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Energy-Efficient Ethernet

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three green leaves with "e"
Logo of the study group and standard task force

In computer networking, Energy-Efficient Ethernet (EEE) is a set of enhancements to twisted-pair, twinaxial, backplane, and optical fiber Ethernet physical-layer variants that reduce power consumption during periods of low data activity.[1] The intention is to reduce power consumption by at least half, while retaining full compatibility with existing equipment.[2]

The Institute of Electrical and Electronics Engineers (IEEE), through the IEEE 802.3az task force, developed the standard. The first study group had its call for interest in November 2006, and the official standards task force was authorized in May 2007.[3] The IEEE ratified the final standard in September 2010.[4] Some companies introduced technology to reduce the power required for Ethernet before the standard was ratified, using the name Green Ethernet.

Some energy-efficient switch integrated circuits were developed before the IEEE 802.3az Energy-Efficient Ethernet standard was finalized.[5][6]

Potential savings[edit]

In 2005, all the network interface controllers in the United States (in computers, switches, and routers) used an estimated 5.3 terawatt-hours of electricity.[7] According to a researcher at the Lawrence Berkeley Laboratory, Energy-Efficient Ethernet can potentially save an estimated US$450 million a year in energy costs in the U.S. Most of the savings would come from homes ($200 million) and offices ($170 million), and the remaining $80 million from data centers.[8]


The power reduction is accomplished in a few ways. In Fast Ethernet and faster links, constant and significant energy is used by the physical layer as transmitters are active regardless of whether data is being sent. If they could be put into sleep mode when no data is being sent, that energy could be saved.[8] When the controlling software or firmware decides that no data needs to be sent, it can issue a low-power idle (LPI) request to the Ethernet controller physical layer PHY. The PHY will then send LPI symbols for a specified time onto the link, and then disable its transmitter. Refresh signals are sent periodically to maintain link signaling integrity. When there is data to transmit, a normal IDLE signal is sent for a predetermined period of time. The data link is considered to be always operational, as the receive signal circuit remains active even when the transmit path is in sleep mode.[9]

Green Ethernet[edit]

Green Ethernet technology was a superset of the 802.3az standard. In addition to the link load power savings of Energy-Efficient Ethernet, Green Ethernet works in one of two ways. First, it detects link status, allowing each port on the switch to power down into a standby mode when a connected device, such as a computer, is not active. Second, it detects cable length and adjusts the power used for transmission accordingly. Standard switches provide enough power to send a signal up to 100 meters (330 ft).[10] However, this is often unnecessary in the SOHO environment, where 5 to 10 meters (16 to 33 ft) of cabling are typical between rooms. Moreover, small data centers can also benefit from this approach since the majority of cabling is confined to a single room with a few meters of cabling among servers and switches. In addition to the pure power saving benefits of Green Ethernet, backing off the transmit power on shorter cable runs reduces alien crosstalk, and improves the overall performance of the cabling system.

Green Ethernet also encompasses the use of more efficient circuitry in Ethernet chips, and the use of offload engines on Ethernet interface cards intended for network servers.[6] In April 2008, the term was used for switches, and, in July 2008, used with wireless routers which featured user-selectable off periods for Wi-Fi to further reduce energy consumption.[11]

Projected power savings of up to 80 percent were predicted using Green Ethernet switches,[12] translating into a longer product life due to reduced heat dissipation.[13]

See also[edit]


  1. ^ IEEE 802.3 Clause 78
  2. ^ Sean Michael Kerner (July 17, 2009). "Energy Efficient Ethernet hits standards milestone — InternetNews:The Blog — Sean Michael Kerner". Internetnews blog. Archived from the original on July 18, 2009. Retrieved July 5, 2011.
  3. ^ "IEEE 802.3 Energy Efficient Ethernet Study Group". September 21, 2007. Retrieved July 5, 2011.
  4. ^ "IEEE ratifies new 8023az standard to reduce network energy footprint". Lightwaveonline.com. October 5, 2010. Archived from the original on October 9, 2011. Retrieved July 5, 2011.
  5. ^ "Top OEMs 'Go Green' With Broadcom's 65nm SMB Switch Family" (Press release). Broadcom Corporation. June 3, 2009. Retrieved July 5, 2011.
  6. ^ a b Nicholas Ilyadis (April 1, 2010). "Broadcom Energy Efficiency Initiatives" (PDF). Broadcom. Archived from the original (PDF) on June 13, 2010. Retrieved July 5, 2011.
  7. ^ Prachi Patel-Predd (May 2008). "Energy-Efficient Ethernet". IEEE SpectrumEnergy-Efficient Ethernet: Ethernet connections waste lots of watts. It need not be so. Spectrum.ieee.org. Retrieved July 5, 2011.
  8. ^ a b Merritt, Rick (May 8, 2008). "Energy-efficient Ethernet standard gains traction". EE Times. Retrieved July 5, 2011.
  9. ^ Spurgeon, Charles (2014). Ethernet: The Definitive Guide. O'Reilly. pp. 119–120. ISBN 978-1449361846.
  10. ^ "Ethernet 100BaseTX and 10BaseT Cables: Guidelines and specifications". Cisco 10000 Series Routers. Cisco Systems. August 1, 2006. Specifications and Connection Limits for 100-Mbps Transmission. Retrieved August 29, 2010.
  11. ^ "D-Link First Company to Offer Green Wi-Fi Home Networking". DLinkGreen.com. D-Link. July 28, 2008. Archived from the original on March 3, 2016. Retrieved July 5, 2011.
  12. ^ "D-Link First Company to Offer 'Green Ethernet™' Technology for Network Connectivity, Embrace Energy-Saving Initiatives". D-Link. October 24, 2007. Archived from the original on March 3, 2016. Retrieved July 5, 2011. For example, when connected and subsequently powered down, the DGS-2208 multi-port desktop switch can realize up to 80 percent savings in power usage*, and the other D-Link 'Green Ethernet' switches can save up to 45 percent in power usage.
  13. ^ Kenney, Brad (April 11, 2008). "Green Ethernet". IndustryWeek. Archived from the original on 2013-06-02. Retrieved July 5, 2011.

External links[edit]