Green Ethernet
Winter 2011 ESCC/Internet2 Joint Techs
Michael J. Bennett
Lawrence Berkeley National Laboratory
Joint Techs 31 January 2011
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These are my personal views
• Per IEEE-SA Standards Board Operations
Manual, January 2005:
– “At lectures, symposia, seminars, or educational
courses, an individual presenting information on IEEE
standards shall make it clear that his or her views
should be considered the personal views of that
individual rather than the formal position, explanation,
or interpretation of the IEEE.”
• The views expressed in this presentation are
mine and not that of the IEEE
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Topics
• Overview of Energy-Efficient Ethernet (EEE)
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Rationale
What is EEE and where does it fit in the stack?
Low Power Idle
Optimizing Energy Efficiency
Anticipated Benefits
• Opportunities for Innovation
• Possible future development of EEE
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Rationale
• Question about network energy-use began in
2005
– Ethernet traffic is generally bursty
• Sample traffic analysis shows idle roughly 90% of the time
– Interface power on the rise1
• 100BASE-TX ~ 500 mW
• 1000BASE-T ~ 1100 mW
• 10GBASE-T ~ 10,000 mW2
– Could we save energy by reducing energy-use during
idle periods?
1
http://www.ieee802.org/3/az/public/jan08/hays_01_0108.pdf
2 http://www.ieee802.org/3/eee_study/public/mar07/kohl_01_0307.pdf
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Rationale
• From the Call For Interest presentation
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Rationale
• From the Call For Interest presentation
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What is Energy-efficient Ethernet?
• EEE is a method to reduce energy used by an
Ethernet device during periods of low link
utilization
• The premise for EEE is that Ethernet links have
idle time and thus opportunity to save energy
• Specified for copper interfaces
• “BASE-T’s’
• Backplane
• The method we’re using is called Low Power Idle
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Where EEE Fits
OSI Layers
LAN CSMA/CD Layers
APPLICATION
HIGHER LAYERS
PRESENTATION
Logical Link Control (LLC)
SESSION
MAC Control (optional)
TRANSPORT
Media Access Control (MAC)
NETWORK
RECONCILIATION
DATA LINK
xxMII
PHYSICAL
PCS
xxMII – Media Independent Interface
MDI – Medium Dependent Interface
PCS – Physical Coding Sublayer
PMA – Physical Medium Attachement
PHY – Physical Layer Device
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PMA
PHY
AUTO-NEGOTIATION
MEDIUM
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What is Low Power Idle?
• Concept: Transmit data as fast as possible,
return to Low-Power Idle
• Saves energy by cycling between Active and
Low Power Idle
–Power reduced by turning off unused circuits during
LPI
–Energy use scales with bandwidth utilization
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Low Power Idle Overview
Assert LPI
Deassert LPI
Active
Hold
Low-Power
DATA/
IDLE
IDLE
Wake
Tr
Quiet
Alert
Tq
Ts
Quiet
Refresh
Refresh
Sleep
Data/
IDLE
Quiet
Active
Tw_PHY
Tw_sys
Wait a minimum of Tw_Sys before sending data (Tw_sys >= Tw_PHY)
• LPI – PHY powers down during idle periods
• During power-down, maintain coefficients and sync to
allow rapid return to Active state
• Wake times for the respective twisted-pair PHYs:
– 100BASE-TX:
– 1000BASE-T:
– 10GBASE-T:
Tw_PHY <= 20.5 usec
Tw_PHY <= 16.5 usec
Tw_PHY <
8 usec
• Device energy consumption can be reduced by 80%1
1EEE:
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The new networking protocol for saving watts, datacenterdynamics.com, September 20, 2010
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Optimizing Energy Efficiency
• Energy Efficiency can be optimized by using
link-partner communications after the link is
established
– Use Link Layer Discovery Protocol (LLDP) to change
wake times.
– The longer the wake time, the longer the delay till
frames can pass, i.e. latency variation increases
• Trade-off between energy savings and latency
• There are system power savings opportunities in
addition to PHY power
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A system view (switch centric)
http://www.ieee802.org/3/az/public/may08/dove_02_05_08.pdf
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Opportunities for Innovation
• Areas to explore
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Improvement of efficiency
How to minimize latency variation
Development of control policies
Integration with Network Management
<your idea goes here …>
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Opportunities for Innovation
• A couple of examples:
– In October, 2009 Riviergo, et. al. published a paper
examining the energy efficiency of P802.3az (Draft
1.2.1)
– They observed that the wake and sleep times are high
compared to the time it takes to transmit a frame. The
performance was analyzed using a variety of traffic
profiles including traces from data centers
• The analysis suggested there could improvements in
efficiency by buffering and bursting frames
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Opportunities for Innovation
• Further work by Ken Christensen, et. al.
examines the trade-offs in performance of
energy-efficient Ethernet
– Builds from the work described in the previous
paper
– Suggests a packet coalescence mechanism
can be used to further improve energy
efficiency
• This kind of work is essential to the development
of control policies to maximize energy savings
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Possible future developments
• How do we continue the energy-efficiency effort
begun in IEEE802.3az-2010?
– Participation in standards development
• Make sure energy is considered when evaluating possible
new projects
– Encourage EPA to offer incentives network equipment
• Energy Star for network equipment?
– Already working on “Small Network Equipment (SNE)”
– 802.3az referenced as Preliminary Features Under
Consideration in Draft SNE Framework Specification
• Incentives are good for the market
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Possible future developments
• Optical Ethernet
– Optical PHYs were not studied during the
study group phase of the EEE. The following
need to be studied:
• Potential for energy savings
• Whether or not lasers can or should be
cycled off (completely) and on
– Any adverse affects?
• Time to transition between states
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Possible future developments
• There may be opportunities to discover a
better approach to achieving energy
efficiency in new projects
• Impact of other technologies
– How will virtualization/consolidation affect
traffic?
– How will latency-sensitive applications work
with EEE?
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Summary
• Energy-efficient Ethernet will save energy
– At the physical layer
– In the system
• There are trade-offs for saving energy
– Latency variation vs. energy use
• There are opportunities to develop the work done
in P802.3az
– Improvements in efficiency
– Control policy and network management
– Optical and higher speed Ethernet
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Thank You!
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References
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B. Nordman, Digital Networks: http://efficientnetworks.lbl.gov/enet.html
K. Christensen, et.al., "IEEE 802.3az: The Road to Energy Efficient
Ethernet," IEEE Communications, November 2010.
•
W. Diab Use of LLDP,
http://www.ieee802.org/3/az/public/jan09/diab_02_0109.pdf
Dove, Energy Efficient Ethernet: A switching Perspective
http://www.ieee802.org/3/az/public/may08/dove_02_05_08.pdf
P. Reviriego, J.A. Hernandez, D. Larrabeiti, J. A. Maestro, IEEE
COMMUNICATIONS LETTERS, VOL. 13, NO. 9, SEPTEMBER 2009
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P. Reviriego, et.al., Reduce latency in energy efficient Ethernet switches
with early destination lookup,
http://www.embeddedinternetdesign.com/design/224400698
P802.3az public page, http://ieee802.org/3/az/index.html
http://www.energystar.gov/ia/partners/prod_development/new_specs/downl
oads/small_network_equip/SNE_Draft_Framework_V1_0.pdf
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