BSc Honours Computer Networking Honours Project 2009/2010 School of Computing Power Consumption of Network Devices Author Matriculation No. Andrew Jess B00113374 Supervisors: Duncan Thomson, Fraser Clark
BSc Honours Computer Networking
Honours Project 2009/2010
School of Computing
Power Consumption of Network Devices
Author Matriculation No.
Andrew Jess B00113374
Supervisors:
Duncan Thomson, Fraser Clark
2 "Power Consumption of Network Devices” Andrew Jess
Form to Accompany Undergraduate Dissertation
To be completed in full:
Surname: Jess
First Name: Andrew Initial: J.
Matriculation No. B00113374
Program Code: COMPNAM
Course Description: BSc Honours Computer Networking
Project Supervisor: Duncan Thomson
Dissertation Title: “Power Consumption of Network Devices”
Session: 2009/2010
Please ensure that a copy of this form is bound with your dissertation before
submission
3 "Power Consumption of Network Devices” Andrew Jess
DECLARATION
This dissertation is submitted in partial fulfilment of the requirements for the Degree of
Bachelor of Science (Honours) in Computer Networking, and accords with the
University Regulations.
I declare that this document embodies the results of my own work and that it has been
composed by me alone. Following normal academic conventions, I have made due
acknowledgement of the work of others.
I understand that passing dissertations will be made available in the library along with
the grades received (for project and dissertation) in order to assist future students.
Signed:
Date:
________________________________________________________________________
To be filled in by project co-ordinator before submission to library and after program
panels
Grade for dissertation:
Grade for project:
4 "Power Consumption of Network Devices” Andrew Jess
ABSTRACT
Power consumption in large Information Technology (IT) installations is an ever
increasing concern for businesses and network professionals. By seeking to reduce the
amount of power consumed by their networks, financial savings can be gained in the
form of reduced electricity overheads.
This project explores several areas pertinent to the power consumption of network
devices. It is observed through experimentation whether the load placed upon devices
(in both a computational and a network traffic sense) impacts the amount of power they
consume. The theoretical power requirements of data communication in general are
also considered by considering a model for Ethernet transmission. Finally, it is
demonstrated just how much power network-enabled devices require in a typical
network (in this case represented by a study of the University of the West of Scotland’s
Paisley campus).
The results of the power study conducted show just how much power is consumed by
medium-to-large computer networks. Areas where power can be conserved are also
apparent through this investigation, showing the potential for huge financial savings.
A combination of a theoretical investigation and experimentation shows that network
switching devices have relatively steady power draws, even when placed under
considerable amounts of traffic. Network-enabled workstations on the other hand were
shown to have more demanding power requirements, showing that the network
professional’s efforts in reducing power consumption of a network are best directed at
maintaining workstations in as low a power mode as possible.
The conclusions of this project are directly applicable to all businesses concerned about
the amount of power consumed by their computer networks: The potential to reduce
electricity overheads in computer networks is present and in many cases is extremely
realisable.
5 "Power Consumption of Network Devices” Andrew Jess
ACKNOWLEDGEMENTS
I would like to extend my thanks to Duncan Thomson and Fraser Clark for keeping me
on the right path throughout this project, and also to Graham Manwell for the insights
and resources he provided.
A debt of gratitude is also owed to Chris Marshall, Julie Sword and Julie Shield of the
University’s IT Services team, without whose valuable assistance much of this project
would have been impossible to complete.
6 "Power Consumption of Network Devices” Andrew Jess
TABLE OF CONTENTS
1. Introduction
1.1 Background .................................................................................................................... 15
1.2 Justification ..................................................................................................................... 16
1.3 Objectives ........................................................................................................................ 16
1.4 Structure .......................................................................................................................... 17
2. Literature Review
2.1 Overview ........................................................................................................................ 18
2.2 Power Management of Devices ................................................................................... 18
2.2.1 Advanced Configuration and Power Interface .................................................. 18
2.2.2 CISCO EnergyWise ................................................................................................ 21
2.3 Present Initiatives .......................................................................................................... 25
2.3.1 EnergyStar ............................................................................................................... 25
2.3.2 Power-over-Ethernet .............................................................................................. 26
2.3.3 Wake-on-LAN ......................................................................................................... 27
2.4 Future Initiatives ............................................................................................................ 29
2.4.1 802.3az ...................................................................................................................... 29
2.4.2 Adaptive Link Rate ................................................................................................ 29
2.4.3 Pause Power Cycle ................................................................................................. 32
2.4.4 Proxying ................................................................................................................... 33
2.5 Chapter Summary ......................................................................................................... 36
7 "Power Consumption of Network Devices” Andrew Jess
3. Power Requirements of ACPI Compliant Devices
3.1 Overview ........................................................................................................................ 37
3.2 Methodology ................................................................................................................... 38
3.3 Procedure ......................................................................................................................... 39
3.3.1 Results for Optiplex GX620 ................................................................................... 39
3.3.2 Discussion ............................................................................................................... 40
3.3.3 Results for HP dc7900 Small Form Factor ........................................................... 41
3.3.4 Discussion ................................................................................................................ 42
3.4 Chapter Summary ......................................................................................................... 43
4. Power Requirements of Network Infrastructure Devices
4.1 Overview ........................................................................................................................ 44
4.2 Methodology ................................................................................................................... 44
4.3 Procedure ........................................................................................................................ 49
4.4 Results ............................................................................................................................. 49
4.5 Chapter Summary ......................................................................................................... 50
5. Theoretical Power Requirements of Data Transmission
5.1 Overview ........................................................................................................................ 51
5.2 Introduction to the PHY ............................................................................................... 53
5.3 Modelling Data Transmission ...................................................................................... 55
5.3.1 Overview ................................................................................................................. 55
5.3.2 Data Encoding Scheme .......................................................................................... 55
5.3.3 The Role of Impedance .......................................................................................... 58
8 "Power Consumption of Network Devices” Andrew Jess
5.4 Forming a Calculation................................................................................................... 59
5.5 Results ............................................................................................................................. 60
5.6 Considerations ............................................................................................................... 61
5.7 Chapter Summary ......................................................................................................... 62
5.7.1 Conclusions ............................................................................................................. 62
5.7.2 Comparison to Obtained Results ........................................................................ 63
6. Power Consumption Analysis for the University of the West of Scotland
6.1 Overview ........................................................................................................................ 64
6.2 Choosing a Methodology ............................................................................................. 65
6.2.1 “Energy Consumption by Office and Telecommunications Equipment in
Commercial Buildings” by Roth et al. (2002) ..................................................................... 66
6.2.1.1 Overview ............................................................................................................. 66
6.2.1.2 Sample Analysis: Network Devices ............................................................... 68
6.2.1.3 Findings .............................................................................................................. 71
6.2.2 "Case study of data centers’ energy performance" by Sun & Lee (2005) ........ 72
6.2.2.1 Overview ............................................................................................................ 72
6.2.2.2 Findings .............................................................................................................. 75
6.3 Conclusions & Chosen Methodology ......................................................................... 76
6.4 Out-of-scope areas ......................................................................................................... 77
6.4.1 Overview ................................................................................................................. 77
6.4.2 From Roth’s Study .................................................................................................. 77
6.4.3 From Sun & Lee’s Study ........................................................................................ 78
6.4.4 From the Paisley Campus Network ..................................................................... 79
9 "Power Consumption of Network Devices” Andrew Jess
6.5 Implementation of Methodology ................................................................................ 80
6.5.1 Summary of Results ............................................................................................... 80
6.5.2 Personal Computers (PCs) .................................................................................... 82
6.5.2.1 Background ........................................................................................................ 82
6.5.2.2 AEC Calculation for PCs .................................................................................. 82
6.5.2.3 Conclusions ........................................................................................................ 87
6.5.3 Monitors ................................................................................................................... 88
6.5.3.1 Background ........................................................................................................ 88
6.5.3.2 AEC Calculations for Monitors ....................................................................... 88
6.5.3.3 Conclusions ........................................................................................................ 92
6.5.4 Printers ..................................................................................................................... 93
6.5.4.1 Background ........................................................................................................ 93
6.5.4.2 AEC Calculations for Printers .......................................................................... 94
6.5.4.3 Conclusions ...................................................................................................... 102
6.5.5 Server Computers ..................................................................................................... 103
6.5.5.1 Background ...................................................................................................... 103
6.5.5.2 AEC Calculation for Servers .......................................................................... 104
6.5.5.3 Conclusions ...................................................................................................... 106
6.5.6 Network Infrastructure Equipment ................................................................... 107
6.5.6.1 Hubs .................................................................................................................. 107
6.5.6.2 Switching & Routing ...................................................................................... 107
6.5.6.3 Conclusions ...................................................................................................... 113
6.6 Comparison to Original Study................................................................................... 114
6.6.1 Overview ............................................................................................................... 114
10 "Power Consumption of Network Devices” Andrew Jess
6.6.2 PCs & Workstations ............................................................................................. 115
6.6.3 Monitors ................................................................................................................. 115
6.6.4 Printers ................................................................................................................... 115
6.6.5 Server Computers ................................................................................................. 116
6.6.6 Network Infrastructure Devices ......................................................................... 116
6.7 Chapter Summary ....................................................................................................... 117
7. Critical Evaluation
7.1 Completion of Objectives ........................................................................................... 118
Objective 1 ............................................................................................................................. 118
Objective 2 ............................................................................................................................. 118
Objective 3 ............................................................................................................................. 118
Objective 4 ............................................................................................................................. 119
Objective 5 ............................................................................................................................. 119
7.2 Areas of Concern ......................................................................................................... 120
7.3 Project Management .................................................................................................... 121
7.4 Future Work ................................................................................................................. 122
7.5 Summary ....................................................................................................................... 123
8. References & Bibliography.......................................................................................124
11 "Power Consumption of Network Devices” Andrew Jess
TABLE OF APPENDICES
Appendix A: Project Brief ...................................................................................................... 128
Appendix B: Optiplex GX620 Datasheet ............................................................................. 130
Appendix C: HP dc7900 Small Form Factor Datasheet ..................................................... 131
Appendix D: CISCO Catalyst 1900 Datasheet .................................................................... 132
Appendix E: Estimated Stock of Student & Staff PCs ........................................................ 133
Appendix F: Estimated Stock of Student & Staff Printers ................................................. 134
Appendix G: Staff Printer Distribution Survey .................................................................. 135
Appendix H: HP LaserJet 9050n Datasheet ......................................................................... 137
Appendix I: HP LaserJet 4250tn Datasheet ......................................................................... 139
Appendix J: HP LaserJet P2055d datasheet ......................................................................... 140
Appendix K: HP Deskjet 880c Datasheet ............................................................................. 141
Appendix L: IBM x3650 Datasheet ....................................................................................... 142
Appendix M: IBM x3850m2 Datasheet ................................................................................ 143
Appendix N: BladeCenter H Chassis Datasheet................................................................. 144
Appendix O: Netgear FS728TP datasheet ........................................................................... 145
Appendix P: Catalyst 6509-E Power Draw Information .................................................... 146
Appendix Q: CISCO ASA 558-40 Datasheet ........................................................................ 147
12 "Power Consumption of Network Devices” Andrew Jess
TABLE OF FIGURES
Figure 2.1: The form of a typical magic packet........................................................ 28
Figure 2.2: PPC in operation....................................................................................... 32
Figure 2.3: The operation of a proxy.......................................................................... 34
Figure 3.1: Setup of Experiment................................................................................. 37
Figure 4.1: Setup of Experiment................................................................................. 44
Figure 4.2: Diagram showing the exchange of ping –fs 65507 packets........ 48
Figure 4.3: The UTL mode of the CISCO 1900 in “Under Load” mode............... 48
Figure 5.1: The subsystems of the 10BASE-T technology....................................... 53
Figure 5.2: Diagrams detailing straight through and crossover wiring
schemes for 10BASE-T. Only pairs actively used in the
transmission/reception of data are portrayed...................................... 54
Figure 5.3: The transmission of data, represented as a circuit.............................. 55
Figure 5.4: Manchester coding symbols................................................................... 56
Figure 5.5: An example of two sample signals in Manchester code,
a preamble (0101010) and a full block of 1’s (1111111)....................... 57
Figure 5.6: A standard power equation.................................................................... 59
Figure 5.7: The same equation, following substitution of characteristic
impedance ................................................................................................ 59
Figure 6.1: Roth’s hub AEC calculation.................................................................... 68
Figure 6.2: Roth’s router AEC calculation................................................................ 70
Figure 6.3: Roth’s WAN Switch AEC calculation .................................................... 70
Figure 6.4: Deployment of Staff PCs across Paisley Campus................................ 82
Figure 6.5: Deployment of Student PCs across Paisley Campus........................... 83
Figure 6.6: Deployment of Student Printers across Paisley Campus................... 94
Figure 6.7: Deployment of Student Printers across Paisley Campus................... 95
13 "Power Consumption of Network Devices” Andrew Jess
TABLE OF TABLES
Table 2.1: S-States of the ACPI Standard ............................................................... 19
Table 2.2: CISCO EnergyWise Category & Power Level Table ......................... 22
Table 3.1: Results for Optiplex GX620..................................................................... 39
Table 3.2: Results for HP dc7900 Small Form Factor............................................. 41
Table 4.1: Bandwidth Utilization Scale with twelve 10BaseT Ports.................... 45
Table 4.2: Results of Experiment.............................................................................. 49
Table 6.1: Sun & Lee’s Device Criteria..................................................................... 73
Table 6.2: Usage times per power mode, per PC (hours/year) ........................... 84
Table 6.3: Power draw of typical PCs in each power mode................................. 85
Table 6.4: AEC Calculation for PCs......................................................................... 86
Table 6.5: Description of Monitor Power Modes................................................... 89
Table 6.6: Power draw of monitor in various modes............................................ 90
Table 6.7: AEC of Monitors....................................................................................... 91
Table 6.8: Power states of printers........................................................................... 99
Table 6.9: Typical and average power draws for printers.................................... 100
Table 6.10: AEC of Printers......................................................................................... 101
Table 6.11: Server Distribution across University.................................................... 104
Table 6.12: AEC of Rack Mounted Servers............................................................... 105
Table 6.13: AEC of Blade Server Installation............................................................ 105
Table 6.14: Power-per-port for Access Layer Switches........................................... 109
Table 6.15: AEC of Access Layer Switches................................................................ 110
Table 6.16: AEC of Catalyst 6509-E............................................................................ 112
Table 6.17: AEC of CISCO ASA 5580-40 devices..................................................... 112
14 "Power Consumption of Network Devices” Andrew Jess
TABLE OF GRAPHS & CHARTS
Graph 3.1: Results for OptiPlex GX620..................................................................... 40
Graph 3.2: Results for HP dc7900 Small Form Factor............................................. 42
Graph 4.1: Results of Experiment.............................................................................. 49
Graph 5.1: Power Consumption of 10BASE-T Ethernet: The results
of the equation performed over all possible impedances................... 60
Chart 6.1: AEC of all Office Equipment (Roth) ......................................................66
Chart 6.2: AEC of Network Infrastructure Devices (Roth) .................................. 68
Chart 6.3: Breakdown of energy use of a data centre (Sun & Lee).................... 74
Chart 6.4: AEC Consumption for the University of the
West of Scotland, Paisley Campus......................................................... 80
Chart 6.5: AEC of Personal Computers................................................................... 86
Chart 6.6: AEC of Monitors....................................................................................... 91
Chart 6.7: Distribution of printer use across staff.................................................. 96
Chart 6.8: AEC of Printers......................................................................................... 101
Chart 6.9: AEC of Server Devices............................................................................. 106
Chart 6.10: AEC of Switching & Routing Devices................................................... 113
Chart 6.11: A comparison of the current study with Roth’s 2002 report.............. 114
15 "Power Consumption of Network Devices” Andrew Jess
1 INTRODUCTION
1.1 B A C K G R O U N D
As the prices of energy continually rise in today’s world, commercial businesses,
manufacturers and home users alike are all under enormous pressure from international
energy efficiency organisations to ensure their computer equipment is environmentally
friendly. “Greening” equipment and operations offers companies numerous advantages
not only in energy bill savings, but also in terms of reducing CO2 emissions and
increasing the company’s environmental reputation (which is of inestimable value).
However, with Information Technology (IT) becoming ever more abundant within
enterprises, and with a mounting need for a strong network backbone to serve and
process these installations’ data, more and more electricity is required to power them.
One of the more notable studies on the power consumption of office and
telecommunications equipment estimated the United States’ annual power consumption
at 97TW-h in 2002 [1], an annual cost of $7.65 million† (£4.62 million). A projection of
energy prices published in 2005 anticipated electricity price increases of 10% between
2005 and 2010 [3]. When this figure is coupled with the staggering adoption rate in the
IT sector (an investment proportion of 40% in 1998, and rising [4]), it can be assured that
energy bills will follow a similar upwards pattern.
† 2002 price of 7.89 cents per kW-h [2]
16 "Power Consumption of Network Devices” Andrew Jess
1.2 J U S T I F I C A T I O N
Although several studies with enormous scope have been performed considering the
“energy footprint” of office equipment and data centre operation, there has been little to
no work on the subject of network-enabled devices specifically. When considering the
rising importance of information and its availability in modern organisations, there is a
considerable demand for the investigation of the power consumption of the devices that
provide this service.
Also of interest is an examination of the literature available outlining the specification of
numerous enhancements to the Ethernet standard. Being proposed at the time of
writing, these technologies will result in the increased energy efficiency of existing data
links. A detailed exploration of several of these breakthroughs, along other notable
developments, will be contained within this report’s literature review.
1.3 O B J E C T I V E S
Five objectives will be met by this project:
1. Investigate the costs involved in maintaining the operation of a typical
organisation’s IT infrastructure.
2. Investigate and calculate the theoretical power requirements of data
transmission.
3. Observe and measure the power consumption of devices in a typical
network, both under load and whilst idle.
4. Compare and analyse observed power usage data against theoretical
projections. (Advanced)
5. Compare the power usage of idle devices with those under load. (Advanced)
These objectives are shown in the Project Brief document, included as Appendix A.
