Dynamic Link Control with Changing Trafficfor Power Saving
Yutaka Fukuda, Takeshi Ikenaga, Hitomi Tamura, Masato Uchida, Kenji Kawahara, and Yuji Oie
Network Design Research CenterKyushu Institute of Technology
Kawazu 680-4, Iizuka 820-8502 Japan.
{ytk, ike, tamu, m.uchida, kawahara, oie}@ndrc.kyutech.ac.jp
Abstract—The scope of this proposal is greening technology ina network area. Our major purpose in this study is to develop amethod for achieving power conservation with a network itself.
One of the effective ways for power conservation is to have anetwork switch which can adapt its processing speed to arrival
traffic rate just as Intel’s Speedstep technology [4], because
existing switches fully work regardless of a traffic amount. We
first confirm that whether the difference in transmission capacity
influences the power consumption at switch, and show that a
Giga bit Ethernet port consumes 2 or 3 W with an addition ofa link. Therefore, we can conclude that the dynamic control fortransmission capacity with traffic volume is one of the importantand effective ways to reduce the power consumption in a network.
Based on this consideration, we propose a scheme to achieve thedynamic control of the transmission capacity between switches inorder to reduce the power consumption, based upon the change
in traffic volume. In this context, Link Aggregation is used to
dynamically and gradually control the transmission speed. As forthe demo system, Ethernet Bonding (trunking) technology is used
to form a single logical link. Two PCs, which emulate the network
switch, dynamically control the number of links according withthe changing arrival traffic. This demo is intended to explicitly
show the possibility of power conservation with a network itself
by adapting the transmission capacity to arrival traffic.
Index Terms—Power saving, Link aggregation, IEEE 802.3ad,Link Aggregation Control Protocol

I. I NTRODUCTION
The scope of this proposal is greening technology in anetwork area. Previous studies showed that the energy consumption by Internet devices in the U.S. increased more than
threefold from 2000 to 2006 [1], [2]. Furthermore, Cisco Systems forecasted that global IP traffic would increase fivefold
from 2008 to 2013 [3]. In order to accommodate this growing
IP traffic, the increase of power consumption in a network
area is expected. Therefore, our major purpose is to develop
a method for achieving power conservation with a network
itself.
One of the effective ways for power conservation is to havea network switch which can adapt its processing speed toarrival traffic rate just as Intel’s Speedstep technology [4],because existing switches fully work regardless of a traffic
amount. In this context, we first confirm whether the differencein transmission capacity influences the power consumption
at switch. We connect two switches by a UTP cable, add
links between switches one by one, and measure the power
consumption in each number of links. Experiments show thata Giga bit Ethernet port consumes 2 or 3 W with an additionof a link. The same results are reported in [5], thus, we canconclude that the dynamic control for transmission capacitywith traffic volume is one of the important and effective ways
to reduce the power consumption in a network.
Here, we examine a scheme for achieving the dynamiccontrol of the transmission capacity between switches inorder to reduce the power consumption, based upon thechange in traffic volume. In this context, Link Aggregation
is used to dynamically and gradually control the transmission
speed. As for the demo system, Ethernet Bonding (trunking)technology is used to form a single logical link. Two PCs,
which emulate the network switch, dynamically control thenumber of links according with the changing arrival traffic.
This demo is intended to explicitly show the possibility of
power conservation with a network itself by adapting thetransmission capacity to arrival traffic. The investigation of the
proposed scheme regarding both the power saving ability andthe effect on communication quality is examined in [6]. As forhow much the proposed scheme saves the power consumption
in real switches, it is difficult to predict because the power
conservation depends on the traffic characteristics. In addition,
further discussions with vendors are required to accommodate
the proposed scheme with corresponding functions in switches,
which we intend to work in near future.
In Section II of this proposal, we explain how our scheme
can estimate changes in traffic volume and establish thenumber of links using Link Aggregation between switches,
followed by the explanation of our demo system in SectionIII.
II. DYNAMIC L INK C ONTROL S CHEME
Our proposed scheme dynamically controls the transmission
capacity between switches depending on the change in traffic
volume by using Link Aggregation. Link Aggregation, which
is used in many backbone switches to increase the transmission
speed, is standardized in IEEE 802.3ad [7], in which LACP
(Link Aggregation Control Protocol) is defined as a method toform a single logical link between switches by combining themultiple physical links. The switch implementing LACP canautomatically form an aggregated link and follow changes inthe condition of link state, such as link failure and physical

(3)Advertise the numberof physical links

SwitchSwitch

TABLE IT HE EQUIPMENT IN DEMO SYSTEM .

LACPDU
PacketAggregator

Aggregator

PCs
Note PCs
Display
UTP Cables

22
1
10

(1)Traffic
Measurement(4)Re-forms a logical link(2)Estimation

Fig. 1.

Modification of LACP.

