1. Winter 2011 ESCC/Internet2 Joint Techs
Green Ethernet
Winter 2011 ESCC/Internet2 Joint Techs
Michael J. Bennett
Lawrence Berkeley National Laboratory

2. 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

3. Topics Overview of Energy-Efficient Ethernet (EEE)
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

4. 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 2

5. Rationale
From the Call For Interest presentation

6. Rationale
From the Call For Interest presentation

7. 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

8. 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
PHY
PMA
xxMII – Media Independent Interface
MDI – Medium Dependent Interface
PCS – Physical Coding Sublayer
PMA – Physical Medium Attachement
PHY – Physical Layer Device
AUTO-NEGOTIATION
MEDIUM

9. 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

10. Low Power Idle Overview
Assert LPI
Deassert LPI
Active
Low-Power
Hold
Active
IDLE
Data/
Sleep
Refresh
Refresh
Alert
Wake
IDLE
DATA/
IDLE
Quiet
Quiet
Quiet
Tw_PHY Ts Tq Tr
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: Tw_PHY <= 20.5 usec
1000BASE-T: Tw_PHY <= usec
10GBASE-T: Tw_PHY < usec
Device energy consumption can be reduced by 80%1
1EEE: The new networking protocol for saving watts, datacenterdynamics.com, September 20, 2010

11. 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

12. A system view (switch centric)

13. Opportunities for Innovation
Areas to explore
Improvement of efficiency
How to minimize latency variation
Development of control policies
Integration with Network Management
<your idea goes here …>

14. 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

15. 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

16. 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

17. 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

18. 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?

19. 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

20. Thank You!

21. References
B. Nordman, Digital Networks:
K. Christensen, et.al., "IEEE 802.3az: The Road to Energy Efficient Ethernet," IEEE Communications, November 2010.
W. Diab Use of LLDP,
Dove, Energy Efficient Ethernet: A switching Perspective
P. Reviriego, J.A. Hernandez, D. Larrabeiti, J. A. Maestro, IEEE COMMUNICATIONS LETTERS, VOL. 13, NO. 9, SEPTEMBER 2009
P. Reviriego, et.al., Reduce latency in energy efficient Ethernet switches with early destination lookup,
P802.3az public page,