17 "Power Consumption of Network Devices” Andrew Jess
1.4 S T R U C T U R E
The project has been organised into the following chapters:
Chapter 2 outlines a study of literature exploring the areas of existing power
management standards for network devices and a set of schemes already in place that
seek to improve the power efficiency of devices. Also explored are future technologies
that propose energy saving improvements to Ethernet data transmission schemes.
Chapter 3 presents the results of an experiment performed on typical network-enabled
computer hardware examining the link between system power state and overall power
consumption.
Chapter 4 expands this experiment to consider other network devices, performing a load-
based examination of power consumption on a typical network switch. The aim of this
chapter is to explore the effect of network traffic on power consumption while also
providing contextual results to be verified in the following chapter.
Chapter 5 attempts to investigate the theoretical power requirements of data
transmissions. The chapter’s aim is to produce calculations detailing the power
requirements of 10BASE-T Ethernet data transmission. From here, a comparison of
theoretical and measured power consumption can be made and with a view to verifying
the results of the experiment.
Chapter 6 details a “case study” of power consumption for the University of the West of
Scotland’s Paisley campus. First, existing power study methodologies are examined and
the most suitable chosen. From here, the chosen methodology is applied to the campus
and results presented along with any appropriate conclusions or recommendations.
Chapter 7 evaluates how well the specified objectives have been completed. Areas of
further study are identified which may prove worthwhile to future students. The
performance of the project from a management perspective is also considered.
18 "Power Consumption of Network Devices” Andrew Jess
2 LITERATURE REVIEW
2.1 O V E R V I E W
This chapter explores a selection of literature relating to the power consumption of
network devices, first exploring existing standards that determine the power state of
common device types. Also present is an examination of present and future initiatives
relating to the power efficiency of devices and Ethernet data transmission.
2.2 P O W E R M A N A G E M E N T O F DE V I C E S
2 . 2 . 1 A d v a n c e d C o n f i g u r a t i o n a n d P o w e r I n t e r f a c e
Network devices, regardless of their type can all be considered to have certain modes of
operation. Although certain types of IT equipment can only be considered “on” or “off”,
more advanced devices such as workstations and network infrastructure devices can be
powered down to intermediate levels where less power is consumed. Any one type of
device can have different rates of energy consumption depending on the mode it is
being run in.
The Advanced Configuration and Power Interface (ACPI) standard defines a set of
power states for systems and devices and was developed in conjunction with major
software vendors including Hewlett-Packard, Intel and Microsoft. Support also exists
for migrating Linux machines to this standard [5]. Table 2.1 describes a list of system “S-
States” which define the power status of an ACPI-compliant workstation.
19 "Power Consumption of Network Devices” Andrew Jess
ACPI Level Mode Name Function
S0 Working
The system is operating normally, all components are receiving
power.
Although not mentioned in the ACPI standard, Roth et al. note the
distinction between active-idle (where the system is not actively
processing) and active-processing (where the system is performing
computations [6]) and as such there can be a wide difference in
power requirements from devices in this mode.
S1 to S4 Sleep
Levels S1 to S4 all define sleep levels of variable depth. S1 preserves
most operation and conserves the least amount of power, whereas S4
provides the largest savings and powers down every possible
component of the system.
Microsoft Windows computers commonly use Standby as their
primary power saving mode. This mode operates at level S3. Here,
user data is stored in RAM and non-essential components of the
system are shut down. The CPU is provided no power, hard disks
are switched off but RAM is in a constant “refresh mode” to keep the
user’s data intact.
S4 mode is supported by more recent operating systems and is
known as “hibernate”. This mode saves more power than its
standby equivalent by saving an image of the system’s memory to
hard disk before powering down, eliminating the need for the
system’s RAM to be refreshed.
S5 Soft Off
System is completely powered down and requires a full reboot to
return to S0 state. The system is still connected to the mains supply
and draws a nominal amount of power (as mentioned below).
“S6” (G3) Mechanical
Off
Not a part of the official ACPI standard, state S6 is sometimes used
to refer to the global “mechanical off” state G3 [7] and implies that
the supply of electricity is physically removed from the system.
Table 2.1: S-States of the ACPI Standard [8]
It should be observed that even if a computer is considered to be in S5 mode, it will still
draw a nominal amount of power. Roth’s measurements show that even when powered
off (but still plugged in) personal computers and notebooks still draw 2W [6].
20 "Power Consumption of Network Devices” Andrew Jess
This phenomenon is known as “phantom load” and is common to all electronic devices.
Also known as “standby power” or “vampire power”, it has been identified as a major
source of energy wastage and has been a focus of many governments’ energy efficiency
undertakings [9].
As such, discussions considering the benefits and drawbacks of standby modes are
frequent. With the difference of power consumption between S3 and S5 modes being so
small, leaving a system in standby mode overnight may be almost as energy efficient as
shutting it down. Harris & Cahill go as far to suggest that power mode transitions from
deeper ACPI modes typically consume extra energy (due to device start-ups) and can
even reduce a system’s mechanical lifetime (due to physical wear)[10]. However,
despite these discussions, it cannot be argued that putting a device into “S6 mode”
garners more savings than both S3 and S5 modes. Removing a device from the
electricity supply always reduces its power requirements to zero.
The ACPI model pertains mainly to personal computing systems developed by the
contributing vendors. For other network infrastructure devices, the CISCO EnergyWise
initiative uses a scale similar to (but greater in scope than) the ACPI model which all
network devices would comply to.
21 "Power Consumption of Network Devices” Andrew Jess
2 . 2 . 2 C I S C O E n e r g y W i s e
IT devices and their infrastructure are not the only consumers of electricity in an
organisation. As lighting and heating alone account for 66% of an organisation’s
electrical energy consumption (compared with IT equipment’s 25-30%) [11], the prospect
of managing complete organisational power consumption underneath one central
system is an appealing idea.
The EnergyWise initiative (developed by CISCO Systems) is a proposed energy
management architecture which seeks to measure and collect power information from
all its connected devices, with an aim to allow administrators to better optimize the
power consumption of an organisation. It goes beyond simply conserving the power of
network-enabled IT equipment and instead aspires to control all aspects of an
organisation’s power usage.
In order to do this, EnergyWise defines several attributes that are used to model the
organisation’s system.
Attribute 1: Categories & Power Levels
Similarly to the ACPI protocol discussed earlier in this review, a common language used
to define power states between devices is required to standardise their management.
ACPI, having applications only for PC workstations and compliant mobile devices
would be an inappropriate choice for EnergyWise. Instead, CISCO developed a new set
of power levels for their management system to utilise, creating a “common lexicon” [11]
between devices so that power levels can be understood. In particular, this meant that
existing power management standards (such as ACPI) could be mapped directly onto
the EnergyWise system.
22 "Power Consumption of Network Devices” Andrew Jess
Table 2.2: CISCO EnergyWise Category & Power Level Table [11]
It should be noted that Table 2.2 has varying levels of complexity depending on the
device it is referring to. For example simple devices such as lighting grids may only use
two modes, Operational and Non-Operational. More complex devices such as PCs will
have their ACPI modes married up with a “level” in the table above.
Attribute 2: Entities
Entities represent power consuming devices connected to the EnergyWise network and
can consist of several different types. Entities may be IP-based (even differentiating
between Power-over-Ethernet IP and standard Ethernet IP) or not. A category exists as
well for devices that operate systems unrelated to the IT infrastructure of the network,
such as heating or lighting systems. Devices, no matter what type, are considered
children of the EnergyWise enabled controller that they are connected to. Network
switches typically act as these controllers, representing the entities that management
systems will interface with in order to control the EnergyWise system.
23 "Power Consumption of Network Devices” Andrew Jess
Attribute 3: Domains
Each entity as described above must be a member of a domain. This allows devices to
be logically arranged into groups to allow more effective management of the network (in
turn better facilitating its expansion). For example, sets of switches (and their children)
could be grouped together based on the building floor they reside on.
Attribute 4: Management Communications
EnergyWise also defines its own communication methods in order to send commands
from a central management location to its devices. CISCO has suggested two methods
to implement this. The first is to send messages using the Simple Network Management
Protocol (SNMP) which provides a framework for network administration tasks.
EnergyWise provides its own Management Information Bases (MIBs) defining how to
handle data produced by the system. This allows for simple management of one switch;
however Lippis notes that the limitations of SNMP make it unsuitable for managing
domains containing more than one switch [11].
Alternatively, a single “Management Port” can be defined on a central controller switch
that will allow administrators to gather domain-wide information by issuing commands
to it. Support for requesting and changing the power levels for tens of thousands of
entities is purportedly possible [11].
24 "Power Consumption of Network Devices” Andrew Jess
Attribute 5: Management Applications & API
In order to control the EnergyWise network, CISCO have provided a common API in
order to allow third-party vendors to develop network management applications
utilising EnergyWise information. The API allows power consumption and device
efficiency data to be pulled simply from the network and be translated into meaningful
colour-coded topologies. This would allow companies which have already published
software controlling various aspects of a network to easily allow power-state
management to the set of features offered.
The advent of EnergyWise promises to expand the role of switches within a network.
Instead of switching only traditional IP traffic, switches will soon become responsible for
delivering management instructions to devices or gathering reports of power
consumption over a period of time. As non-IT devices are incorporated into the
EnergyWise topology, switches may soon be able to perform such complex functions as
alter the temperature of a building depending on the time of day. The scope for
financial savings that can be gathered by a system such as this is huge, with switches
being able to orchestrate the power states of devices automatically on a regular basis.
25 "Power Consumption of Network Devices” Andrew Jess
2.3 P R E S E N T I N I T I A T I V E S
A number of initiatives have been undertaken in order to kerb the amount of energy
used by IT infrastructure, network devices and more widely, electrical devices as a
whole:
2 . 3 . 1 E n e r g y S t a r
EnergyStar is a standard specifying power consumption requirements for a range of
electronic devices. Originally created in 1992 as an American government-funded
program to encourage computer manufacturers to include power management options
in their products [12], it has since expanded to consider consumer and commercial
products, as well as devices such as lighting and air conditioners [13]. As a voluntary
accreditation, it is not required for manufacturers to subscribe to, but its high reputation
amongst consumer groups provides incentive for compliance.
EnergyStar’s current fifth specification revision maintains directives on a number of
different computer systems. Desktop computers, notebooks, games consoles and
workstations amongst others are all included. However, server computers and more
recent mobile devices (PDAs and smart phones) are not included in the specification
[14]. Also of note is their specification for notebook computers which requires a low-
power mode consuming no more than 15W, which McWhinney notes that a large
percentage of notebooks comply with [15].
EnergyStar has proven to be a very popular scheme, as demonstrated by its international
expansion and the range of devices it now covers. In their 2006 annual report,
EnergyStar reported that compliant desktop computers are shown to save between 5%
and 55% more power than their non-accredited counterparts. The program in its
entirety also published annual savings of $13.7 million in the year of publication, along
with considerable emission reductions from the year of 2000 onwards [13]. As such,
companies with large IT outlays can be assured that purchasing products accredited by
EnergyStar conserves more energy and creates less carbon emissions.
26 "Power Consumption of Network Devices” Andrew Jess
2 . 3 . 2 P o w e r - o v e r - E t h e r n e t
Power-over-Ethernet (PoE) describes a set of standards which define a method of
transmitting power over an Ethernet link whilst not disturbing the data contained on it.
First published as 802.3af in 2003, a new version of the standard known as 802.3at was
recently approved in September 2009 [16] featuring marked improvements to the
amount of power supported devices could provide. The publication of 802.3af/at also
serves to encourage standardisation of all previous work performed in the same area,
such as CISCO Systems’ “inline power” technology [17].
Originally developed to provide both power and network connectivity to locations
where power cabling was impractical or impossible to provide, the main advantage of
PoE lies in the ability to discard the traditional AC transformer based method of
supplying power to devices. PoE is of particular application to devices such as CCTV
cameras and wireless repeaters (which are often positioned in out of reach locations) as
well as making Voice-over-IP (VoIP) phones resemble their “plain old telephone
system” counterparts more by similarly drawing power from their copper transmission
line).
Two types of devices exist in the operation of PoE:
Power Sourcing Equipment (PSE): PSE equipment is typically a PoE enabled network
switch which supplies electricity to connected devices. Devices known as Midspan
Power Sources (MPS) are also used along with traditional Ethernet switches to “inject”
power into existing Ethernet networks in the absence of a PSE switch.
Powered Device (PD): Connected devices are known as PDs, and are supplied power
from the PSE via twisted pair cable. The 802.3af specification provides only around 13W
of power to be supplied [18]. Whilst certainly not enough to power larger devices such
as PCs and large printers, PoE has found a niche powering smaller pieces of equipment
that only require nominal amounts of energy.
27 "Power Consumption of Network Devices” Andrew Jess
Despite the clear advantages that a PoE infrastructure would bring to an organisation,
attention must be paid to the backwards compatibility of the platform. As thousands of
varieties of standard Ethernet equipment have been deployed across the world without
the ability to accept power [18], it would be foolish to arbitrarily inject power into them
and risk damage or device failures. To prevent this, a discovery process is embedded
into DSE devices which maintain their ports in a low-power state until devices are
determined to be PoE compliant. A tentative low voltage (in the range of 2.7V to 10.1V)
is then applied to a PD upon connection and the PSE checks for a built in a “signature
resistance” of 25kΩ before supplying larger amounts of power [19].
Additional concerns have been raised [18] over the safety of using existing 8P8C
connectors† to supply power with, particularly as the female socket is large enough for a
small finger to be inserted into. However, as the 802.3af standard only provides a small
DC voltage (48V) and an extremely low current (up to 300-375mA maximum) [18, 19]
through the twisted pair wire, no harm can be caused.
2 . 3 . 3 W a k e - o n - L A N
Wake-on-LAN (WoL) is a technology designed to be used with Ethernet-compliant
devices and permits them to be turned on via network communication from another
device. WoL has been available for over a decade with various implementations
supported by different hardware vendors [20, 21].
Prior to the introduction of WoL, computers could only be communicated with if they
were in an ACPI S0 state. When technicians realised that they required a method to
communicate with computers kept in other states, WoL was developed in order to
“pull” a device out of its low power state and back into S0 mode.
† also erroneously referred to as “RJ-45”connectors
28 "Power Consumption of Network Devices” Andrew Jess
WoL functions by requiring a device’s network adapter to remain operational whilst the
rest of the device is powered down. This results in a nominal amount of “standby-
power” being drawn by the device to keep it operational. The network adapter of the
device would also contain software that continually listened for “magic packets”. Upon
the reception of a magic packet, the network adapter would send a signal to its host,
prompting it to “wake up” into S0 mode.
A “magic packet” requires a certain sequence to be contained within it in order to
awaken a system. It can appear anywhere in the packet’s payload, but the sequence
must take the form of six “one” bytes (each represented by FF) followed by sixteen full
iterations of the device’s six byte MAC address (represented in Figure 2.1 as 11 22 33 44
55 66).
Figure 2.1: The form of a typical magic packet [20]
WoL could find a valuable place as part of an organisation’s power management plan.
It would be possible for administrators to remotely power on machines on an as-needed
basis rather than remain powered on indefinitely. However, one of WoL’s limitations is
its unidirectional nature, only being able to wake systems. A worthwhile expansion of
the technology would allow magic packets to shut down systems remotely. “Proxying”
(discussed later in this chapter) can be considered in some regards as a more
sophisticated implementation of WoL.
29 "Power Consumption of Network Devices” Andrew Jess
2.4 F U T U R E IN I T I A T I V E S
2 . 4 . 1 8 0 2 . 3 a z
In October 2007, the Institute of Electrical and Electronics Engineers (IEEE) approved the
802.3az project to investigate and improve the energy efficiency of the 802.3 Ethernet
standards. Its main objectives involve developing techniques for lowering the power
use of Ethernet whilst retaining compatibility with the current physical media that use it.
As Ethernet is a family of technologies operating at OSI Layer 1 and 2 and is used in the
majority of Local Area Networks (LANs) today, incorporating energy saving techniques
into the technologies themselves will yield savings from every network that utilises
them.
Currently the 802.3az project has published proposals highlighting three techniques
which could increase the energy efficiency of Ethernet devices. Although distinct in
their application, each proposal brings attention to the fact that most networks are kept
on 24 hours a day, even when they aren’t required by users.
2 . 4 . 2 A d a p t i v e L i n k R a t e
The first proposal published by the 802.3az project was a paper on using Adaptive Link
Rate (ALR) mechanisms as a method of controlling the power usage of Ethernet links
[22]. ALR was developed and refined out of the realisation that Ethernet links remain
idle or in low use for a very large proportion of the time (with studies showing average
Ethernet link utilisation of only 1% [23]).
30 "Power Consumption of Network Devices” Andrew Jess
Bennett proposes in his proposal that as the capacity of network media and transmitters
increase so will the energy required to power and maintain the links. They observe that
Ethernet links operating at 1Gbps require 2W more power at each transmitter than
equivalent links operating at 100Mbps. As such they propose that during periods of low
network usage, ALR would allow Ethernet links to “step down” transmission speeds in
order to save power. Similarly, links would “step up” to higher rates as their services
were demanded.
ALR operates from both ends of the transmission link. Both transmitter and recipient
interfaces would use in-built “policies” to automatically negotiate whether data rates
should be stepped up or down. Working as a handshake mechanism, a change would
be made only if both parties agreed. Factors such as buffer queue thresholds and actual
rate utilisation would considered in this decision. Two scenarios would be possible:
Increase from low data rate to high: The size of the transmitter’s buffer queue is used
in determining the need for a higher data rate. When over a certain amount, the
burdened interface would send a frame to the recipient requesting a transition. If a
higher rate is available, the request to “step-up” must never be denied by the recipient in
order to guarantee maximum throughput.
Decrease from high data rate to low: The link utilisation of the interface would be
monitored. If below a certain threshold, the interface would send a frame requesting a
rate “step-down”. However, if the other interface’s link utilisation did not also fall
beneath the threshold, the request must be denied.
