Energy-Efficient Ethernet

Energy-Efficient Ethernet
three green leaves with "e"
Logo of the study group and standard task force

Energy-Efficient Ethernet is a set of enhancements to the twisted-pair and backplane Ethernet family of computer networking standards that will allow for less power consumption during periods of low data activity. The intention was to reduce power consumption by 50% or more, while retaining full compatibility with existing equipment.[1] The Institute of Electrical and Electronics Engineers (IEEE), through the IEEE 802.3az task force developed the standard. The IEEE ratified the final standard in September 2010.[2] Some companies introduced technology to reduce the power required for Ethernet before the standard was ratified, using the name Green Ethernet.


Potential savings

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.[3] According to a researcher at the Lawrence Berkeley Laboratory, Energy-Efficient Ethernet could save an estimated US$450 million a year in energy costs in the U.S.[4] Most of the savings from homes ($200 million), and offices ($170 million), and the remaining $80 million from data centers.[4] The first study group had its call for interest in November 2006, and the official standards task force was authorized in May 2007.[5]


The power reduction is accomplished in a few ways. In 100 Mbit/s, 1 gigabit and 10 Gbit/s speed data links energy is used to keep the physical layer transmitters on all the time. If they could be put into "sleep" mode when no data is being sent that energy could be saved.[4] By sending a low-power-idle (LPI) indication signal for a specified time the transmit chips in the system can be turned off. LPI is sent periodically to refresh the sleep mode. When there is data to transmit a normal idle signal is sent to wake the transmit system up before data is due to be sent. The data link is considered to be always operational, as the receive signal ciruit remains active even when the transmit path is in sleep mode.

In addition, a new lower power mode was added to Ethernet over twisted pair, which reduces power supplies required for each interface.[6]

Green Ethernet

Green Ethernet was a marketing term for Ethernet power-saving technology in 2007 and 2008.

Compared to IEEE Standard 802.3az

Some energy-efficient switch-integrated circuits were developed before the IEEE 802.3az standard was finalized.[7][8]

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 or ‘sleep’ mode when a connected device, such as a computer, is not active. Second, it detects cable length and adjusts the power accordingly. Previous standard switches provide enough power to send a signal up to 100 meters (330 ft).[9] However, this is often unnecessary, especially in the home, where 5 to 10 meters (16 to 33 ft) of cabling are typical between rooms.

Green Ethernet also encompasses the use of more efficient circuitry in Ethernet chips, and the use of "off-load engines" on Ethernet interface cards intended for network servers.[8]


In April 2008, the term was used for switches, and, in July 2008, introduced into wireless routers.[10] A Wireless LAN scheduler using Wireless N Gigabit routers automatically determines when Wi-Fi radio signals are turned on and off to further reduce energy consumption.

Power savings

Green Ethernet was first employed on home products. However, low port counts mean that significant cost savings are not going to be made using this technology only in the home. Turning off existing devices when they are idle is likely to provide a more immediate saving.[11] Projected power savings of up to 45 - 80 percent were estimated using Green Ethernet switches,[12] translating into a longer product life due to reduced heat dissipation.[13]

See also


  1. ^ Sean Michael Kerner (July 17, 2009). "Energy Efficient Ethernet hits standards milestone — InternetNews:The Blog — Sean Michael Kerner". Internetnews blog. Retrieved July 5, 2011. 
  2. ^ "IEEE ratifies new 8023az standard to reduce network energy footprint". October 5, 2010. Retrieved July 5, 2011. 
  3. ^ Prachi Patel-Predd (May 2008). "Energy-Efficient Ethernet". IEEE SpectrumEnergy-Efficient Ethernet: Ethernet connections waste lots of watts. It need not be so ( Retrieved July 5, 2011. 
  4. ^ a b c Rick Merritt (May 8, 2008). "Energy-efficient Ethernet standard gains traction". EE Times. Retrieved July 5, 2011. 
  5. ^ "IEEE 802.3 Energy Efficient Ethernet Study Group". September 21, 2007. Retrieved July 5, 2011. 
  6. ^ "IEEE 802.3az: Energy Efficient Ethernet in the Works". GoodCleanTech blog. Ziff Davis. September 4, 2008. Retrieved July 5, 2011. 
  7. ^ "Top OEMs 'Go Green' With Broadcom's 65nm SMB Switch Family" (Press release). Broadcom Corporation. June 3, 2009. Retrieved July 5, 2011. "'The reduced power consumption offered by these single-chip switch solutions results in an energy saving device with reduced operating costs.' said Jacky Chang, Senior Director at D-Link. 'As part of our D-Link Green™ initiative, we aim to give consumers ecologically friendly choices. By combining Broadcom's switch solutions with our green technology, we have been able to develop our second generation of Green Ethernet switches that provide competitive solutions with enhanced power saving benefits for all of our customers, from home users to enterprise.'" 
  8. ^ a b Nicholas Ilyadis (April 1, 2010). "Broadcom Energy Efficiency Initiatives" (PDF). Broadcom. Retrieved July 5, 2011. 
  9. ^ "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. 
  10. ^ "D-Link First Company to Offer Green Wi-Fi Home Networking". News release (D-Link). July 28, 2008. Retrieved July 5, 2011. 
  11. ^ Tom Higins (April 23, 2008). "How Much Can D-Link's "Green Ethernet" Switch Save You?". Small Net Builder blog. 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. 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. ^ Brad Kenney (April 11, 2008). "Green Ethernet". IndustryWeek. Retrieved July 5, 2011. 

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