Throughput

Control IntervalτττFrequencyTime

using the empirical distribution of peak throughput. Although
we could use the distribution of peak throughput provided witha precise statistical analysis method, such as Extreme Value
Theory, a theoretical foundation for the analyzing rare events,
we use empirical distribution as a first step for realizing ouridea.
Fig. 2 shows the measurement and estimation process inour scheme. First, the arriving throughput is measured ina very short term, e.g. 1 millisecond, and peak throughput
values is recorded in each τ period. At the end of eachcontrol interval, an empirical distribution is made from peakthroughput, and next transmission capacity is determined as
it satisfies a predetermined percentile in the distribution. As
the percentile becomes larger, the margin to accommodate
any unexpected increase in traffic volume grows. Finally, thedetermined value of transmission capacity is mapped to thenumber of links, and the switch forms a new logical link bysending LACP DU to the peer.
III. D EMO S YSTEM

Peak
Throughput
x percentile
Next Link SpeedFig. 2.

Estimation Scheme.

link addition by sending LACP DU (Data Unit) packet to thepeer.
Since LACP does not have a function to form a logicallink based on both measurement and estimation of arrival
traffic, we slightly modify LACP as illustrated in Fig. 1 where
modified processes are described as follows:
1) Switch measures the arrival traffic.
2) Switch estimates the number of links in order to satisfy
the traffic demand.
3) Switch sends LACP DU packet to the peer to notify thenumber of links to form a new logical link.
4) Peer re-forms a logical link with the notified number oflinks.
The important key in our scheme is the estimation of therequired transmission capacity, based on the measurementof arrival traffic. We propose a scheme to determine thetransmission capacity (i.e., the number of links to form alogical link) based on the peak value of throughput. Morespecifically, we estimate the necessary transmission capacity,

Our demo is implemented with two PCs which emulate thenetwork switch. In order to provide multiple links between
PCs corresponding with switch’s ports, each PC has 2 NICs
which have quad ports. As shown in Fig. 3, each PC is directly
connected to the other by eight UTP cables.
As mentioned in Sec. II, our proposed scheme uses LACP
to dynamically control the transmission capacity betweenswitches. In order to achieve the same control in the demo
system, Ethernet Bonding (trunking) technology is used toform a single logical link.
Traffic is generated and communicated by two note PCs, via
the two PCs, which emulate network switch with our proposed
scheme. Two PCs dynamically control the number of links
according with the arrival traffic, which is randomly varied bytraffic generator on note PCs.
Our demo system and GUI are shown in Fig. 4 and Fig. 5.
The left side of Fig. 5 visualizes the active number of links
which is estimated by our proposed scheme based upon thechange in traffic volume. On the right side, presented are thereceived traffic ratio, number of link change, drop packet, anddelay of link. Required space is 180 × 90 cm, in which
the two PCs and two note PCs are deployed. Setup time isapproximately one hour. Our demo system, consisted of twoPCs, two note PCs, and a display, requires approximately
15 ampere of power. Wired internet access is needed for
PC’s maintenance. The equipments used in our demo aresummarized in Table I.

ACKNOWLEDGMENT
This work was supported in part by the Ministry of Education, Culture, Sports, Science and Technology, Grant-in-Aidfor Young Scientists (B)(No. 21700081), and in part by theGreenIT Project by the New Energy and Industrial Technology
Development Organization (NEDO).
R EFERENCES[1] M. Gupta, S. Singh, “Greening of the Internet, ”Proc. of ACM SIGCOMM ’03, pp. 19–26, August 2003.
[2] B. Nordman, “Networks, Energy, and Energy Efficiency,” presentation
at Cisco Green Research Symposium, March 2008.
[3] Cisco Systems,
http : //newsroom.cisco.com/dlls/2009/prod0 60909.html, June
2009[4] S. Gochman, R. Ronen, I. Anati, A. Berkovits, T. Kurts, A. Naveh,
A. Saeed, Z. Sperber, and R. C. Valentine, “The Intel Pentium M Processor: Microarchitecture and Performance,” Intel Technology Journal,
V.7, Issue 2, 2003.
[5] C. Gunaratne, K. Christensen, B. Nordman, “Managing energy consumption costs in desktop PCs and LAN switches with proxying, split TCPconnections, and scaling of link speed,” International Journal of Network
Management Volume 15, Issue 5, pp. 297-310, September 2005.
[6] Y. Fukuda, T. Ikenaga, H. Tamura, M. Uchida, K. Kawahara, andY. Oie, “Performance Evaluation of Power Saving Scheme with DynamicTransmission Capacity Control,” to be appeared in 2nd International
Workshop on Green Communications, December 2009.
[7] IEEE 802.3ad Link Aggregation Task Force,
http : //www.ieee802.org/3/ad/index.html

Fig. 3.

Two PCs are connected by eight cables with each other.

Fig. 4.

Demo System.

Fig. 5.

GUI.