Using conditions such as the above would guarantee that higher data rates would
always take precedence over energy conservation. Also, as “step-up” and “step-down”
requests would be implemented using a fast signalling method at the MAC level,
transitions could take place promptly. This would make the amount of perceived delay
negligible to the user.
31 "Power Consumption of Network Devices” Andrew Jess
As the policies for stepping up and stepping down data rates must be contained in both
transmitter and receiver Ethernet controllers, both devices would have to be compliant
with the ALR protocol. Unfortunately, devices in use today are not. No standard
currently exists for ALR and a considerable amount of work on the “open challenges”
present in the technology must be performed before one will be developed.
Additionally, once a standard has been published, it must be considered whether
existing Ethernet devices be able to comply with it or whether they will have to be
upgraded to more recent devices. If the latter scenario is true, it will almost certainly
cost a considerable amount of money for most businesses to replace every Ethernet
controller present in their network. Even if it becomes possible to upgrade existing
controllers, it will take a considerable amount of time until the technology is widespread
enough to be enforced sufficiently to yield the massive monetary savings heralded by its
authors.
However, a paper by Nedevschi et al. notes that EnergyStar standard proposals for 2009
discuss requirements for Ethernet links to use slower data rates in order to conserve
energy when idle [24]. As such, ALR or a technique similar to it may see inclusion
within the EnergyStar specification in the near future.
32 "Power Consumption of Network Devices” Andrew Jess
2 . 4 . 3 P a u s e P o w e r C y c l e
Pause Power Cycle (PPC) is a method used by LAN switches that involves adapting the
power states of its own components in accordance with the states of the active links that
are connected to them. The author of the technique, Francisco Blanquicet, suggests that
rather than remaining powered on 24 hours a day, the main goal of switches should be
to transmit data as fast as possible and then return to a “low power idle-mode” [25]. The
PPC method is an implementation of this ideology.
Figure 2.2: PPC in operation [25]
Figure 2.2 shows how PPC might be used in a typical network. The switch periodically
sends PAUSE frames to network devices and temporarily powers off the link,
conserving energy. After a timer elapses, the link is then powered back on and resumes
transmission of data.
Blanquicet’s initial calculations on power saving show that the energy conserved by PPC
is directly related to the proportion of time it is powered down. He refers to the ratio of
uptime to downtime as the switch’s “duty cycle” and cites that if it were set at a value of
50% (essentially halving its uptime), the amount of energy required by the device would
be halved.
33 "Power Consumption of Network Devices” Andrew Jess
The amount of energy saved through PPC seems to depend on sacrificing network
throughput. By lowering the amount of time a link is powered on, the effective
transmission speed of the medium is reduced. Banquicet asserts that his technique may
result in occasional buffer overflows in clients (resulting in packet loss) and his
experiments with PPC’s duty cycle set to 50% show the introduction of erroneous
artefacts to streamed video [25]. In high speed environments, such as LANs, this may
not be such an issue, as data can be retransmitted quickly over media with large
capacities. However, in wide area network environments where the available
bandwidth is considerably lower, these errors suggest that PPC may need its duty cycle
set to a less aggressive setting (or be disabled altogether) to provide acceptable
throughput. In conclusion, this technique is a direct trade-off between link quality and
device power consumption.
2 . 4 . 4 P r o x y i n g
September 2007 saw a proposal detailing a process known as “proxying”. The concept
provides a method for network terminals to be able to retain their network connectivity
regardless of their power mode. An additional device (known as the “proxy”) would act
as an intermediary to the terminal and preserve the network presence of its parent
device.
Nordman argues that many messages destined for a workstation don’t require the use of
many of its many “power hungry” components (such as CPU, hard drive and memory)
and can be handled by the network interface card (NIC) itself [26]. The proxy’s main
task would be to identify these messages, generate routine replies for them and
determine whether the device requires to waking up. This would allow a workstation to
remain in a standby power mode while the proxy dealt with maintaining its network
presence.
34 "Power Consumption of Network Devices” Andrew Jess
Figure 2.3: The operation of a proxy [26]
Figure 2.3 demonstrates the process as currently proposed along with the five steps
required for its operation. Three distinct entities are present: the proxy, the sleeping
device and the external network.
1. A scenario arises where the device is in the process of going into sleep mode
(e.g. under user direction, after a period of inactivity)
2. Before completely powering down, the device passes network state and
notice of sleep to the proxy device.
3. On behalf of the device, the proxy maintains full network presence.
4. If the proxy receives a packet that requires device wakeup, it signals to the
device to awaken.
5. Once the device has woken up, the proxy passes the network state back to it
and normal network operation is resumed.
35 "Power Consumption of Network Devices” Andrew Jess
Several different types of proxying are suggested in Nordman’s document:
Self-Proxying: Where the proxy exists as part of one of the device’s components
(typically its NIC) and is controlled under the same operating system. Power
would remain supplied to the proxy component whilst all of the workstation’s
other components would remain off.
Switch-Proxying: Where the proxy exists as part of a network switch’s port that
the device is connected to. Nordman suggests that the mobility of connected
devices may pose an issue to how proxying would be implemented [26].
Existing “Wake-On-LAN” requests may be utilised in its operation.
Third Party Proxying: Where the proxy exists in a third party device such as
another workstation on the network or even a dedicated device.
Proxying still appears to be in its conceptual form as an addition to the Ethernet
standard. Although planned to be become a requirement of EnergyStar compliant
devices [27], many of the proxying processes’ procedures have yet to be defined. In
particular, its authors acknowledge that problems may arise in the implementation of
switch proxying and consider third party proxying as outside the scope of their paper
due to its complexity. They also concede that the fifth stage of the process still lacks the
definitions for the proxy’s role after the host device has woken up.
Proxying as a concept is certainly a fascinating idea, as the infrastructure of computer
networks currently have no conception of the power states of devices connected to it.
The ability to place entire racks of servers into sleep mode until required would
considerably reduce the amount of electricity consumed in data centres, for example.
However, despite its potential to be furnished in future Ethernet hosts, its lack of
maturity (and lack of a published standard) make it an unrealisable method to save
power in computer networks in the near future.
36 "Power Consumption of Network Devices” Andrew Jess
2 .5 C H A P T E R S U M M A R Y
Along with examining how typical host workstations represent their power states, an
exploration of CISCO’s EnergyWise technology shows exactly how the future of
network power management may look. As well as this, initiatives and technologies
seeking to make IT equipment more efficient have been present for several years.
EnergyStar has been a very successful initiative encouraging manufacturers to develop
more energy efficient equipment. Wake-on-LAN technologies have also been used by
network professionals for years to reduce the constant power draw of infrequently used
PCs.
However, much of the future development present in network power conservation
focuses on making Ethernet links themselves more efficient, fore-fronted by the IEEE
802.3az group. Despite a selection of papers exploring a range of interesting
technologies, its recent inception means that standards do not yet exist for them. As
such, it will likely be several years before their draft proposals are accepted by the IEEE
for introduction in Ethernet devices.
37 "Power Consumption of Network Devices” Andrew Jess
3 POWER REQUIREMENTS OF
ACPI COMPLIANT DEVICES
3.1 O V E R V I E W
Several studies [1, 12] have noted that computer systems do not draw a steady level of
power over time; instead their requirements have been shown to fluctuate depending on
the power mode of the system. Industry knowledge of this is reflected in the publishing
of datasheets: they often contain several different power consumption figures for
devices, each reflecting the level of load being put on the device.
This experiment aims to confirm that the power draw of a typical host computer does
change depending on its ACPI mode, satisfying objectives 3 and 5 from one of two
perspectives (the latter being explored in Chapter 4). By measuring the power drawn by
a device over time, the aim is to show each mode draws progressively less power as they
are powered down further. Two models of Personal Computer (PC) will be compared
to show this: A machine of modest specifications, and a higher-powered workstation
PC typically used for 3D rendering and video editing.
Figure 3.1: Setup of Experiment
38 "Power Consumption of Network Devices” Andrew Jess
3.2 M E T H O D O L O G Y
The components and software of each machine remained constant throughout the
experiment with the only altered variable being its ACPI mode. The operating system of
each machine was Microsoft Windows XP Professional. Datasheets for both the
Optiplex GX620 and HP dc7900 Small Form Factor (included as Appendices B and C)
rated the maximum output of their power supply units as 275W and 240W, respectively.
Used to measure the power draw of the system was a Maplin “Plug-In Mains Power &
Energy Monitor” (hereafter referred to as the “power monitor”). It features a power
measurement mode which updates every second with readings to the nearest Watt.
The following ACPI levels were used in the experiment:
S0 (active-processing): Achieved by ensuring high strain activities were being
carried out by the PC. The Direct3D testing portion of Microsoft’s dxdiag tool
was used to ensure that the CPU, GPU and memory of the PC were all being
utilised to a high degree (a load of 90-100%).
S0 (active-idle): Achieved by ensuring that the system had fully booted up and
was performing nothing more than regular housekeeping tasks. Ideally a CPU
load of 0-5% would be used to gather measurements from.
S3 (standby): Achieved by using the “sleep” function available within the
operating system.
S5 (soft-off): Achieved by using the “shutdown” function available within the
operating system.
The systems used had no facility to be placed into the S4 (hibernate) state, and the
“S6”/G3 (mechanical off) state has been omitted due to the fact its results would always
equal 0W.
39 "Power Consumption of Network Devices” Andrew Jess
3.3 P R O C E D U R E
The power monitor was positioned between the plug of the computer system and mains
power supply and set to the power monitoring mode. The system was placed into the
appropriate ACPI mode and the power readings were allowed to stabilise to ensure that
transitions between ACPI modes were not still underway.
Measurements were taken from the power monitor at intervals of 5 seconds for a total of
90 seconds.
3 . 3 . 1 R e s u l t s f o r O p t i p l e x G X 6 2 0
Power
Mode t 0 5 10 15 20 25 30 35 40 45
S0 (active-
processing) 140W 141W 136W 141W 140W 140W 132W 136W 137W 141W
S0 (active-
idle) 79W 79W 79W 79W 79W 80W 80W 79W 79W 79W
S3 (standby) 2W 2W 2W 2W 2W 2W 2W 2W 2W 2W
S5 (soft-off) 2W 2W 2W 2W 2W 2W 2W 2W 2W 2W
Power
Mode t 50 55 60 65 70 75 80 85 90 AVG
S0 (active-
processing) 136W 136W 132W 137W 139W 139W 139W 135W 140W 137.73684W
S0 (active-
idle) 80W 85W 79W 79W 78W 79W 78W 79W 79W 79.36842W
S3 (standby) 2W 2W 2W 2W 2W 2W 2W 2W 2W 2W
S5 (soft-off) 2W 2W 2W 2W 2W 2W 2W 2W 2W 2W
Table 3.1: Results for Optiplex GX620
40 "Power Consumption of Network Devices” Andrew Jess
Graph 3.1: Results for Optiplex GX620
3 . 3 . 2 D i s c u s s i o n
The results of the experiment confirm what was presumed about the power
requirements of ACPI levels, conclusively showing that machines in more functional
states require more power. Powering the system down into S5 and S3 modes expectedly
resulted in lower power consumption than leaving a machine in its S0 (Active-Idle)
state.
It was also shown that the amount of power a system requires depends on how active it
is: Those with more of their components actively processing can draw almost twice as
much power than when idle.
The experiment also proved the presence of the “phantom load” phenomena. In S5
mode, a small amount of power (2W) was still drawn from the supply despite the fact
that the device’s power button had been pressed and was presumed to be off.
41 "Power Consumption of Network Devices” Andrew Jess
Perhaps most surprisingly, the results of this experiment showed that there was no
difference between S3 and S5 states. This suggests that the S3 sleep mode provided with
modern operating systems is indeed a viable alternative to placing the machine in S5
state.
3 . 3 . 3 R e s u l t s f o r H P d c 7 9 0 0 S m a l l F o r m F a c t o r
Power
Mode t 0 5 10 15 20 25 30 35 40 45
S0 (active-
processing) 56W 55W 54W 54W 54W 56W 53W 52W 54W 54W
S0 (active-idle) 31W 32W 31W 31W 30W 31W 31W 33W 31W 31W
S3 (standby) 2W 2W 2W 2W 2W 2W 2W 2W 2W 2W
S5 (soft-off) 2W 2W 2W 2W 2W 2W 2W 2W 2W 2W
Power
Mode t 50 55 60 65 70 75 80 85 90 AVG
S0 (active-
processing) 57W 54W 54W 54W 54W 55W 55W 54W 53W 54.315790W
S0 (active-idle) 30W 31W 31W 33W 31W 31W 30W 31W 31W 31.10526W
S3 (standby) 2W 2W 2W 2W 2W 2W 2W 2W 2W 2W
S5 (soft-off) 2W 2W 2W 2W 2W 2W 2W 2W 2W 2W
Table 3.2: Results for HP dc7900 Small Form Factor
42 "Power Consumption of Network Devices” Andrew Jess
Graph 3.2: Results for HP dc7900 Small Form Factor
3 . 3 . 4 D i s c u s s i o n
The results from a lower specification PC confirm the conclusions reached above. Power
requirement increases are, however, of a lower proportion than the higher specification
machine due to less power being consumed overall.
Phantom load is again confirmed with the S5 reading remaining at the same amount as
before (2W). This suggests that phantom load is either constant, being unrelated to the
capabilities of the system, or that it is more related to the nameplate value of the
system’s PSU (both of which are very similar between these systems).
Again, there was no measured difference between S3 (sleep) and S5 (soft-off) modes,
confirming that S3 can be used as a viable alternative to turning machines off.
43 "Power Consumption of Network Devices” Andrew Jess
3.4 C H A P T E R S U M M A R Y
Between the two machines examined, it was clear that machines developed for different
applications have dissimilar power requirements. Unsurprisingly, machines geared
towards heavy computational tasks (such as rendering 3D models and editing video
files) required more power when placed under strain. The reason for this is most likely
due to their more powerful (and power-hungry) processors and graphics chipsets.
Nameplate values on the power supply seemed to have no relevance to the amount of
power that a machine actually used, even when placed under heavy load. As such,
nameplate values should not be used in power consumption calculations in an
organisation, as the power consumption would be grossly overestimated. Instead,
readings from a meter should be used.
The results also show that S3 and S5 ACPI levels offer large power saving opportunities
for network devices. Enterprises stand to conserve considerable amounts of energy by
placing devices into S3 or S5 whenever their use isn’t required (anywhere thirty to
seventy times, depending on the machine). S3 mode would be recommended for this, as
it allows faster resumption of service with no increased power overhead. For large
organisations, these transitions needn’t be performed manually: technologies which
could place devices into these states remotely (such as CISCO EnergyWise) could aid IT
Staff in automating these transitions, helping to provide maximum savings.
44 "Power Consumption of Network Devices” Andrew Jess
4 POWER REQUIREMENTS OF
NETWORK INFRASTRUCTURE DEVICES
4.1 O V E R V I E W
In order to allow communications between large numbers of IT devices, the use of
numerous hubs, switches and routers are required. However as noted by Coffman &
Odlyzko [23], Ethernet links find themselves sitting idle most of the time. The purpose
of this experiment is to determine how much power these idle links use in comparison
to those which are under constant stress, fulfilling Objectives 3 and 5 from an alternative
perspective.
4 .2 M E T H O D O L O G Y
Figure 4.1: Setup of Experiment
45 "Power Consumption of Network Devices” Andrew Jess
Twelve Optiplex 755 computer systems (running a virtualised Linux operating system)
were connected to the twelve 10BASE-T ports on a CISCO Catalyst 1900 LAN switch
with CAT5 cable. This particular model can be considered typical of a low-end access
layer switch, often widely deployed to enable connectivity to hosts devices on a
network. The default configuration of the switch was used, and connectivity between
the hosts was confirmed using the “ping” command. A data sheet for the switch is
included as Appendix D.
All connected devices were considered peers with no distinction between “server” and
“host”. This configuration was chosen to mimic the operation of the access switching
layer of a typical network.
The variable factor in the experiment would be the “utilisation” of the router. The
CISCO Catalyst 1900 switch contained a control on its front face that allowed access to a
UTL mode that displayed how much of the switch’s bandwidth was being consumed on
the light emitting diodes (LEDs) above its ports. Table 4.1 shows how the switch
represents load on its LEDs.
Table 4.1 Bandwidth Utilization Scale with twelve 10BaseT Ports (adapted from [32])
46 "Power Consumption of Network Devices” Andrew Jess
Three different power states were defined:
Idle-Disconnect: All CAT5 cabling was disconnected from the switch in order to gain a
baseline power consumption reading for the switch. In this mode, the connected devices
had no connectivity to the switch or each other.
Idle: The twelve hosts were connected to the switch while performing no user-initiated
communications tasks with either the switch or each other. Operating system
“housekeeping” tasks, such as the detection of an active connection, would be
performed but their low overhead meant that any load put on the network could be
considered negligible. The UTL mode of the switch should display a maximum of one
illuminated LED.
Under Load: Each of the devices connected to the switch were instructed to send large
amounts of data as fast as possible another device on the network using the following
command:
ping <ip-address> -fs 65507
<ip-address> denotes the IP address of the destination host.
-s 65507 denotes that packets should be the maximum ICMP packet size of 65507
bytes, plus 8 bytes of ICMP header data (resulting in a total packet of 65515 bytes).
-f denotes “flood ping” where ICMP ECHO_REQUEST packets are sent as fast as
responses are returned (or at a rate of one hundred packets per second, whichever is
more) [33].
47 "Power Consumption of Network Devices” Andrew Jess
Using this scheme, it can be shown that each port on the switch would be working at
several times its maximum capacity:
UTL = P × b
UTL = 100 packets/sec × (65515 × 8) bits/packet
UTL = 49.98 Mbps
Where:
UTL = Utilisation one of the switch’s ports in Mbps
P = The number of packets sent per second (minimum value of 100)
b = The number of bits per packet
Since the maximum data rate of each port was 10Mbps, it should be expected that large
amounts of packets would be dropped across the switch. This was confirmed by
checking the status mode (STAT) of the switch, which showed alternating green and
amber lights.
