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Not using all of that GigE pipe? Save some energy

IEEE's Energy Efficient Ethernet looks at ways to throttle down connection speeds to save power

By Phil Hochmuth, Network World
February 02, 2007 09:59 AM ET

Network World - The IEEE wants to make idle or underutilized Ethernet connections more energy efficient, which could mean huge electrical cost savings for large enterprises. The trick: finding a way to seamlessly throttle between 10Mbps and 10Gbps.

The standards outfit recently formed an Energy Efficient Ethernet (EEE) study group to explore how to do this. The idea is to save power in PCs and laptops (most of which ship with GigE cards now) when LAN links are idle, or not utilizing full bandwidth. Researchers estimate that U.S. companies could collectively save $450 million a year in power costs by using such a technology.

The study group is essentially refiguring the process of auto-negotiation — a link-detection technology in Ethernet, where a switch and NIC determine what speeds are supported (10/100/1000Mbps) and establish the link rate. EEE would make this a more real-time process on Ethernet networks. For instance, a GigE-enabled laptop would switch to 10Mbps when idle, maybe 100Mbps during low-bandwidth activities, such as e-mail or Web surfing, and burst to 1000Mbps when downloading large files or streaming video.

"There's lots to take on with this effort," says Mike Bennett, senior network engineer at Lawrence Berkeley National Lab, and chair of the EEE Study Group.

One challenge is finding a way to make a PC or laptop network interface card (NIC) change gears more quickly — "a couple orders of magnitude faster than auto-negotiation, to make the switch as seamless as possible," Bennett says. "Auto-negotiation runs at about 1.4 seconds and we're talking about — just to start the discussion — a millisecond of switching time."

EEE technology will have to work on both ends of a link to be successful, Bennett says. "When one device signals a speed change to another, the device would have to stop transmitting frames and tell the other end of the link, 'Hey, we're going to do a speed change here.'" The challenge with that is there are standard buffering sizes for Ethernet gear, he adds.

"Vendors build devices differently. Some have lots of buffers, some don't," he says.

If the IEEE and equipment vendors can figure all of this out, the savings could be huge for large organizations with thousands of Ethernet ports in PCs, servers and other devices, Bennett says.

Dropping a NIC's connection speed from 1000Mbps to 10Mbps could lower the device's power consumption from about 4W to around .60W. Considering the hundreds or thousands of networked machines running in some enterprises, this power savings could be significant, EEE proponents say.

Presentations given at EEE Study Group meetings cite a 2002 Department of Energy study estimating that the total power consumption of enterprise IT equipment in U.S. offices at around 97 terawatt hours per year, which translates to around $8 billion per year in energy costs. Extrapolating that cost over time, and accounting for network-related power consumption, the study group came up with the estimate of $450 million per year.

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