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Title: 802.3az  
Author: World Heritage Encyclopedia
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Subject: IEEE 802.3
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Energy-Efficient Ethernet is a set of enhancements to the twisted-pair and backplane Ethernet family of computer networking standards that 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 first study group had its call for interest in November 2006, and the official standards task force was authorized in May 2007.[2] The IEEE ratified the final standard in September 2010.[3] 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.[4] 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 from homes ($200 million), and offices ($170 million), and the remaining $80 million from data centers.[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.[5] 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 circuit remains active even when the transmit path is in sleep mode.


Features compared to Green Ethernet

Some energy-efficient switch-integrated circuits were developed before the IEEE 802.3az standard was finalized.[6][7]

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).[8] 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.[7]


In April 2008, the term was used for switches, and, in July 2008, introduced into wireless routers.[9] 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.[10] Projected power savings of up to 45 - 80 percent were estimated using Green Ethernet switches,[11] translating into a longer product life due to reduced heat dissipation.[12]

See also


External links

  • IEEE P802.3az Energy Efficient Ethernet Task Force
  • Blog for Energy-Efficient Ethernet techniques and news analyses, circa 2009.

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