48 "Power Consumption of Network Devices” Andrew Jess
Figure 4.2: Diagram showing the exchange of ping –fs 65507 packets
Using the above scheme it was possible to increase the UTL mode of the switch to ten
LEDs. With reference to Table 4.1, this meant that more than 20Mbps and less than
140Mbps of the switch’s bandwidth were being used.
Figure 4.3: The UTL mode of the CISCO 1900 in “Under Load” mode.
49 "Power Consumption of Network Devices” Andrew Jess
4.3 P R O C E D U R E
First, the power monitor is placed between the plug of the switch and the mains power
and set to the Watts monitoring mode. The router is then placed in its desired “power
state”. For the “Under Load” state, thirty seconds are allowed to elapse to ensure that
network traffic is being transmitted across the switch. Measurements were taken from
the power monitor at intervals of 5 seconds for a total of one minute.
4.4 R E S U L T S
Load State t 0 5 10 15 20 25 30 35 40 45 50 55 60
Idle-Disconnect
14W 14W 14W 14W 14W 14W 14W 14W 14W 14W 14W 14W 14W
Idle 15W 15W 14W 15W 15W 15W 15W 14W 14W 15W 15W 15W 15W
Under Load
16W 16W 16W 15W 16W 16W 15W 15W 16W 15W 16W 15W 16W
Table 4.2 Results of Experiment
Graph 4.1 Results of Experiment
50 "Power Consumption of Network Devices” Andrew Jess
4.5 C H A P T E R S U M M A R Y
The results of the experiment show conclusively that the switch draws more power from
the mains supply whilst under significant load. However, the difference in power draw
between the under-load and idle modes is very small, having a maximum difference of
two watts and occasionally even drawing the same amount. When completely
unplugged from all hosts, the switch consistently drew a lower amount of power,
implying that there is a minimum amount of power required simply to keep the switch
powered on. This means that the overhead required in order to transmit data across a
switch is in the range of one to two Watts.
In the context of a large organisation, one or two Watts per network infrastructure
device is barely discernible in comparison to the power saving potential of other device
types, such as PCs and display devices. This means that although technologies such as
Active Link Rate and Pause Power Cycle can offer power saving potential for network
devices, more effective results could be produced elsewhere.
51 "Power Consumption of Network Devices” Andrew Jess
5 TH E O R E T ICA L POW ER RE Q U IR E M E NT S
O F DATA TR A N S M I S S I O N
5.1 O V E R V I E W
In order to better understand how power is used in existing network devices and
determine what impact any proposed energy-saving schemes would have on them, it is
necessary to appreciate the fundamental power requirements of digital data
transmission. By calculating exactly how much power is required to transmit data it can
be seen whether the transmission of data itself is the main consumer of power in a
network device, or see whether the overheads required to operate other components of
the network device itself are the main consumers. This chapter fulfils the requirements
of Objectives 2 and 4, first investigating theoretical power requirements and secondly
comparing them to results already achieved.
This section will outline the low-level operation of the 10BASE-T technology, which
operates at 10Mbps. Although 10BASE-T may not be considered a “modern”
technology in terms of its throughput and sophistication (especially with the succeeding
100BASE-T and Gigabit Ethernet technologies becoming increasingly available), it has
been chosen to model the power consumption of data transmission for several reasons:
1. Simplicity: By considering one of the first Ethernet technologies, it is possible to
examine the “bare bones” of its operation rather than having to first strip away
any “enhancements” that later versions may have implemented. It will also be
easier to understand the operation of a less elaborate technology.
52 "Power Consumption of Network Devices” Andrew Jess
2. Widespread use: Whilst no longer in as ubiquitous use as it once was, 10BASE-
T ports are still widely available on network devices deployed in today’s
networks. Also, as devices with more advanced interfaces (100BASE-T and
Gigabit Ethernet) are still required to support this technology, it will continue to
maintain a presence within networks for years to come.
3. Relevance to project: As the switching device examined in Chapter 4 contains
almost exclusively 10BASE-T ports, a study of this technology will prove
particularly relevant to any results obtained in this section. As a result, a direct
comparison of theoretical and measured data will be possible.
4. Availability of documentation: The IEEE 802.3 standard contains a wide berth
of information relating to the 10BASE-T technology, its components and
operation. By contrast, the notes on 100BASE-TX and 1000BASE-X can be
considered more as addendums to the simpler 10BASE-T technology, offering
significant enhancements whilst requiring fundamental knowledge of the
underlying technology.
This section, although not representative of all Ethernet technologies currently available,
can be considered to provide a basis for further work in this area. The calculations
performed were made based on thorough research of the Ethernet 802.3 standard and its
related documents. They are entirely theoretical in nature, and although they do
successfully represent results that were recreated in an experimental environment, it
would be advisable to verify the above model before adapting it for any more elaborate
technologies.
53 "Power Consumption of Network Devices” Andrew Jess
5.2 I N T R O D U C T I O N T O T H E PHY
Figure 5.1: The subsystems of the 10BASE-T technology [34]
Figure 5.1 shows an arrangement of the subsystems of the 10BASE-T technology at layer
one of the OSI model (also known as the PHY). Of particular interest are the items
incorporated within the Medium Attachment Unit (MAU). The MAU represents a
collection of further subsystems that are central to the transmission of data over a
particular medium and can be considered analogous to a “transceiver”. In this way, the
MAU and its subsystems are directly responsible for the encoding of data passed from
the Attachment Unit Interface (AUI) into low-level electrical impulses for transmission
across the attached medium.
The MAU itself is further split into two subsystems, the Physical Medium Attachment
(PMA) and the Medium Dependant Interface (MDI).
54 "Power Consumption of Network Devices” Andrew Jess
The PMA acts as an intermediary between the higher level Physical Signalling PLS
system and the medium itself, translating the messages received into a form fit for
transport over the MDI.
The MDI defines exactly how the media used between two MAUs is connected, detailing
items such as male and female connector types, wiring diagrams for these connectors
and specifying transmission and receiving sections of the medium. As far as 10BASE-T
is concerned, the following items are specified:
Connectors: A MAU MDI “connect” interface is defined, specified to accommodate a
connector which resembles (but does not name explicitly) the 8P8C connector which has
become intimately associated with the Ethernet technology.
Wiring & Media Use: Although specified earlier in the standard, it is made explicit here
that 10BASE-T is meant for operation with copper twisted-pair links. Each medium
should contain four pairs of wires, although only two of these pairs are required for this
technology. Two different wiring schemes are specified for the media termination
connectors: One for standard communications, and one “crossover” variety for
connection of devices which operate on the same OSI layer. Individual twisted-pairs are
also identified for particular functions, one for transmission and one for reception:
Figure 5.2: Diagrams detailing straight through and crossover wiring schemes for 10BASE-T [35]. Only
pairs actively used in the transmission/reception of data are portrayed.
55 "Power Consumption of Network Devices” Andrew Jess
5.3 M O D E L L I N G DA T A TR A N S M I S S I O N
5 . 3 . 1 O v e r v i e w
In 10BASE-T, the operation of data transmission can be considered as a series of AC
voltages (in Manchester encoded form) supplied by a transmitting MAU to be
transmitted down an Ethernet segment. This is considered to take place over one
twisted pair of a CAT5 medium (typical of 10BASE-T links), with the remaining active
pair being used for signal reception (as defined in the MDI). The Manchester encoded
symbols are taken to have particular voltage values, and each wire that comprises part
of a twisted pair is considered to have its own distinct resistance (referred to as the
characteristic impedance).
Figure 5.3: The transmission of data, represented as a circuit.
5 . 3 . 2 D a t a E n c o d i n g S c h e m e
10BASE-T Ethernet uses Manchester code as its data encoding scheme. One of the main
characteristics of Manchester encoding is its ability to embed a clock-signal within its
data stream, helping to ensure that both the transmitter and recipient of the data remain
synchronised with each other with a high degree of accuracy. Unlike other encoding
schemes, Manchester code represents each bit of data by a transition, meaning that two
voltage levels are required to represent one bit.
56 "Power Consumption of Network Devices” Andrew Jess
Although offering added reliability and error detection capabilities to the transmission
when compared to other data encoding schemes, this means that Manchester encoding
requires twice many symbols to represent the same amount of binary encoded data
(essentially doubling the bandwidth requirements of the data).
In 10BASE-T Ethernet, the two voltage levels used to represent Manchester encoded
symbols are, on average, 2.5V and -2.5V [36]. As the transition is almost instantaneous
(with the delay between being taken as negligible), a voltage (either positive or negative)
is being transmitted whenever data is being sent.
Figure 5.4: Manchester coding symbols [37]
57 "Power Consumption of Network Devices” Andrew Jess
Figure 5.5: An example of two sample signals in Manchester code, a preamble (0101010) and a full block
of 1’s (1111111)
Although the bottom signal does have considerably more transitions due to the need to
“reset” the cycle to -2.5V at the start of each “1” symbol, it is possible to see that a
constant voltage is being transmitted no matter what the content of the message (due to
0V never being used). As such, these sample signals show that a voltage of 2.5V is
continually applied to the circuit shown in Figure 5.3.
Confusion exists about the voltage levels used by 10BASE-T’s Manchester coding.
Several sources that speak about 10BASE-T Ethernet attempt to define the voltage values
for Manchester encoded signals as 0.85V and -0.85V respectively (including, notably,
Andrew Tannenbaum [38]). However, the 802.3 standard makes no reference to this
figure at all. As such the mean values of 2.5V and -2.5V as shown in the 802.3 standard
are taken as representative of a realistic installation.
58 "Power Consumption of Network Devices” Andrew Jess
5 . 3 . 3 T h e R o l e o f I m p e d a n c e
As an AC circuit simply consisting of two end points, the impedance of the twisted
pair’s individual wires is needed to calculate power use. Impedance is a measure of
opposition to AC signals and can be considered similar to “resistance” in traditional DC
circuits. Impedance is frequency dependant and the frequencies used vary depending
on the technology. In this case, 10BASE-T Ethernet uses frequencies between 5MHz and
20MHz [39].
Suggested CAT5 cable specifications recommend the following impedance values in a
finished product:
“Finished cable shall have a characteristic impedance of 100 ohms ±15% in the frequency range
from 1 MHz to 155 MHz when measured in accordance with ASTM D 4566 Method 3” [40]
[referring to a cable length of up to 100m]
Consequently for the following calculations, the impedance of the medium is taken as
the range of 85Ω to 115Ω at the frequency of 10MHz.
The definition of impedance implies that it is a complex number consisting of both a
magnitude and a phase [41]. However, according the research conducted, the
impedance of CAT5 cabling has been referred to as one particular number (assumedly
its magnitude). As such, the above calculations do not take into account the relative
“phase” of CAT5’s impedance and any effect it may have on power consumption.
59 "Power Consumption of Network Devices” Andrew Jess
5.4 F O R M I N G A CA L C U L A T I O N
Now that all the necessary pieces of information have been gathered from the circuit in
question, it is possible to find an appropriate equation to calculate the power usage of
the circuit. In order to calculate the power requirements of 10BASE-T data transmission,
the following equation is considered, where P equals Power in Watts, V equals Voltage
in Volts and R equals Resistance in Ohms (Ω).
Figure 5.6: A standard power equation
It has been mentioned that the characteristic impedance can be considered similar to
resistance, in a traditional sense. In fact, it has been shown that it is possible to
substitute this value into traditional power equations, such as the above example,
considering it analogous to resistance [41]. And so, by substituting this value into the
above equation, it changes to the following (with the symbol Z representing
characteristic impedance):
Figure 5.7: The same equation, following substitution of characteristic impedance
The Manchester Encoding examples in Figure 5.5 show that no matter what data bits are
transmitted, a constant voltage of 2.5V is being applied to the circuit. This value, along
with the range of possible impedances at the designated frequency (values of 85Ω to
115Ω) was used to calculate the amount of power required to constantly transmit data.
60 "Power Consumption of Network Devices” Andrew Jess
5.5 R E S U L T S
Graph 5.1: Power Consumption of 10BASE-T Ethernet: The results of the equation performed over all
possible impedances
For the range of impedances specified for CAT5 cabling, power values from 54.348mW
to 73.529mW were obtained. These figures represent the power cost of sending data
from one station to another in half-duplex mode. Realistically, stations utilising
10BASE-T will be operating in full duplex mode, doubling the power requirements. As
such, it would be pragmatic to take the power requirements for one port to be in the
range of 108.696mW to 147.58mW.
61 "Power Consumption of Network Devices” Andrew Jess
On a twelve-port switch, such as the CISCO Catalyst 1900 examined in Chapter 4, the
total additional power requirements to facilitate full duplex transmission over all twelve
ports will be in the range of 1.304W to 1.770W. This figure represents just the amount of
power required to enable data transmission and does not take into account any of the
other overheads required by the switch.
5.6 C O N S I D E R A T I O N S
The work performed above is only pertinent to 10BASE-T type Ethernet. Although still
commonly deployed across computer networks, it is important to realise that more
recent, more elaborate technologies are currently leading the market.
Fast Ethernet (100BASE-TX), for example, operates at 100Mbps and could be described
as the de facto Ethernet standard in operation today. Unlike 10BASE-T, it utilises a
different encoding scheme (4B/5B), meaning that the voltage levels used to represent
data bits would be different. It is also expected that as more data is being transmitted by
this technology that power requirements would rise.
Further to this, Gigabit Ethernet (1000BASE-T) is likely to become increasingly popular
as computer systems yearn for more and more bandwidth. Again, its encoding scheme
differs from its predecessors, using PAM-5 encoding to allow the transmission of four
symbols in parallel [38]. This increased throughput would be likely to be reflected in the
power usage of the technology, increasing it significantly.
Some articles [42] refer to a non-standard 1W per port target that Gigabit Ethernet ports
aspire to achieve, around ten times the power requirements of a 10BASE-T port. From
this it can be seen that as the data rate of a technology increases, so will its power
requirements.
62 "Power Consumption of Network Devices” Andrew Jess
Also of note is the emergence of Power-over-Ethernet switches. As the ports from these
devices are expected to provide a considerable amount of power via the connected
CAT5 cabling (around 13W via 802.3af), the power requirements of devices that offer
this capability will be significantly higher.
As such, the results calculated for 10BASE-T should not be taken as entirely conclusive
or as particularly up to date, as a plethora of other widely used technologies may prove
to have wildly different requirements. These further technologies could make for
interesting further study on this subject, however.
5.7 C H A P T E R S U M M A R Y
5 . 7 . 1 C o n c l u s i o n s
From the results obtained from these calculations, it can be seen that the task of data
transmission using 10BASE-T does not actually require much power at all. Only one or
two Watts would be required to both transmit and receive data on a twelve-port switch,
an immaterial amount of power compared to the overheads required to actually operate
the switch.
Although power savings at this low level may be relevant to, for example, portable
battery powered devices (where every Watt matters when attempting to increase battery
lives) the savings garnered by forcing mains-powered devices to be more efficient at the
data encoding level will prove miniscule. Consequently technologies such as Pause
Power Cycle (discussed in Chapter 2), although novel and effective at reducing power by
small amounts, may not be worth the detrimental effects they introduce to network
traffic.
63 "Power Consumption of Network Devices” Andrew Jess
5 . 7 . 2 C o m p a r i s o n t o O b t a i n e d R e s u l t s
The results obtained from these calculations are consistent with those observed and
recorded in Chapter 4. Despite as much load as possible being put on the 12-port
network switch, the power reading was only observed as increasing by one watt at the
most, making the results of these calculations viable. If it were possible to completely
consume all available bandwidth, it would be expected to see this power consistently lie
around 2 Watts higher than its idle-disconnect mode.
Due to the resolution of the readings provided by the power monitor used (which took
power readings to the nearest full Watt), it was not possible to compare the jumps in
power consumption in any great detail: for future iterations of Chapter 4’s experiment, it
would be desirable to locate a power monitor that could measure power changes down
to the mW.
64 "Power Consumption of Network Devices” Andrew Jess
6 P O W E R CO N S U M P T I O N A NA LY S I S F O R T H E UN I V E R S I T Y O F T H E W E S T O F S C OT L A N D
6.1 O V E R V I E W
This chapter outlines a case study of power consumption throughout a typical
organisation with a medium-to-large IT installation. A thorough investigation of many
device types was undertaken in order to gain a broad picture of how power is used (and
in what amounts) across the organisation, satisfying Objective 1 of the project.
The first step towards conducting a study on typical organisational power consumption
was to choose an appropriate organisation. Several requirements were outlined:
1. The organisation studied must be large enough to have a considerable outlay
in Information Technology so that a large enough footprint could be
measured.
2. The organisation must not be so expansive as to prevent an accurate snapshot
of this footprint being taken.
3. Devices must be physically available for power-consumption readings, with
an ideal scenario possessing frequent contact with an individual in the
position to acquire information from.
It was decided early in the project that the University of the West of Scotland would
satisfy the first requirement: a University campus requires constant connectivity for
both staff and students internally, as well as upholding a public presence on the
Internet. It was clear that the IT infrastructure of the campus was an elaborate and
intricate installation. The presence of the School of Computing in the University added
to the conception that there would be a wide and varied set of devices deployed across
its network.
65 "Power Consumption of Network Devices” Andrew Jess
The University itself consists of four separate campuses: one each in Paisley, Hamilton,
Ayr and Dumfries. These campuses’ IT installations are all interconnected, allowing
communication over a vast geographical distance. Each campus is also connected to an
off-campus data centre where large amounts of data are stored and served.
In order to satisfy the second requirement, the scope of the study was reduced to the
Paisley campus alone. It was clear that an extensive study into the power requirements
of the inter-campus network would be out with the time constraints of this project.
