Advances in consumer technology and affordable prices have contributed to a substantial presence of home electronics requiring an increasing amount of energy. A common household may contain a digital cable/satellite system, DVD/digital video recorder and gaming console, all complementing a large-screen television. When active, these devices consume hundreds of watts. While these devices can be set to standby, they can consume an average of 440kWh per year. This consumption equates to refrigerators, which consume about 600-700kWh per year. These entertainment setups are not only in European and American homes, but are also found in emerging consumer markets in China and India, whose energy needs are increasing. The prevalence of consumer electronics and rising energy costs have caused government entities worldwide to consider methods to limit device power consumption. Any resulting guidelines or regulation could affect all home electronics, particularly Ethernet-enabled devices. These concerns, along with a growing consumer demand for eco-friendly electronics, have moved equipment suppliers, silicon vendors and even the IEEE 802.3 Ethernet Standards Association to examine ways to make Ethernet energy efficient.

To help minimize consumer electronic energy use, the United States and Europe utilize the Energy Star Program. Energy Star establishes power efficiency benchmarks for electronics such as televisions, video players and computers. However, consumer technology is fast approaching a new milestone, as video is not only viewed by DVD players and cable/satellite systems, but also from high-speed broadband connections allowing users to download video from the Internet. These homes usually connect the devices with a switch or router creating a home Ethernet network (Figure 1). With this type of setup, it is possible to download video to a storage device and view it with a desktop PC or wirelessly with a laptop. The convergence of home data and video systems causes more devices to be simultaneously powered.

Figure 1: A converged home networking

With wireless 802.11n approaching approval and cable modems moving to DOCSIS 3.0, which download data at over 150 Mbps, a simple 10BASE-T system will bottleneck network performance. As a result, the newest routers and switches use 1000BASE-T Ethernet copper physical layer (PHY) ports that can consume 5 to 10 times more power than 10BASE-T.

Examining Figure 1, when the entire family is home after work or school, one person may decide to view streaming Internet videos with a desktop PC, while another uses a laptop to view video downloaded to a local storage appliance. Yet another family member might play a network game with a video game console. The latest switches and routers have enough bandwidth to handle this simultaneous Ethernet network traffic. In the late evening, these devices will go into standby or be powered off. Yet, the Ethernet router will remain active, consuming nearly the same energy regardless of use.

A home wireless router is comprised of a power supply, RJ45 connectors and magnetics, several 1000BASE-T copper Ethernet PHYs, a layer 2 packet switch, a layer 3 routing processor and an 802.11 radio (Figure 2). Examining its overall power consumption, a large percentage of the power is drawn by the 1000BASE-T PHYs running at gigabit speeds, not only when in full use, but also when they are unconnected. A 1000BASE-T PHY generally does not scale in power in proportion to when it is being utilized.

Figure 2: Wireless router device block diagram

IEEE 802.3 specifies Ethernet PHYs. Within this specification, there are no prescribed methods for scaling PHY power based on utilization. One advantage multi-speed copper Ethernet PHYs has is the ability to auto-negotiate between connected PHYs to determine the fastest speed for data transmission. Ethernet Copper PHY auto-negotiation is defined under IEEE 802.3, Clause 28, allowing both PHYs connected via a copper cable to link up as 10BASE-T, 100BASE-T, 1000BASE-T and even the power-hungry 10GBASE-T. Taking power consumption into consideration, when a Clause 28-capable PHY is powered-up and active, it will start the auto-negotiation process trying to connect to a link partner PHY through a twisted-pair copper cable. If a link partner is present, it will establish a link. If there is no link partner, the local PHY will constantly send link pulses trying to auto-negotiate with another PHY. In a situation where the PHY is physically not plugged into a cable, this PHY cannot determine if a link partner is present. It will continue transmitting link pulses, waiting for another PHY to respond. Sending link pulses not seen by another PHY is, in essence, wasting energy.

There are several methods to alleviate the power consumption of an Ethernet switch or router without sacrificing immediate link-up capability and necessary performance. These steps can be implemented through innovation in Ethernet copper PHY technology.

The first step is to enhance the auto-negotiation process already provisioned in copper Ethernet PHYs. Expand on this proven methodology to save power based on the following scenarios (Figure 3): An unplugged PHY port, a PHY port plugged into a cable with no link partner PHY present, or a PHY port plugged into a cable with a link partner PHY who is not transmitting link pulses because it is inactive.

Figure 3: Three scenarios to save PHY power

To save power, the Ethernet PHY can detect the absence of link pulses and subsequently disable both its transmitter and the receiver. The transmitter will no longer be sending link pulses and the receiver cannot interpret and respond to link pulses.

Ethernet can become energy efficient

Global regulation and green-conscious consumers want electronics that operate more efficiently, and have less of an impact on the environment. While several companies have answered the call by delivering products to this eco-friendly segment, more must be done to curb the growing demand in energy consumption by Ethernet-enabled devices.