Energy Efficient Ethernet

Ethernet link speeds of 100 megabits per second or even 1 Gbit/s per second are typical in today’s LANs. When everything is wired to Ethernet LAN very many LAN connections are needed and they consume some power. And the faster the Ethernet connection is, typically more power it consumes.

IEEE Spectrum Energy-Efficient Ethernet article tells that Ethernet connections waste lots of watts and it need not necessarily need be so. On average, people use their Ethernet links at full throttle less than 5 percent of the time. But the circuitry on the network-interface controller, the chip that connects your computer to the network, is always running at full speed, thus wasting power.

One seemingly simple solution is to adapt the Ethernet link’s speed to match a device’s needs. This concept is called Adaptive Link Rate. The problem in this concept is that switching between Ethernet speeds is time-consuming. When you change link rate today, you have to drop the link and reestablish it, which takes up to 2seconds.

Another concept is called low-power idle, it proposes transferring data on an Ethernet link at the highest possible rate and then putting the network controller chip into a sleep-like state. The trouble is that turning on a dormant network card quickly is a challenge, but it is easier than switching between rates.

Wikipedia Energy Efficient Ethernet article tells that Energy Efficient Ethernet, also known as IEEE 802.3az, is a set of enhancements to the twisted-pair and backplane Ethernet networking standards that allow for less power consumption during periods of low link use. The goal is to reduce power use by 50% or more, while remaining fully compatible with existing equipment. The power reduction is accomplished in a few ways:

• For 100 Mbit/s and gigabit speed links, Ethernet chips that don’t have data to send would put the physical layer of the system into sleep mode. Gigabit interface card might be able to reduce its power by up to 1.5 W.
• For 10 Gbit/s links, speeds are stepped down to slower speeds saving 10 – 20 W per link (twisted pair Gbit/s links consume typically 15W or so power)
• A new lower voltage mode was added to 10Base-T (lower voltage used when full voltage is not needed for example on shorter links)

There were some companies introduced technology to reduce the power required for Ethernet before the standard was set. The best known of them was D-Link’s and Broadcom’s Green Ethernet, which is a superset of the draft 802.3az. Green Ethernet was first employed on home switches and smart switches. D-Link claims that a power savings of up to 45 – 80 percent can be made using its Green Ethernet switches, but I think in real life applications the savings will be somewhat less than those promises.

Broadcom delivers energy-efficient Ethernet silicon article about Broadcom’s portfolio of available silicon supporting the newly ratified IEEE 802.3az-2010 Energy Efficient Ethernet (EEE) standard and proprietary AutoGrEEEn technology. Broadcom Infrastructure & Networking Group, said in a press release, “Energy efficiency is of crucial importance to our customers and to the networking industry as a whole.”

The power savings for an individual consumer level device are likely to be modest compared to the cost of device or the embodied energy, so turning off existing devices when they are idle is likely to be a more immediate savings. If Energy Efficient Ethernet is widely incorporated into new systems, it could reduce networking power requirements as systems are replaced. Green Ethernet Technology is pushing into networking hardware market.