Requirement 3 was able to be satisfied as well: student labs and classrooms provided
ample equipment for readings to be taken from, and assistance from the IT Services
team at the University provided information about some of the more opaque aspects of
the network that would have been otherwise inaccessible.
6.2 C H O O S I N G A M E T H O D O L O G Y
In order to complete the study within the time constraints of the project, it was deemed
impractical to create a unique methodology to model the power consumption of the
campus. To satisfy both time constraints and provide the most accurate portrayal of the
University’s network, an existing methodology developed for measuring organisational
power consumption would be used. Thus, before any practical readings were taken in
the campus, an analysis of existing power consumption studies was performed.
The main requirements of a suitable study would be to first of all be relevant to the
University’s range of devices, and second of all be resilient to adaptation by this project.
An additional concern would be the resilience to estimation, should completely accurate
figures and measurements be unavailable.
66 "Power Consumption of Network Devices” Andrew Jess
Upon initial research, it seemed there was little work dedicated to analyse how much
power network devices use. Rather, many power consumption studies were carried out
with much wider scope, generally focusing on the power consumption of an entire
country, or in smaller cases, single data centre installations. A selection of relevant
literature is evaluated below.
6 . 2 . 1 “ E n e r g y C o n s u m p t i o n b y O f f i c e a n d T e l e c o m m u n i c a t i o n s
E q u i p m e n t i n C o m m e r c i a l B u i l d i n g s ” b y R o t h e t a l . ( 2 0 0 2 )
6 . 2 . 1 . 1 O V E R V I E W
The 2002 publication on the energy consumption of office and telecommunications
equipment by Roth et al. (hereafter referred to as Roth, for simplicity) consists of a 211
page study which examines the Annual Electricity Consumption (AEC) of a range of
office equipment categories. Its broad scope encompasses many items of interest to this
project including personal computers, server computers, display devices, printers and
computer network equipment but also discusses the impact of other devices such as
uninterruptable power supplies (UPS), copiers, telephone networks, et cetera.
Chart 6.1: AEC of all Office Equipment (Roth) [1]
67 "Power Consumption of Network Devices” Andrew Jess
Its analysis of office equipment’s AEC ratings found that network infrastructure
equipment used a comparatively small amount of power compared to other office
equipment. Chart 6.1 shows that computer networks and their associated devices only
use 6.4TW-h (terawatt hours) of the total 97TW-h consumed by office equipment in the
year 2000 (6.6%).
However, Roth did identify network infrastructure devices as an area worthy of further
investigation, devoting an entire section of their study to their impact. Notably, Roth
subdivides the area of network infrastructure equipment into distinct device types,
considering hubs, switches (both LAN and WAN) and routers as separate areas.
Traditional LAN equipment was shown to use the majority of power in this area with
hubs, LAN switches and routers claiming 6TW-h (6.4%) of power consumption figures.
More specialised equipment such as Cable Modem Termination Systems, Remote Access
Servers and WAN switches were also shown to have a comparatively small (3.6%)
combined contribution to power consumption.
Chart 6.1 also shows the impact that PC and server computers have on energy
consumption (over 30% combined). As these devices are can be considered as endpoints
on a network, their power consumption is also relevant to this project. Likewise,
printers are often connected to modern networks and as such their 5.9% contribution can
be considered as worthy of investigation.
Below, a sample of Roth’s study is examined in order to gauge its appropriateness for
this project. The section chosen details Roth’s calculations of the AEC of network
infrastructure devices.
68 "Power Consumption of Network Devices” Andrew Jess
6 . 2 . 1 . 2 S A M P L E A N A L Y S I S : N E T W O R K D E V I C E S
Chart 6.2: AEC of Network Infrastructure Devices (Roth) † [1]
Network Hubs
AECHUB = N× Pport × tOH
Figure 6.1: Roth’s hub AEC calculation
Network hubs were shown to use 25% of the total network infrastructure device AEC
figure. Roth’s methodology for measuring the AEC of hubs consisted of calculating a
watt per port value for each device (Pport). An average power draw value for the entire
device would be taken and then be divided by the number of ports present on the
device. The resulting value would allow larger capacity devices which used more
power to be compared fairly to smaller, less energy consuming ones.
† Figures are subject to rounding
69 "Power Consumption of Network Devices” Andrew Jess
Despite this attempt to levelling the playing field, Roth’s findings showed that larger
capacity devices used a lower amount of power per port, with an 84-port hub using
1.23W/port, while a 96-port hub used only 1.13W/port. Both hubs were from the same
manufacturer.
In order to calculate the AEC of the hub, a generous value for Pport was used (1.25W) to
account for the variety of hub models deployed across the country. This value was then
multiplied by industry estimates for the number of ports installed in all commercial
buildings in the United States (N) and multiplied by the number of hours in operation
per year (tOH). In his calculations, Roth realised the necessity of computer networks
being available at all times. As such, his operational hours are always taken to be the
“always on” value of 8,760 hours per year. The resulting value of these calculations
could be considered the AEC value of the all hubs in the country.
AEC of LAN Switches
LAN Switches were shown to use 52% of the total network infrastructure device AEC
figure. A similar method was used to calculate the AEC of these devices, with Roth’s
findings showing that switches tend to use more power per port than hubs, with an
average Pport value being taken as 4W.
70 "Power Consumption of Network Devices” Andrew Jess
AEC of Routers
AECROUTER = N× PAV × tOH
Figure 6.2: Roth’s router AEC calculation
Routers were shown to use 17% of the total network infrastructure device AEC figure.
Roth used a different methodology for calculating the AEC of these devices. As routers
do not generally have as many ports installed as switches and routers, a power per port
value would be misrepresentative. Instead, he simply considered an average power
draw for a typical router (PAV, taken as 40W) and multiplied that by an estimated
number of routers in operation (N) and the same constant tOH value of 8,760 hours.
AEC of WAN Switches, Cable Modem Termination Systems & Remote Access Servers
AECWAN = N× P × tOH
Figure 6.3: Roth’s WAN Switch AEC calculation
These devices collectively represented 3.6% of the total network infrastructure device
AEC figure. The first of these, WAN Switches are used to manage WAN traffic, with a
typical application being the aggregation of DSLAM (itself multiplexed DSL traffic [1]
traffic for ISPs.
Roth touched only briefly on the methodology used to calculate the AEC of WAN
switches. He abstracts the stock of devices into a number of “shelves”, representing the
typical method of distribution among vendors. A simple power measurement is taken
as representative of all devices here. Again, the concept of always-on computing is
represented by tOH being taken as 8,760.
71 "Power Consumption of Network Devices” Andrew Jess
The method of calculating Cable Modem Termination Systems and Remote Access
Servers was not discussed in his report.
6 . 2 . 1 . 3 F I N D I N G S
Roth’s analysis of network devices identifies LAN switches as the largest consumers of
electricity in the network infrastructure device area. Since the number of hub ports and
switch ports is very similar (93.5 million hub ports [28] to a mean of 92,500,000 switch
ports †) , the main reason for this is the fact that Roth’s investigations showed that
switch ports tend to use more than three times as much power as hub ports.
One disadvantage of Roth’s report was the amount of estimation required in gathering
an inventory of each type of device. Because the scope of the study was so huge
(calculating AEC values for devices deployed across all of the United States), the margin
of error in estimating amounts of devices would no doubt be considerable.
The sources Roth cited in his estimations also tended to be published comparatively far
apart. His estimations for hub ports were based on a report carried out by Silva in 1998
whilst his switch port estimates were gathered over 1999 and 2000. It would be expected
that a lot more hub ports would be installed over 1999 and 2000, something his AEC
calculations should reflect. As a result, Chart 6.2 should show an increased proportion
of power being consumed by hubs.
Of additional concern, the power per port values calculated for all of these devices
would be gathered from only one or two different models of device. This abstraction
fails to represent the diversity of devices deployed across the country. As such, his
power per port values could be misrepresentative of the country’s actual average.
† Studies showed a range of 90,000,000 [29] to 95,000,000 (ADL Estimate based on [29])
switch ports in operation in 1999/2000
72 "Power Consumption of Network Devices” Andrew Jess
However, Roth’s methodology would be extremely accurate if used in a context where
exact inventory, power draw and model types of network devices were known. This
study also contains useful measurements for considering the contribution of workstation
PCs and servers and would allow a diverse analysis of the University’s power usage to
be made.
6 . 2 . 2 " C a s e s t u d y o f d a t a c e n t e r s ’ e n e r g y
p e r f o r m a n c e " b y S u n & L e e ( 2 0 0 5 )
6 . 2 . 2 . 1 O V E R V I E W
In 2005, Sun & Lee examined in detail the power consumption of two data centres and
found them to be facilities that consumed large amounts of energy [30]. Interestingly,
they noted that the energy requirements of data centre floor space (per m2) could exceed
that of traditional commercial office space by eighteen times †.
Sun & Lee’s study differed from Roth’s considerably, most notably in that the devices
examined were abstracted considerably more. Also present was a more detailed
examination of lighting circuits and heating, ventilation and air conditioning (HVAC)
systems which were only briefly touched on in Roth’s study. They considered the data
centre to have four broad areas of power consumption:
† Commercial office space typically measured 50W/m2 to 110/m2 while data centre power
demand had a much wider range of 120W/m2 to 940W/m2 [30].
73 "Power Consumption of Network Devices” Andrew Jess
Area Description
IT Equipment Defined by Sun & Lee as “servers, data storage,
network devices, monitors, etc” [30], the devices
which provide services to users.
UPS Loss The wastage of power directed into the
Uninterruptable Power Supply. Whilst giving
power redundancy to all devices they are
connected to, UPS efficiency varies greatly.
HVAC As IT Equipment generates a lot of heat in its
operation, facilities are required to regulate the
temperature of a room and ensure its proper
ventilation.
Lighting The energy impact of overhead lighting used by
staff in the data centres.
Table 6.1: Sun & Lee’s Device Criteria
This study also asserts the conception of “always on” computing, with both data centres
showing that their IT equipment (along with supporting HVAC and UPS devices) were
kept powered on 24 hours a day, seven days a week [30]. Only lighting equipment was
powered on or off on a scheduled basis, dictated by its occupancy.
74 "Power Consumption of Network Devices” Andrew Jess
The major findings uncovered from Sun & Lee’s study was that supporting the
operation of IT Equipment often consumed more energy than the IT Equipment itself.
Chart 6.3 below shows a breakdown of the entire energy consumption of a data centre
that they examined. From this we can see that just over a quarter of data centre power
usage supplies the devices themselves, and that the remainder of energy is used in
providing stable operating conditions for devices (HVAC), visibility for users (Lighting)
and redundancy of the power supply in case of failure (UPS).
Chart 6.3: Breakdown of energy use of a data centre (Sun & Lee) [30]
Sun & Lee made several recommendations on how to reduce energy expenditure in data
centres. Most of these suggested the reconfiguration of the support services to be more
efficient. They reinforced the necessity of keeping the ratio of support services cost to IT
Equipment cost as low as possible by saying “Generally, a larger contribution from the IT
equipment to the total energy use indicates a better overall energy performance” [30]. No
recommendations were made on limiting the operation of IT equipment (such as turning
off or suspending workstations when not in use).
75 "Power Consumption of Network Devices” Andrew Jess
6 . 2 . 2 . 2 F I N D I N G S
Several criticisms can be made of Sun & Lee’s study which could question the reliability
of their conclusions. The first item of note is that both data centres were located in
Singapore. Due to the tropical nature of the temperatures in this country, coupled with
the fact that their study was carried out in the middle of summer, it could be suggested
that HVAC systems would be much more abundant in this country (and more under
load at this time) to keep the temperature of the data centres at an operable level.
Consequently, a similar data centre located in a more temperate region could see the
HVAC contribution decreased.
Sun & Lee’s methodology in measuring power consumption between the two data
centres could also be seen as slightly misleading. The metrics for graphing both centres’
energy use failed to take the floor space of the facility into consideration. Considering
that data centre 1’s total floor space was 97m2 and data centre 2’s floor plan was more
than ten times that at 1048m2, different HVAC and UPS requirements for larger premises
might explain the seeming “inefficiency” of data centre 2.
Sun & Lee also make no differentiation between network infrastructure devices and
workstation computers. Indeed judging by their definition, even printers, monitors,
projectors and scanners could be included in the final energy measurements. This
meant that no real conclusions regarding the power consumption of network devices
could be made.
It would be interesting to see Sun & Lee’s methodology put to use in a larger range of
data centres. In this report, only two facilities were investigated. However if the trend
of IT Equipment’s energy consumption being over shadowed by support services was as
consistently high as shown in Chart 6.3, then seeking to increase HVAC and UPS
efficiency would perhaps be a more worthy task.
76 "Power Consumption of Network Devices” Andrew Jess
6.3 C O N C L U S I O N S & C H O S E N M E T H O D O L O G Y
Roth’s methodology for the AEC calculations of Office and Telecommunications
Equipment has been identified as the most appropriate choice. It offers the flexibility to
analyse a range of devices present on a network and includes a detailed examination of
network infrastructure devices. The methodology, although broad in scope, offers the
potential to be scaled down for the purposes of this project. With its heavy bent towards
estimation, it would also be forgiving if complete data for the University could not be
obtained.
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6.4 O U T - O F - S C O P E A R E A S
6 . 4 . 1 O v e r v i e w
A number of device types have been omitted from the following study, originating from
Roth’s report, the report examined by Sun & Lee, or items observed on the University’s
network.
The reasons for omission vary depending on the area, but largely are a combination of
irrelevance to the area of network power consumption and the time constraints imposed
by the project.
While none of these devices would take up a particularly significant segment of any
results gained, in more detailed future study it may be advisable to implement them.
However, it must be mentioned that each of the areas below will impact on the power
consumption figures of the organisation studied: Investigations made in the future
focusing on the energy conservation of office equipment or the efficiency of data centres
should take note of these areas and implement them.
6 . 4 . 2 F r o m R o t h ’ s S t u d y
Supercomputers
Knowledge of or access to a supercomputer in the University could not be gained.
Magnetic Disk Storage Systems
Knowledge of or access to these systems in the University could not be gained.
Copy Machines
Copy machines cannot be truly considered as part of the University’s computer
network, often being stand-alone devices for independent use. Also, their use in the
University is perhaps not as ubiquitous as in the offices that Roth’s report is based on.
78 "Power Consumption of Network Devices” Andrew Jess
Uninterruptable Power Supplies
Although most certainly deployed in the University (most likely in combination with
server computers, to provide power redundancy in event of a disaster), they are not in
themselves network devices. They take up only a small portion of Roth’s report,
accounting for only 5.8% of office equipment energy usage.
Telephone network equipment
Since the University does not yet utilise VoIP for its telephony network, this section is
irrelevant to the University’s computer network deployment.
6 . 4 . 3 F r o m S u n & L e e ’ s S t u d y
HVAC Systems
Although essential in supporting the network’s infrastructure devices and undoubtedly
a factor in the financial upkeep of these services, Roth’s study treats HVAC systems as
out of scope and of “considerable complexity”, and for the same reason this study will
do the same. Sun & Lee’s study does examine these systems in considerable complexity,
so reference to their study is recommended if knowledge on this area is required.
Lighting
Although mentioned in Sun & Lee’s methodology and considered a major contributor to
the power footprint of a data centre, the investigation of the cost of lighting was not
deemed relevant to the objectives of this project.
79 "Power Consumption of Network Devices” Andrew Jess
6 . 4 . 4 F r o m t h e P a i s l e y C a m p u s N e t w o r k
Wireless Access Points
Wireless connectivity in the University, although accessible at several points throughout
the University, cannot be considered as fully functional. Also, the locations of access
points and the deployed number of these devices would be fully unknown, as most are
hidden out of plain sight.
Intrusion Prevention Systems (IPS) / Intrusion Detection Systems (IDS)
These devices are not acknowledged in Roth’s report, nor were they available to take
readings from. Although they do impact slightly on the network’s power usage, they
are considered outside the scope of this report.
Storage Area Networks
Similarly to IPS and IDS devices, these are not acknowledged in Roth’s report, nor are
they readily accessible to take readings from. Although they do impact slightly on the
network’s power usage, they have been excluded from this report for simplicity’s sake.
80 "Power Consumption of Network Devices” Andrew Jess
6.5 I M P L E M E N T A T I O N O F M E T H O D O L O G Y
6 . 5 . 1 S u m m a r y o f R e s u l t s
Chart 6.4: AEC Consumption for the University of the West of Scotland, Paisley Campus
Using Roth’s methodology, the resultant study estimates that the Paisley campus of the
University of the West of Scotland consumes approximately 1229MW-h of electricity per
year in order to keep the University’s network operational. It is worth noting that if the
out-of-scope areas noted in Section 6.4 were taken into account, the actual power usage
of the campus would be slightly higher.
81 "Power Consumption of Network Devices” Andrew Jess
The most significant contributors to the University’s power expenditure are
undoubtedly the PCs and workstations that necessitate the network’s existence,
comprising over a third of energy consumption (485.35 MW-h). This is not surprising,
as there are in excess of two thousand machines connected to the network, a large
proportion of which remain powered on continuously.
In order to provide around-the-clock connectivity to the many services offered by the
network, the underlying network infrastructure equipment must also be continually
powered. These devices are not limited to those access layer switches connected to end-
user workstations, but also take into account core switching and routing functions. This
requirement to provide constant connectivity is represented by a considerable power
outlay: network infrastructure devices utilise approximately another third of the total
power consumption (418.49 MW-h).
The remaining third of power used in the University’s network is split between three
further areas: the monitors and displays which accompany every PC (150.50 MW-h),
printers connected to the network (97.99 MW-h) and server machines which provide the
network’s internal and external services (76.91 MW-h).
The remainder of this chapter is split into sections each representing a sector of Chart
6.4. Within each section is a description of the devices examined, how the stock of each
device type was obtained, how the typical operating hours for each piece of equipment
were calculated and the typical power requirements of each device type. Finally,
calculations detailing the AEC of each device type are made, along with any relevant
accompanying observations. Any recommendations that could curtail the consumption
of energy on the campus are appended to these observations.
