLEDGMENT

This work was partly supported by the IT R&D programof MKE/KEIT [10039160, Research on Core Technologiesfor Self Management of Energy Consumption in Wired andWireless Networks] and the KCC(Korea CommunicationsCommission), Korea, under the R&D program supervised bythe KCA(Korea Communications Agency)”(KCA-12-911-04-001)

REFERENCES

[1] A. P. Bianzino, C. V. Chaudet, D. Rossi, J. Rougier ”A Survey of GreenNetworking Research,” IEEE Communications Surveys & Tutorials, vol.14, no. 1, pp. 2-20, 1st Quarter 2012.

[2] X. Wang, A. V. Vasilakos, M. Chen, Y. Liu, T. T. Kwon, ”A Survey ofGreen Mobile Networks: Opportunities and Challenges,” Springer MobileNetwork and Application, vol. 17, no. 1, pp. 4-20, Feb. 2012.

[3] I. Akiyldiz, W. Su, Y. Sankarasubramaniam, and E. Cayirci, ”A surveyon sensor networks,” IEEE Communications Magazine, vol. 40, no. 8,pp. 102-114, Aug. 2002.

[4] S. Kumar, V. S. Raghavan, J. Deng, ”Medium Access Control protocolsfor ad hoc wireless networks: a survey,” Elsevier Ad Hoc Networks, vol.4, no. 3, pp. 326-358, May 2006.

[5] O. Bazan, M. Jaseemuddin, ”A Survey On MAC Protocols for WirelessAd hoc Networks with Beamforming Antennas,” IEEE CommunicationsSurveys & Tutorials, vol. 14, no. 2, pp. 216-239, 2nd Quarter 2012.

[6] IETF EMAN, http://datatracker.ietf.org/wg/eman/charter/[7] ATIS, http://www.atis.org/[8] ITU-T Q17/SG5 Draft Recommendation L.m&m TD-1054rev4,

http://www.itu.int/ITU-T/meetingdocs/index.asp[9] ITU-T Q17/SG5 proposal L.m&m infra C-417, Sep. 2012,

http://www.itu.int/ITU-T/meetingdocs/index.asp[10] ITU-T Q12/SG13 Draft Recommendation Y.EnergyMRM TD-366, Sep.

2012, http://www.itu.int/ITU-T/meetingdocs/index.asp[11] GreenTouchTM, http://www.greentouch.org/[12] J. Baliga, R. Ayre, K. Hinton, W.V. Sorin, and R.S. Tucker, ”Energy

Consumption in Optical IP Networks,” Journal of Lightwave Techonology,vol. 27, no. 13, pp. 2391-2403, July 2009.

[13] R.S. Tucker, R. Parthiban, J. Baliga, K. Hinton, R.W.A. Ayre, and W.V.Sorin,”Evolution of WDM Optical IP Networks: A Cost and EnergyPerspective,”, Journal of Lightwave Technology, vol. 27, no. 3, pp. 243-252, Feb. 2009.

[14] J. Baliga, R. Ayre, K. Hinton, and R.S. Tucker, ”Energy consumption inWired and wireless aceess networks”, IEEE Communications Magazine,vol. 49, no. 6, pp. 70-77, June 2011.

[15] RFC 1157, A Simple Network Management Protocol (SNMP),http://tools.ietf.org/pdf/rfc1157.pdf

[16] S. S. Chavan, S. Jayaprakash, and V. J. Kumar, ”An Open StandardProtocol for Networking of Energy Meters,” IEEE Transactions on PowerDelivery, vol. 23, no. 4, pp. 1749-1753, Oct. 2008.

[17] L. M. Correia, D. Zeller, O. Blume, D. Ferling, Y. Jading, I. Godor, G.Auer, L. V. der Perre, ”Challenges and Enabling Technologies for EnergyAware Mobile Radio Networks”, IEEE Communications Magazine, pp.66-72, Nov. 2010.

[18] H. Claussen, L. Ho, and F. Pivit, Effects of Joint Macrocell andResidential Picocell Deployment on the Network Energy Efficiency, Proc.19th IEEE PIMRC 08, Cannes, France, Sept. 2008.

[19] ATIS-0600015.2009, ”Energy Efficiency for Telecommunication Equip-ment: Methodology for Measurement and Reporting – General Require-ments”, Feb. 2009.

[20] ATIS-0600015.03.2009, ”Energy Efficiency for TelecommunicationEquipment: Methodology for Measurement and Reporting for Router andEthernet Switch Products”, Jul. 2009.

[21] ECR Initiative, http://www.ecrinitiative.org/[22] ECR draft 3.0.1, ”Network and Telecom Equipment–Energy and Perfor-

mance Assessment”, Dec. 2010.[23] Bi-PON, http://www.greentouch.org/index.php?page=Bi-PON[24] A. Capone, A. F. d. Santos, I. Filippini, B. Gloss, ”Looking Beyond

Green Cellular Networks,” IEEE 9th Annual Conference on Wireless On-Demand Network Systems and Services (WONS), pp. 127-130, Jan. 2012.

[25] A. Ozgur, O. Leveque, D. N. C. Tse, ”Hierarchical Cooperation AchievesOptimal Capacity Scaling in Ad Hoc Networks,” IEEE Transactions onInformation Theory, vol. 53, no. 10, pp. 3549-3572, Oct. 2007.

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