Concluding this section is a comparison of the results of this study with those obtained
by Roth in his report.
82 "Power Consumption of Network Devices” Andrew Jess
6 . 5 . 2 P e r s o n a l C o m p u t e r s ( P C s )
6 . 5 . 2 . 1 B A C K G R O U N D
The desktop computer is one of the most ubiquitous elements of an organisation’s
network. Indeed, the computer networks were originally developed to facilitate the
sharing of information between computers. As the personal computer can be considered
as a network device itself (referred to as “building blocks” [31] of a network), an
investigation of the power consumed by typical machines is of interest when gauging an
entire organisation’s network’s power usage.
6 . 5 . 2 . 2 A E C C A L C U L A T I O N F O R P C S
Stock of Devices
Figure 6.4: Deployment of Staff PCs across Paisley Campus
83 "Power Consumption of Network Devices” Andrew Jess
Figure 6.5: Deployment of Student PCs across Paisley Campus
Stocks of machines distributed across the campus were obtained from a representative
of IT Services (included as Appendix E). These figures include computers contained
within student accessible laboratories as well as staff computers connected to the
University network. It should be stressed that only computers connected to the network
could be accounted for and that an unknown amount of non-networked workstations
were likely to exist. However, as this study concerns itself only with the power
consumption figures for the campus’s network, the numbers obtained were adequate.
84 "Power Consumption of Network Devices” Andrew Jess
Usage Times
An exchange with IT Services disclosed that there was no power conservation plan in
place for student lab workstations on the campus’s network. Individual power schemes
of machines did not include instructions to place machines into lower power schemes
after a certain amount of time had elapsed. Likewise there were no plans to power
down PCs over holidays and other periods of no use. As such, the times for “standby”
and “off” modes were taken as 0 hours per year.
Speaking with security staff of the University revealed that student lab machines are
never powered down, even when the labs are closed. Taking this into account, student
machines were assumed to be powered on and in active mode for 8760 hours per year.
Staff machines were assumed to be on for as long as staff members were in the
University, and powered off otherwise. Since a wide range of working hours exist for
the various faculties, 2,610 hours annually was taken as a generous estimation for each
machine (ten hours per weekday).1
Type of Machine Active (S0) Standby (S3) † Off (S5) Unplugged (“S6”)
Student 8760 0 0 0
Staff 2610 †† 0 6150 0
Table 6.2: Usage times per power mode, per PC (hours/year)
† Roth’s report made distinctions between standby and suspend modes. Since the
computers in the campus use neither of these modes for any length of time, they have
been combined as “Standby (S3)”.
†† 261 weekdays in 2010
85 "Power Consumption of Network Devices” Andrew Jess
Power Draw
For student lab machines, two types of PC were considered, standard specification lab
machines and the higher end workstations contained in high performance labs. An
average for the power consumption of each of these machines was used to one student
machine. Staff machines were taken as being of standard lab machine specification. The
power draw information below has been reapportioned from Chapter 3.
Type of Machine Active (S0) Standby (S3) Off (S5) Unplugged (“S6”)
High Spec Lab (Optiplex GX620)
79.37W 2W 2W 0W
Standard Spec Lab (HP dc7900 SFF)
31.11W 2W 2W 0W
Average 55.24W 2W 2W 0W
Table 6.3: Power draw of typical PCs in each power mode
86 "Power Consumption of Network Devices” Andrew Jess
AEC Totals
Type of Machine
Installed Base
Mode Use (h/year)
Draw (W)
Annual AEC (MW-h)
Student 684 Active (S0) 8760 55.24 330.9892416
Off (S5) 0 2W
Staff 1,651 Active-Processing (S0) 2610 31.11 154.3637121
Off (S5) 6150 2
Total 485.3529537
Table 6.4: AEC Calculation for PCs
Chart 6.5: AEC of Personal Computers
87 "Power Consumption of Network Devices” Andrew Jess
6 . 5 . 2 . 3 C O N C L U S I O N S
PCs and workstations in the University are estimated to use around 485MW-h per year.
The most evident observation that can be made by the figures gathered are that despite
being almost three times fewer in number, student PCs located throughout the
University consume more than twice as much power. One of the reasons for this is that
a portion of student machines themselves are higher consumers of power than staff
machines with their more humble specifications. However, the main reason for the
sheer amount of power being consumed is due to their hours of operation; being kept in
active mode throughout the year (even throughout the night!) results in a vast increase
in electricity usage.
A recommendation that can be made from examining this data is that a power-policy
should be implemented on student machines in the University as soon as possible. By,
for example, putting machines into standby when student labs close at night†, the
annual AEC of student PCs could potentially be reduced to 171.49MW-h, a saving of
almost half!
As discussed in the literature review, there are technologies emerging that promise a
means of being able to remotely control the power status of devices; CISCO EnergyWise
being given as an example. By harnessing a technology such as this, it may be possible
to automate the process of powering machines down at the end of each night,
effortlessly saving the University large sums of money on its energy bills.
† ACPI S3 mode for 12 hours per night
88 "Power Consumption of Network Devices” Andrew Jess
6 . 5 . 3 M o n i t o r s
6 . 5 . 3 . 1 B A C K G R O U N D
Monitors are essential companion devices to PC installations throughout the University.
Without them, the PCs would lack their main means of communication with users. The
monitor and PC are often treated as one combined unit from a retail perspective, but due
to their individual power requirements, this report treats them as distinct entities.
In the past, monitors were most always of the Cathode Ray Tube (CRT) type [1]. Now,
with more affordable LCD displays available (and the increased picture quality and
space saving that these units provide) CRT units are being gradually replaced. The
upgrade of monitors has a sound economic backing as well, with a study showing that
between monitors of the same size, CRT devices can use up to three times as much
power when active [43].
6 . 5 . 3 . 2 A E C C A L C U L A T I O N S F O R M O N I T O R S
Stock of Devices
It was assumed that in the University, each PC had an accompanying monitor. Only
monitors of the 17” LCD specification could be found in the University at the time of
writing, so this type of device was taken as standard.
In summary, the total stock of monitors on campus was taken as 2,335 17” LCD units.
89 "Power Consumption of Network Devices” Andrew Jess
Usage Times
To gain exact usage data for monitors over the campus, an extensive usage study would
be required. In Roth’s report, figures from various other authors are cited for office hour
usage times of various types of equipment. However, this data is geared towards 9am
to 5pm office usage and is inappropriate for this study.
Usage data for used in this study was taken to mimic that of PCs: it was assumed that
each student monitor was in active use for the 12 hours per day that labs were
accessible, while being put powered down into suspend mode or being powered off for
the remaining 12 hours. Staff monitors were assumed to be on for ten hours per
weekday and in off/standby mode for the remainder of time.
Power Draw
Five different power modes were specified for monitors:
Power Mode Description
Active On and in use
Standby Screensaver mode
Suspend Screen in sleep mode
Off Soft off: Power supply still
connected
Unplugged Power supply removed from
mains
Table 6.5: Description of Monitor Power Modes
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Power consumption measurements were taken with a power monitor for each of these
modes.
Type Active Standby Suspend Off Unplugged
17” LCD 20.25W 21W 0W † 0W 0W
Table 6.6: Power draw of monitor in various modes†
Due to the similarity of power consumption values between several power modes, it
was possible to simplify power consumption into two modes: Since “Suspend”, “Off”
and “Unplugged” modes all provided a measurement of 0W, they are combined into a
“Suspend/Off” mode for the purposes of the AEC calculation. Likewise, since the
“Active” and “Standby” readings are so similar, they have been averaged and treated as
a single “Active” mode with a value of 20.625W.
† Readings gained from monitor in suspend mode were shown as 0W. This suggested that the
power monitor used was not sensitive enough to measure the tenths of Watts that were likely
being consumed. Assumedly if the reading was 0.5 or above, the power reading would have
been rounded up to 1W. Since this implies that the power drawn in suspend mode was 0.4W or
less, this reading can be considered negligible and has been taken as 0W.
91 "Power Consumption of Network Devices” Andrew Jess
AEC Totals
Stock Mode Draw (W) Usage (h/year) AEC (MW-h)
17” LCD (Student)
684 Active 20.625 4,368 61.621560
Suspend/Off 0 4,368
17” LCD (Staff)
1651 Active 20.625 2610 88.87539375
Suspend/Off 0 6150
Total 150.49695375
Table 6.7: AEC of Monitors
Chart 6.6: AEC of Monitors
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6 . 5 . 3 . 3 C O N C L U S I O N S
Calculations estimate that LCD monitors across the University campus consume in
excess of 150MW-h per year. Monitors attached to staff machines utilise more power,
despite having a dramatically lower usage pattern. This can be attributed to the larger
stock of staff machines.
Actual power usage is bound to be less than this as the University’s power scheme
requires monitors to power into Suspend mode after 30 minutes of inactivity, making
the 12 hour active use estimate per monitor rather generous.
The replacing of older CRT monitors throughout the University (performed prior to and
throughout the year of this report, so comprehensively that a CRT monitor could not be
found for measurements) has proven to be a wise decision, with Roberson’s study
suggesting that power consumption may have been reduced by up to three times!
Interestingly, measurements showed that monitors with a screensaver active utilised
more power than those in active use. A speculated reason for this could be due to the
brightness of the screen in each mode. The screensaver rendered a black screen with a
small logo, meaning that most pixels would have had to be rendered black. The active
monitor on the other hand rendered mostly bright colours. This suggests that LCD
monitors require more power to render dark pixels than light pixels resulting in systems
using dark screensavers being slightly less efficient.
93 "Power Consumption of Network Devices” Andrew Jess
6 . 5 . 4 P r i n t e r s
6 . 5 . 4 . 1 B A C K G R O U N D
To any paper based company or organisation that uses IT in its day-to-day operations,
printers are essential pieces of equipment. They allow forms that have been generated
and filled in electronically to be converted to hard copy for filing or correspondence. It
comes as no surprise then that printers are common across the University, used not just
by administrative staff for functions similar to traditional business requirements, but
also for teaching staff and students (who often have high volumes of paperwork to print
themselves).
There are many different types of printer available in today’s market, but the University
primarily uses two types of printer:
Laser Printers: Tending to be large units for high-volume, high-speed and communal
use within the University, these devices utilise xerography (similar to copy machines)
but differ in that the image is produced by the scanning of a laser across a blank sheet of
paper. Smaller model types are also in use, appropriate for individual use in a staff
member’s office, for example.
Inkjet Printers: Almost exclusively small, desktop sized models appropriate for small
scale personal printing. To produce their image, minuscule jets of toner are propelled
onto a blank sheet of paper. In the University, these are commonly installed alongside a
staff member’s PC in their office.
94 "Power Consumption of Network Devices” Andrew Jess
6 . 5 . 4 . 2 A E C C A L C U L A T I O N S F O R P R I N T E R S
Stock of Devices
Figure 6.6: Deployment of Staff Printers across Paisley Campus
95 "Power Consumption of Network Devices” Andrew Jess
Figure 6.7: Deployment of Student Printers across Paisley Campus
The figures for the stock of printing devices were obtained from data that IT Services
was able to provide (attached as Appendix F). As with PCs, only printers determined to
be “on the network” are counted.
The distribution of printers in the University network is surprisingly asymmetrical. The
printers utilised by staff on the network outnumbers that of the students’ by a factor of
four at least. This seems strange until the required applications of each group are
considered: Staff printers are likely to be small inkjet printers placed on or near the staff
member’s desk whilst student printers will always be large laser printers placed in labs
or central locations for communal access.
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The 36 student printers are taken to be a mix of medium and large laser printers (the HP
Laserjet 4250tn and HP Laserjet 9050n devices, respectively), the former typical of
classroom laboratories where individual classes take place and the latter widespread in
the larger open access labs, capable of dealing with high volumes of requests.
In order to find out the distribution of inkjet-to-laser printers in the University, a survey
was conducted amongst a selection of the University’s staff: 24 members of staff were
asked how they typically printed documents in the University.
Chart 6.7: Distribution of printer use across staff
Detailed results of the survey are included as Appendix G.
From these results, it can be established that 11 out of 24 (approximately 46%) of staff
used communal laser printers to print their documents. The remaining 13 out of 24
(approximately 54%) staff members said that they had a printer in their office with seven
of these being inkjet printers and six of these being laser.
97 "Power Consumption of Network Devices” Andrew Jess
This means that seventeen out of twenty-four staff members use laser printers (71%) and
seven use inkjet printers (29%). When applied to the stock of staff printers in the
University, these percentages have been applied. This means that of the 159 staff
printers total, approximately 46 are inkjet printers whilst the remaining 113 are laser
printers.
The inkjet printer chosen to represent the 46 devices present on the network was taken
as the HP Deskjet 880c model. A mix of large, medium and small laser printers (the HP
HP Laserjet 9050n, HP Laserjet 4250tn and Laserjet P2055d devices, respectively) have
been considered to represent the deployment of devices across the staff network. This
displays the desktop laser printers revealed in the survey, and medium to large
communal devices available for both teaching and administrative staff.
Usage times
Usage times for student printers were based from the operational time of student labs:
The continual supply of power to student PCs inferred that printers received the same
treatment. From this, the time for the printers being in off mode was taken as 0.
The power saving capabilities of the laser printers examined by this report allowed them
to power themselves down to suspend mode after an hour of inactivity. It was
presumed that they remained in this mode for the 12 hours they remained inaccessible
to students (labs are typically closed from 9pm to 9am).
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The large printer examined (a HP Laserjet 9050n) provides a top speed of 50 pages per
minute. This means that even to cope with the printer’s reported load of around 27
pages per operating hour †, the actual time spent in Active mode will remain extremely
small each day. The printer’s datasheet (attached as Appendix H) claims the minimum
time to deliver a first page is 8 seconds. Generously estimating that each of these 27
pages per hour is a distinct job means that the printer is only active for 216 seconds per
hour (or 2592 seconds per operating day). This means that the printer is active for 0.72
hours per operating day (262.8 hours per year), spending the remainder of its time in
standby mode. It is presumed that the printers are active enough not to go into suspend
mode during the day.
Staff laser printers, being largely communal are expected to have similar usage patterns
to student ones. Also, the variance in staff schedules means that communal printers
would require relatively flexible access, so the same operating hours have been taken as
for student labs.
Individual inkjet printers located in staff offices were assumed to have similar usage
patterns to staff PCs and monitors, being turned on for a total of ten hours per weekday.
Thirty minutes of this time was taken as a generous estimate for active printing time.
The remaining time was taken as “off”.
Undoubtedly all staff laser printers would not be of the same size as student communal
printers. In order to reflect this and portray fairly the range of device types elicited by
the survey, average power draws between small, medium and large laser printer models
are used in AEC calculations. It is felt this helps to provide a more accurate AEC value
for staff printers.
† Following data taken from a typical printer’s usage report:
Time in operation: Since October, 2007 (approximately 823 days) (Time of writing 9th Feb 2010)
Lifetime sheets printed: 270,062 (Usage page)
12 operating hours/day
27.345 pages per hour
99 "Power Consumption of Network Devices” Andrew Jess
Power Draw
Roth’s report recognises several different authors’ attempts to identify the various
power states of laser printers. These include three modes (Active/Ready, Standby/Low
and Off) by Meyer & Schaltegger and four modes (Active/Ready, Standby/Low, Suspend
and Off) by Macebur. Roth’s chosen methodology was to follow Kawamoto et al.
(2001)’s approach by taking only two power modes, Active/Ready (to represent a printer
that is powered on awaiting print orders) and Off, which represents a printer that is
powered off and adding an additional 1W-h per image created by the printer. This
method could apply only to laser printers, as Roth acknowledges:
“We did not apply the energy/image methodology to inkjet printers because the 1W-h/sheet
energy consumption comes from studies of electrostatic reproduction energy consumption (e.g.,
Nordman, 1998), which is germane to copiers and laser printers but not the inkjet printing
process.” [1, p.62]
As this study did not have usage data for the number of images printer for each
individual laser printer, Macebur’s four-attribute approach (Active/Ready,
Standby/Low, Suspend and Off) was chosen instead. The inkjet printer chosen did not
have a suspend option available to it, so only Active, Standby and Off modes are shown
for this device.
Power Mode Description
Active Where the printer is actively printing
a document.
Standby Where the printer is powered on and awaiting
print orders, but is not actively printing.
Suspend An approximation of S3 mode where
the printer is in a power saving state.
Off Where the printer is powered off, but is
still connected to the power supply
(with phantom load in effect).
Table 6.8: Power states of printers
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Power usage readings for each printer have been taken from datasheets from each
model type. (Datasheets for the large, medium, small and inkjet printers used are
included as Appendices H, I, J and K respectively). Datasheet readings were compared
against actual power draw for one of these models and deemed to be accurate.
In order to represent the power draw of a typical laser printer, the draws of different
sized devices were taken and averaged. For inkjet printers, they were treated as one
device model.
Printer Type Mode Draw (W) Staff AVG Student AVG
Active Large Laser 1000
750W 840W
Medium Laser 680
Small Laser 570
Typical Inkjet 30
Standby Large Laser 205
77.667W 112.5W
Medium Laser 20
Small Laser 8
Typical Inkjet 5
Suspend Large Laser 36
19W 24.5W
Medium Laser 13
Small Laser 8
Typical Inkjet n/a
Off Large Laser 0.3
0.333W 0.3W
Medium Laser 0.3
Small Laser 0.4
Typical Inkjet 5
Table 6.9: Typical and average power draws for printers
These average readings were then used in calculating the AEC of all printing devices
within the University.
101 "Power Consumption of Network Devices” Andrew Jess
AEC Totals
Printer Type Installed Base Mode Draw (W) Usage (h) AEC (MW-h)
Laser Printer (Student)
36 Active 840 262.8 7.947072
Standby 112.5 4117.2 16.674660
Suspend 24.5 4380 3.863160
Off 0.3 0 0
Total 28.484892
Laser Printer (Staff)
113 Active 750 262.8 22.272300
Standby 77.667 4117.2 36.1340746812
Suspend 19 4380 9.403860
Off 0.333 0 0
Total 67.8102346812
Inkjet Printer (Staff)
46 Active 30 130.5 0.140940
Standby 5 2479.5 0.446310
Off 5 6150 1.107000
Total 1.69425
Subtotal 97.9893766812
Table 6.10: AEC of Printers
Chart 6.8: AEC of Printers
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6 . 5 . 4 . 3 C O N C L U S I O N S
In total, printing devices are estimated to use approximately 98MW-h of power
annually. Owing to the larger stock of staff printers, these devices make up the majority
of this figure at almost 75%.
When split by type, laser printers make up the majority of the inventory of devices
present on the network. Since the University has need for large capacity, high-speed
printers, inkjet devices would not be appropriate to fill this role. However as a
consequence of using these higher-powered devices, the power consumption of this
device type has risen dramatically. In this case, the lower stocks of inkjet printers, and
the fact that they use around twenty times less power than small laser printers give an
explanation for their relatively small segment of power consumption.
103 "Power Consumption of Network Devices” Andrew Jess
6 . 5 . 5 S e r v e r C o m p u t e r s
6 . 5 . 5 . 1 B A C K G R O U N D
The University’s network requires a wide array of server computers to store student and
staff data as well as provide connectivity from the Internet (in the form of a publicly
accessible website and external access to student webmail, amongst others).
The University utilises blade servers in order to provide these services along with
several traditional rack mounted server devices. Blade servers are streamlined versions
of traditional rack mounted servers, with many of their components being either
removed or made more efficient in order to provide a modular design. The advantage
of this can be considered the saving of valuable rack space in server rooms, making
attached servers more energy efficient.
Rather than having their own distinct power supplies like the traditional rack mounted
servers, the individual blades are all mounted into a central chassis which manages
power distribution amongst all blades. The chassis itself can accommodate anywhere
from one to four power supplies (with more supplies permitting the configuration of
load bearing between them, as well as providing redundancy should one supply fail).
104 "Power Consumption of Network Devices” Andrew Jess
6 . 5 . 5 . 2 A E C C A L C U L A T I O N F O R S E R V E R S
Stock of Devices
With data provided from IT Services, the server devices deployed on the University
network comprised of the following:
Model Installed base Description/Purpose
IBM X3850M2 1 Exchange Disaster Recovery Server
IBM X3650 2 Internet Security & Acceleration (ISA) Servers
1 Media Server
1 CISCO Management Server
1 Nortel Management Server
IBM BladeCenter HS21 8 Individual blades
IBM BladeCentre H Chassis 1 The 8 HS21 blades are mounted on and receive their power from this chassis.
Table 6.11: Server Distribution across University
Usage times
It was assumed the University’s servers operated 24 hours a day, 365 days a year (8760
hours) in order to provide constant service to network users.
Power Draw & AEC Totals for Rack Mounted Servers
Roth’s report differentiates between four types of server based on their assumed
lifespan. Since this report examines the power usage of servers that are currently in use
on the campus, these categories were treated as one. For this study, a separate
distinction was made: that between the blade server installation, and the rack mounted
servers, since the method of calculating their AEC was slightly different.
105 "Power Consumption of Network Devices” Andrew Jess
The rack servers in use by the University had various rated power supplies on their
nameplates. These figures represent the maximum power draw of the device, not its
every day power draw. A study performed by Hipp in 2001 showed that the actual
power draw of a server is on average, a ratio of 51% of its nameplate value [44].
Datasheets showing the rated power supplies are attached as Appendices L and M.
Device Installed Base Nameplate Draw (W)
Typical Draw (W)
Usage (h/year) AEC (MW-h)
IBM X3650 5 835W 425.85W 8760 18.652230
IBM X3850M2 1 1440W 734.4W 8760 6.433344
Table 6.12: AEC of Rack Mounted Servers
Power Draw & AEC Totals for Blade Server Installation
Calculating the power consumption of the blade server installation simply required
calculating the power usage of the blade centre chassis, since any devices mounted to it
(including the 8 HS21 blades) would draw their power from this. Correspondence with
IT Services in the University relayed that it was not possible to find out how much
power was being drawn from each of the chassis’ installed power supplies. It was also
uncertain whether Hipp’s study would be applicable to this device, as his study
predated the introduction of the blade server paradigm. However, IT services also
implied that it was impossible for each of the chassis’ power supplies to be consistently
pulling its nameplate value, so Hipp’s model was tentatively applied.
A datasheet showing the power information for this chassis is attached as Appendix N.
Device Installed Base
Power Supplies
Nameplate Draw (W)
Typical Draw (W)
Usage (h/year)
AEC (MW-h)
BladeCenter H Chassis
1 4 2900 1479 8760 51.824160
Table 6.13: AEC of Blade Server Installation
106 "Power Consumption of Network Devices” Andrew Jess
6 . 5 . 5 . 3 C O N C L U S I O N S
Chart 6.9: AEC of Server Devices
The server computers deployed across the University’s network are estimated to use
approximately 77MW-h of power per year. Amongst these servers, it can be seen that
the blade server installation consumes the most power, at two thirds of the total AEC.
Approximately one third was utilised by the six stand alone rack servers currently in
use. The five IBM X3650 servers appear to be fairly low powered in comparison to the
single IBM X3850M2, this no doubt being due to the latter server’s increased
specifications requiring a larger power supply.
It should be noted that although responsible for the largest amount of power
consumption in this scenario, the blade centre chassis has the potential to be more power
efficient than the rack servers in use: With a capacity of fourteen blade bays, its chassis
will become more efficient compared to these traditional servers as the number of blades
installed increases. For this reason, blade servers are recommended for large
installations that require the majority of its bays to be filled with blades.
107 "Power Consumption of Network Devices” Andrew Jess
6 . 5 . 6 N e t w o r k I n f r a s t r u c t u r e E q u i p m e n t
6 . 5 . 6 . 1 H U B S
Reason for omission
Hubs are devices that connect several network devices together, treating them as though
they were connected to the same cable segment. Hubs do not perform any management
of packets that come in through its ports; rather they simply broadcast received frames
from all ports except from the one the frame was received on. Hence, each of the devices
connected to the hub would be a part of the same “collision domain” where the
efficiency of a network can be impacted by devices trying to transmit frames
simultaneously. They operate solely at the Physical layer of the OSI model, Layer 1.
Very few (if any) hubs are still in operation in the University’s network. This is largely
due to the increasing availability and affordability of access layer switching options
which provide more a more efficient way to interconnect devices. The calculation of the
hub’s impact on this network has therefore been omitted. Consequently, it is likely that
the power footprint of the University’s switching devices will be proportionately larger
than shown in Roth’s study.
6 . 5 . 6 . 2 S W I T C H I N G & R O U T I N G
Background
Although switches provide similar connectivity and network functionality to network
hubs, they are considerably more sophisticated and as a result offer increased
performance. Access-layer switches operate at the second layer of the OSI model, the
Data-Link layer, allowing active management of frames that pass through them. One
benefit of this is that each connection created between hosts on the switch become part
of their own collision domain, ensuring that other traffic passing through the switch will
not interfere (or cause collisions with) their communications.
108 "Power Consumption of Network Devices” Andrew Jess
The CISCO hierarchal model defines three “layers” of switching and routing that should
occur in a typical LAN. The access layer of the model defines switches which connect
directly to end-user devices. These switches always operate at Layer 2 of the OSI model
and usually contain 12, 24 or 48 ports in order to service an entire room or floor of a
building.
The distribution layer of the model traditionally included LAN based routers and more
sophisticated network switches that operate at Layers 2 and 3 of the OSI model. Today,
these tasks can be integrated into existing core level devices by installing specialised
modules into them, simplifying the topology of the network. For this reason, this layer
is considered along with the core switching layer for the purposes of this study. The
routing of traffic between different sub-networks and Virtual LANs (VLANs) also
happens at this layer.
At the core of the hierarchal model are routers and Layer 3 switches. This layer can be
considered the backbone of the network and concerns itself solely with speed and
reliability; ensuring packets are transmitted from one portion of the network to the other
as fast as possible. No packet manipulation (such as the implementation of Access
Control Lists) is performed at this level. As all traffic on the network has to pass
through this layer, devices are frequently configured with high redundancy in mind.
There also exists a final class of switch known as the WAN Switch. These devices
concern themselves with the delivery of data over large geographical distances and are
often used by ISPs to distribute services such as DSL. These devices are not covered in
the AEC calculations as it is the Paisley campus’s network alone (and not its links to
other campuses) being examined in this report.
109 "Power Consumption of Network Devices” Andrew Jess
AEC Calculation for Access Layer Switches
Stock of Devices
The exact number of access level switch devices deployed across the campus is
unknown and unrelated to their AEC value. Instead, a power per port value is required.
An approximate number of ports required to service the University’s devices can be
deduced simply, since each network-enabled device (PCs and printers) would require
one port on an access level switch. The number of ports deployed in this case is the sum
of these devices, a total of 2530 ports.
Usage times
In order to provide ceaseless connectivity to the network, it was assumed the
University’s access layer switches operated 24 hours a day, 365 days a year (8760 hours).
Power Draw & AEC Totals
In order to calculate the amount of power consumed by all switches deployed across the
network, the amount of power a single port uses must be known. Two main models of
switch have been deployed across the University: The Netgear FS728TP and the Nortel
4548GT-PWR. In order to achieve an accurate value for access layer switching, the
power-per-port value for each switch was calculated and averaged, before applying to
the number of ports deployed across the network.
A datasheet displaying the Netgear switch’s power draw is attached as Appendix O.
Power draw information from the Nortel switch was read directly from its supply.
Switch Type Maximum Power Consumption (W) Ports per device Power per port (W)
Netgear FS728TP
225 24 9.375
Nortel 4548GT-PWR
580 24 24.167
Average Power Per Port
16.771
Table 6.14: Power-per-port for Access Layer Switches
110 "Power Consumption of Network Devices” Andrew Jess
Ports Deployed Average Power per port (W)
Usage (h) AEC (MW-h)
2530 16.771 8760 371.6923188
Table 6.15: AEC of Access Layer Switches
Although the figure of 371.69MW-h seems rather high, it must taken into account that
these switches are all capable of delivering Power-over-Ethernet and offer the potential
to provide expansion possibilities to the University by facilitating easy installation and
powering of devices such as VoIP phones, security cameras and wireless access points.
Note that figure cited for number of ports deployed may be slightly inaccurate due to
there being an unknown number of wireless access points connected to the network.
AEC Calculation for Distribution Layer Switching, Core Switching & Routing
Stock of Devices
Correspondence with the IT Services at the University revealed that the distribution
layer of the University’s switching scheme has been condensed into the core switching
layer. The central switch at the core level has a series of line card modules installed in
order to provide this function. Therefore, all devices present at the distribution layer are
contained within those for the core layer.
The core layer of the University’s switching scheme consists of two Layer 3 CISCO
Catalyst 6509-E devices. One of these is kept on cold standby, meaning it has no impact
on the network’s power footprint.
The task of routing can be described as the connection of one or more networks or sub-
networks. This task was traditionally performed by devices called routers, which
operate at Layer 3 of the OSI model. Complex rules and configuration arrangements
allow the sophisticated management of traffic that pass through them.
111 "Power Consumption of Network Devices” Andrew Jess
In the University, however, separate devices are not required to perform routing duties.
The core layer switch discussed above provides routing functionality between the
different VLANs and sub-networks of the University’s network. Two extra CISCO ASA
5580-40 devices are employed to enable routing between the internal network, the
Internet and the intermediary Demilitarized Zone (DMZ).
In summary, only one active Catalyst 6509-E and a pair of CISCO ASA 5580-40 devices
are active at this layer.
Usage times
Again, to provide uninterrupted network connectivity, it was assumed the University’s
access layer switches operated 24 hours a day, 365 days a year (8760 hours).
Power Draw & AEC Totals
The active Catalyst 6509-E switch, much like the BladeCenter chassis, utilises multiple
power supplies to increase redundancy and enable load balancing (two 6000W
nameplate rated supplies). IT Services was able to provide running power draw figures
for both of these supplies, simplifying calculations and providing increased accuracy
that estimation might have sacrificed. This information forms Appendix P.
With reference to the CISCO ASA 558-40 data sheet (attached as Appendix Q), these
devices are estimated to draw around 800W. The AEC of the ASA 5580-40 pair
represents the power required to provide additional routing functionality to the network
and is shown on Chart 6.10 as “other routing”.
112 "Power Consumption of Network Devices” Andrew Jess
Device Installed Base
Power Supplies
Nameplate Draw (W)
Typical Draw (W)
Usage (h) AEC (MW-h)
Catalyst 6509-E
1 (Active) 2 6000 2671.2 8760 23.399712
6000 2671.2 8760 23.399712
Total AEC 46.799424
Table 6.16: AEC of Catalyst 6509-E
Device Model Installed Base Typical Draw (W) Usage (h) AEC (MW-h)
CISCO ASA 5580-40 2 800 8760 14.016000
Table 6.17: AEC of CISCO ASA 5580-40 devices
113 "Power Consumption of Network Devices” Andrew Jess
6 . 5 . 6 . 3 C O N C L U S I O N S
Chart 6.10: AEC of Switching & Routing devices
The network infrastructure devices deployed in the University are estimated to use
around 418MW-h per year. Comparing the results of the implementation of Roth’s
methodology upon network infrastructure devices with his original publication, it is
clear to see that network topologies have changed considerably. In Roth’s original
publication, he noted large amounts of power consumption from both network hubs and
dedicated routers.
By comparison, hubs are non-existent in the University’s network. Cheap switching
options (and the improved efficiency of such devices) have provided sufficient to
essentially antiquate these devices. Routing, too, is no longer the domain of the
dedicated device: One sufficiently powerful Layer 3 switch proves powerful enough to
provide all core switching and VLAN routing tasks, something that would previously
have taken several separate devices. Even the cluster of CISCO ASA 5580-40s that
provide additional routing are not dedicated devices: they also provide additional
security features in addition to their routing tasks.
Finally, as in Roth’s study, LAN switches are shown as still having the most impact on
the power consumption of the University’s network.
114 "Power Consumption of Network Devices” Andrew Jess
6.6 C O M P A R I S O N T O O R I G I N A L S T U D Y
6 . 6 . 1 O v e r v i e w
Chart 6.11: A comparison of the current study with Roth’s 2002 report.
Comparing the performed study with Roth’s original study performed in 2002, it can be
seen that although there are several inconsistencies in the proportions of power
consumed, there are also several similarities between the data sets:
115 "Power Consumption of Network Devices” Andrew Jess
6 . 6 . 2 P C s & W o r k s t a t i o n s
Whilst PCs and workstations use just under a third of the total AEC of the five device
types in Roth’s report, this study sees an increase in power consumption by these
devices. A likely explanation for this is the inclusion of higher specification PCs in this
report which although use more efficient power supplies than those in Roth’s report,
also use more power in general. Roth’s report also uses a considerable sum of gathered
usage data to gauge the operational times of the PCs in his report. In contrast, most of
the PCs examined in this report were almost constantly powered on.
6 . 6 . 3 M o n i t o r s
A vast reduction in power use by monitors and display devices has occurred between
2002 and 2010. In Roth’s study, monitors used far and beyond the most power out of the
devices he examined, whilst in this study usage has been reduced to around an eighth of
the total AEC figure. The most likely reason for this is the comprehensive upgrade of
CRT monitors to LCD screens, resulting in a lower power usage per unit, yielding
massive savings in energy.
6 . 6 . 4 P r i n t e r s
The proportion of power consumed by printers in both this study and in Roth’s original
study is extremely similar, with both segments weighing in at about a twelfth of the total
AEC figure. This suggests that printers have remained relatively unchanged in the
eight years that have passed between the studies.
Roth’s figure may be slightly over-stated in comparison, as he also includes impact
printers and line printers in his study, both of which had no relevance to this project.
116 "Power Consumption of Network Devices” Andrew Jess
6 . 6 . 5 S e r v e r C o m p u t e r s
Server computers in Roth’s report use around twice as much power compared to the
devices examined in this report. Only one blade enclosure (with eight blades) and six
stand alone rack servers were examined in this report, whilst Roth’s deals with an entire
country’s stock of server devices. This could contribute to this inconsistency.
The increased efficiency of blade servers and their utilisation of only one power supply
combined with these results could suggest that today’s server devices are becoming
more efficient and economical than past devices.
6 . 6 . 6 N e t w o r k I n f r a s t r u c t u r e D e v i c e s
The network devices section of the chart shows a massive increase between 2002 and
2010. Devices under this category account for almost three times the proportion of
power claimed in Roth’s report. Roth’s lack of investigation into the different varieties
of switch device could perhaps account for this deficit, as his report assumed all switch
devices were of the common access layer variety, ignoring the impact of the significantly
higher powered core and distribution layer switches.
117 "Power Consumption of Network Devices” Andrew Jess
6.7 C H A P T E R S U M M A R Y
This chapter represents an extensive study on the power usage of network devices in the
University of the West of Scotland’s Paisley campus, satisfying Objective 1 of the project.
Existing methodologies for power consumption measurements were investigated and
the most appropriate one chosen. This was then altered in accordance with the needs of
the University’s campus, allowing accurate and representative data to be collected and
presented to give a comprehensive breakdown of just how much power is utilised by the
University’s network.
With due observation of the results, it is clear to see that there are several ways in which
the University can reduce its financial outlay on electricity. Indeed, in one way the
University already has: the replacement of aging CRT monitors with power-efficient
LCD equivalents will reduce the amount of power consumed by display devices by up
to three times.
However, by adopting a power management system to automate the shut-down of
computers located in student accessible labs, much more power could be saved. It is for
this reason that this report recommends the adoption of such a scheme.
In conclusion, it is hoped that the results of this chapter provide a clear overview of the
University’s power expenditure, and that they may be of assistance to its administrators
when considering the financial worth of “greening” the campus’s IT operations.
118 "Power Consumption of Network Devices” Andrew Jess
7 CRITICAL EVALUATION
7.1 C O M P L E T I O N O F O B J E C T I V E S
O b j e c t i v e 1
Chapter 6 comprehensively covers the power requirements of the Paisley Campus of the
University of the West of Scotland within the scope defined. It is hoped that the data
obtained is of some use to the University itself in reducing its electricity expenditure.
O b j e c t i v e 2
Chapter 5 attempts to produce a valid theoretical underpinning for the power
requirements of 10-BASE-T Ethernet, creating a mathematical model to calculate the
results shown. These results did appear feasible, although seeming surprisingly low.
Objective 5 goes on to confirm the validity of the model developed.
O b j e c t i v e 3
Chapters 3 and 4 both explore the effects of “load” on network devices from two
perspectives: The effect of a network enabled PC’s processing load on power
consumption, and the effect of a network infrastructure device’s network load on power
consumption. This objective’s outcomes solely consisted of collecting the data through
experimentation, with Objective 5 making comparisons between this data. The
successful completion of both experiments can be considered tantamount to its success.
119 "Power Consumption of Network Devices” Andrew Jess
O b j e c t i v e 4
A section of Chapter 5 is dedicated to comparing the theoretical power requirements
calculated against those observed through experimentation in Chapter 4. The results
gained through the mathematical model developed did match up correctly with the
results gained through experimentation, suggesting that they are valid. Although
perhaps not as long as any of the other objectives, there was not much more to explore in
this area beyond what was said.
O b j e c t i v e 5
Objective 5 consisted of taking the results gained in Chapters 3 and 4 and making
comparisons between data gained. The investigation of Chapter 3’s results ascertain that
ACPI modes closer to “S6” gain maximum power savings whilst large amounts of
processing load can almost double power consumption. Chapter 4 surprisingly notes
that the power requirements of data transmission are extremely low, with most power in
a typical switch being used in device overheads. Overall conclusions for this objective
prove surprising, revealing that controlling the power modes of host PCs may prove to
be a more worthy endeavour than making network switches more efficient.
120 "Power Consumption of Network Devices” Andrew Jess
7.2 A R E A S O F C O N C E R N
Several problems and concerns encountered throughout this project should be noted:
1. The first problem encountered by this project lay in the choice of switching
device for Chapter 4. At first, a low-powered wireless router was chosen with
four Ethernet ports. This device first of all did not produce enough power to
observe a notable difference with network traffic being piled on it and second of
all, did not support anywhere near enough hosts to produce such traffic. This
issue was documented in considerable detail in the Interim Report. The eventual
solution was to select a higher powered CISCO Catalyst 1900 switch, which used
more power and supported three times as many hosts.
2. The power monitor used did not perhaps go into as much detail as desired,
displaying results only to the nearest Watt. Although acceptable results have
been gained, future projects may wish to use a higher resolution device.
3. Although the results of Chapter 5 (Objective 2) do compliment the experimental
results gained in Chapter 4, it is uncertain whether the mathematical model
developed was technically correct or elaborate enough to conclusively support.
The main reason for the difficulty in creating this model lay in not having the
correct skill sets or subject background in the area of electronics. Although many
meetings were held with project supervisors and external advisors (who
provided as much support and guidance as possible), the level of understanding
was perhaps just too far out of reach for a humble Honours project.
121 "Power Consumption of Network Devices” Andrew Jess
4. The two advanced objectives chosen (Objectives 4 and 5) certainly did not
require as much work as the basic ones, seeming instead to be brief addendums
to the other objectives. This suggests that the project was perhaps slightly flawed
at the Project Brief level. Given the opportunity to revise this document,
Objectives 1 and 2 would have been better considered as Advanced Objectives,
considering the level of understanding and research required, as well as the
amount of work necessary to complete them.
In summary, the complexity of this project was not realised until the Project Brief had
already been submitted. Objectives stated in the document should have been more
clearly defined, ensuring that those requiring the most work should be considered
advanced. Ensuring the resilience of the Project Brief is advice that could not be
stressed more strongly to students considering an Honours level project.
7 .3 P R O J E C T MA N A G E M E N T
The management of this project can be considered very good, overall.
All deliverables were completed before their designated deadlines. Both the Interim
Report and the final Dissertation were completed in advance of the submission date.
Experimentation was spread throughout both trimesters, with Chapter 3 being
completed before the submission of the Interim Report (admittedly with lower
resolution results), and Chapter 4’s experimentation being left until the beginning of
Trimester 2. Data gathering for the University power study (Chapter 6) was obtained
through a combination of meeting with IT Services personnel, online research and
individual investigation into device types, being collected over two trimesters.
122 "Power Consumption of Network Devices” Andrew Jess
All management meetings were attended with minutes being drawn up immediately
afterwards, in most cases. On a couple of occasions, the agenda for these meetings were
perhaps submitted without much notice. However, on every occasion they were
submitted prior to the meeting itself.
Worthwhile advice to future students would be to take note of how long pulling
together the final dissertation takes. This project was worked on modularly, in most
cases with most objectives consisting of their own documents. Although a highly
recommended way to work, one should not underestimate how time consuming
formatting and proofreading a document can be.
7.4 F U T U R E W O R K
Chapter 5 of this project perhaps offers an introductory overview of the power
consumption of Ethernet technologies. A particularly ambitious Computer Networking
student in years to come may wish to expand on it, particularly to explore the impact of
increased data rates on power consumption. Certainly, such an investigation may even
be worthy of an individual practiced in the discipline of Electronic Engineering. It
should be noted that information regarding this area could not actually be located whilst
performing the project’s research: Endeavouring to expand this objective could no
doubt be considered novel work suited for a level higher than this project.
Based on the foundation lain here, an inter-campus study of the University’s power
consumption would be a worthwhile endeavour. Particularly as the University is
attempting to lower its energy footprint at the moment, it would be interesting to see
whether the power requirements of the campus have decreased. Investigating the
power requirements of the links between campuses would also be fascinating.
123 "Power Consumption of Network Devices” Andrew Jess
7.5 S U M M A R Y
This project has attained all of its objectives, providing a comprehensive insight into
several pertinent issues regarding the power consumption of network devices. The
results obtained through some sections of this project have also produced a variety of
interesting conclusions, resulting in a range of recommendations that could be made to a
host of networking professionals.
Overall, it is felt that the project was performed to a satisfactory standard. The work
involved in its completion was extremely rewarding with the entire experience not only
being an enjoyable experience, but also having a profound effect on myself as a student.
124 "Power Consumption of Network Devices” Andrew Jess
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Access Method and Physical Layer Specifications" (Figure 14-1, p315)
[35] IEEE (2008) "802.3-2008 Part 3: Carrier sense multiple access with Collision Detection (CSMA/CD)
Access Method and Physical Layer Specifications" (p. 343-344)
[36] IEEE (2008) "802.3-2008 Part 3: Carrier sense multiple access with Collision Detection (CSMA/CD)
Access Method and Physical Layer Specifications" (p. 357)
[37] IEEE (2008) "802.3-2008 Part 3: Carrier sense multiple access with Collision Detection (CSMA/CD)
Access Method and Physical Layer Specifications" (Figure 7-10, p.133)
[38] Tannenbaum, A (2002) "Computer Networks” Fourth Edition (p.275, 289) Prentice
Hall
[ISBN: 0130661023]
[39] Fairhurst, G (2007) “Manchester Encoding” Aberdeen University
[Accessed 20:00, 22nd April 2010 at: http://www.erg.abdn.ac.uk/users/gorry/course/phy-
pages/man.html]
[40] Wireville (2003) “Suggested Generic Cat 5 Specification”
[Accessed 20:00, 22nd April 2010 at: http://wireville.com/news/news11.html]
[41] NDT Resource Center (date unavailable) "Impedance"
[Accessed 20:00, 22nd April 2010 at: http://www.ndt-
ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/impedance.htm]
[42] Van Bavel, Callahan et al. (2004) "Voltage-mode line drivers save on power"
EETimes
[Accessed 20:00, April 22nd 2010 at:
http://www.eetimes.com/showArticle.jhtml?articleID=51200238]
[43] Roberson et al. (2002) “Energy Use and Power Levels in New Monitors and Personal Computers”
(p.16) Energy Analysis Department, University of California
127 "Power Consumption of Network Devices” Andrew Jess
[44] Hipp, C. (2001) “Less is More”, presented by Chris Hipp of RLX Technologies
E-Source HiDEL Summit, 1 May, Broomfield, CO.
128 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X A : P R O J E C T B R I E F
COMP10024: Computer Networking 4 Project Project Brief Student Name: Andrew J. Jess Matriculation #: B00113374 Supervisor: D. Thomson 2nd Supervisor: F. Clark Session: 2009/2010 Project Title: Power Consumption of Network Devices Overview
As energy prices rise in a world of economic uncertainty, companies have started to look to energy-saving practices and technologies in order to reduce their power-related expenses. Aside from being financially advantageous, this also allows companies to pursue a more “green” method of operation, reducing their impact on the environment in regards to their carbon footprint and production of greenhouse gases. As such, the amount of power that network infrastructure devices consume plays a major part on the bottom line of their energy bills. This project will initially investigate fundamentally, the theoretical requirements of data communications. From there, the power consumption of a selection of network infrastructure devices (switches, routers, bridges and hubs), servers and host systems will be examined through the observation of a model network. Finally, an investigation into the financial requirements of an organisation's network infrastructure (in the context of power-expenses) will be explored. Objectives
The basic objectives of this project are:
Investigate the costs involved in maintaining the operation of a typical organisation's IT infrastructure
Investigate and calculate the theoretical power requirements of data transmission.
Observe and measure the power consumption of devices in a typical network, both under load and whilst idle.
The following advanced objectives will also be achieved:
129 "Power Consumption of Network Devices” Andrew Jess
Compare and analyse observed, real-life power usage data against
theoretical projections. Compare the power usages of idle devices with those under load.
Initial Reading List
Data and Computer Communications: 4th Edition (W. Stallings) Advances in Computers Vol. 75: Models & Metrics for Energy-Efficient Computing (P. Ranganathan et al)
Energy Consumption by Office and Telecommunications Equipment in Commercial Buildings - Volume I: Energy Consumption Baseline (K. Roth et al) Report to Congress on Server and Data Center Energy Efficiency (U.S. Environmental Protection Agency)
Ethernet Alliance: Energy Efficient Ethernet (Various Authors) Various white papers outlining proposals accepted by the IEEE 802.3az Task Force aiming to reduce energy consumption by Ethernet enabled networking equipment.
Resources
Access to a computer lab containing the following:
o Range of network devices including (but not limited to) switches, routers, bridges, hubs.
o Computer systems, both of a host and server nature. o The appropriate media to interconnect these devices
Access to a plug-in power-meter (or other device capable of gathering
power consumption data)
Approval
Student Supervisor 2nd Supervisor Coordinator
Signature:
Date:
130 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X B : O P T I P L E X GX620 DA T A S H E E T
131 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X C : H P D C 7 9 0 0 S M A L L F O R M F A C T O R D A T A S H E E T
132 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X D : C I S C O C A T A L Y S T 1 9 0 0 D A T A S H E E T
133 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X E : E S T I M A T E D S T O C K O F S T U D E N T & S T A F F P C S
Student Lab PC's
Staff PC's (Estimated)
C block 10
A block 243 E block 148
B block 50
F block 34
C block 50 H block 12
D block 85
Open Access J 132
E block 140
J block 233
E block south 105
L block 36
F block 80 N block 75
G block 65
Student Union 4
H block 133
J block 264
TOTAL 684
K block 18
L block 120
M block 160
N block 43
S block 10
T block 45
Watt 10
Smiley 20
TBC 10
TOTAL 1651
These figures were obtained from a spreadsheet provided by a representative of IT
Services, November, 2009
134 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X F : E S T I M A T E D S T O C K O F S T U D E N T & S T A F F P R I N T E R S
Student network printers
Staff Network Printers
B block 1
A block 60
C block 3
B block 6
E block 4
C block 6
F block 4
D block 6
G block 1
E block 14
H block 2
F block 3
J block 14
G block 5
L block 3
H block 12
N block 4
J block 6
K block 4
TOTAL 36
L block 3
M block 23
N block 2
P block 1
R block 2
S block 3
Watt 3
TOTAL 159
These figures were obtained from a spreadsheet provided by a representative of IT
Services, November, 2009
135 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X G : S T A F F P R I N T E R D I S T R I B U T I O N S U R V E Y
Following are the results of the survey conducted via email for staff members of the
School of Computing in February, 2010. For confidentiality reasons names are not
included, having been replaced instead with “Respondent 1, Respondent 2” et cetera.
==========================
Staff printer distribution
==========================
-----------------------------
Communal Laser Printer Users
-----------------------------
NAME COMMENT
Respondent 1: Prints out on communal Laserjet
Respondent 2: Prints out on communal Laserjet
Respondent 3: Sends documents to a communal laser jet printer
Respondent 4: Uses communal laser printer
Respondent 5: Network printer (Laser)
Respondent 6: Staff mono laser, admin colour
Respondent 7: shared printer in H121 (HP LaserJet 4250)
Respondent 8: larger printer in communal area
Respondent 9: laser printer in H332
Respondent 10: communal shared printer in E267
Respondent 11: test centre has HP Laserjet P2015n
Respondent 12: printer in E267 for bigger jobs
Respondent 13: communal printer in E267
Respondent 14: network printer in E-block [E267, i suspect]
Respondent 15: laser printer in E215 shared by three people,
Respondent 16: laserjet in E267 for large/duplex
Respondent 17: printer in E267 if large job
TOTAL COUNT: 17 (6 duplicate)
--------------------------
136 "Power Consumption of Network Devices” Andrew Jess
Individual Printer Users
--------------------------
Respondent 18: Laser printer for sole use (HP laserjet P2055d)
Respondent 19: Has Epson stylus photo 830 for small/colour jobs
Respondent 20: Small inkjet in office
Respondent 21: laser printer in office
Respondent 22: cartridge epson in office
Respondent 23: small office lasetjet
Respondent 24: laser printers in office (HP Laserjet 4250tn, 3600n)
----------------------------------------------------------------------------
Respondents who use both Communal Laser Printers & any private printer
-----------------------------------------------------------------------------
NAME COMMENT
Respondent 4 Has a laser printer in his room (HP Laserjet 2100)
Respondent 6: Deskjet in his office
Respondent 12: inkjet (HP Deskjet 880c) in office for small jobs
Respondent 15: plus one inkjet
Respondent 16: HP deskjet 880c in office for small/colour;
Respondent 17: laser printer in office (ELP-6200)
Total number of respondents: 24
...who use communal laser printers: 17
...who use any type of private printer users: 13
...who use both communal laser printers and any type of private printer: 6
...who use private inkjet users: 7
...who use: 6
137 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X H : H P L A S E R J E T 9 0 5 0 N D A T A S H E E T
138 "Power Consumption of Network Devices” Andrew Jess
The original four page data sheet has been truncated here. The above selections show
only those parts relevant to the project.
If required, the original document can be located at the following URL:
http://h10010.www1.hp.com/wwpc/pscmisc/vac/us/product_pdfs/410000.pdf
139 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X I : H P L A S E R J E T 4 2 5 0 T N D A T A S H E E T
The original four page data sheet has been truncated here. The above selection shows
only the part relevant to the project.
If required, the original document can be located at the following URL:
http://www.vcbm.com/files/HP_4250_Series_Brochure.pdf
140 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X J : H P L A S E R J E T P 2 0 5 5 D D A T A S H E E T
The original two page data sheet has been truncated here. The above selection shows
only the part relevant to the project.
If required, the original document can be located at the following URL:
http://h10010.www1.hp.com/wwpc/pscmisc/vac/us/product_pdfs/LJ_P2055d.pdf
141 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X K : HP DE S K J E T 880C DA T A S H E E T
A selection of the website where the datasheet is displayed is shown above. The above
selection shows only the part relevant to the project.
If required, the original document can be located at the following URL:
http://h10025.www1.hp.com/ewfrf/wc/document?docname=bpd06092&tmp_task=prodi
nfoCategory&lc=en&dlc=en&cc=us&product=61607#N4431
142 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X L : IBM X 3650 DA T A S H E E T
A selection of the website where the datasheet is displayed is shown above. The above
selection shows only the part relevant to the project.
If required, the original document can be located at the following URL:
http://www-03.ibm.com/systems/uk/x/hardware/rack/x3650/specs.html
143 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X M : IBM X 3850 M 2 DA T A S H E E T
A selection of the website where the datasheet is displayed is shown above. The above
selection shows only the part relevant to the project.
If required, the original document can be located at the following URL:
http://www-03.ibm.com/systems/x/hardware/enterprise/x3850m2/specs.html
144 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X N : B L A D E C E N T E R H C H A S S I S D A T A S H E E T
A selection of the website where the datasheet is displayed is shown above. The above
selection shows only the part relevant to the project.
If required, the original document can be located at the following URL:
http://www-03.ibm.com/systems/bladecenter/hardware/chassis/bladeh/specs.html
145 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X O : NE T G E A R FS728TP D A T A S H E E T
The original three page data sheet has been truncated here. The above selection shows
only the part relevant to the project.
If required, the original document can be located at the following URL:
http://www.netgear.com/upload/product/fs728tp/enus_ds_fs728tp_13dec06.pdf
146 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X P : C A T A L Y S T 6 5 0 9 - E P O W E R D R A W I N F O R M A T I O N
The above screen capture shows the contents of an e-mail from IT Services that detail the
power draw information of the Catalyst 6509-E switch. The e-mail address of the sender
is blanked out for privacy reasons.
147 "Power Consumption of Network Devices” Andrew Jess
A P P E N D I X Q : CISCO ASA 558-40 D A T A S H E E T
A selection of the website where the datasheet is displayed is shown above. The above
selection shows only the part relevant to the project.
If required, the original document can be located at the following URL:
http://www.cisco.com/en/US/prod/collateral/vpndevc/ps6032/ps6094/ps6120/product_da
ta_sheet0900aecd802930c5.html