Energy saving has so far focused on PCs, servers and the like, but now networks have been fingered as major wasters of power. An industry group has claimed that Ethernet's poor use of energy could be wasting as much as $450m a year - or 5.8TW-h - in the US. And perhaps three times that much, worldwide.
The figures come from the Energy-Efficient Ethernet (EEE) Study Group, a new body backed by the IEEE and the Ethernet Alliance, which is charged with developing technologies and specs for Ethernet power management.
A lot of the problem is connections running at higher speeds than they need to, said EEE chair Mike Bennett. He added that the problem has worsened as more and more systems - from business servers and network printers to home IPTV set-top boxes - are left on 24x7.
"For example, measured at the wall socket, a device that operates at 100BASE-TX instead of 1000BASE-T when the link is operating well under 100Mbit/s could save close to 2W," he said. "Multiply that by two for the other end of the circuit and you're saving roughly 4W per link. It may not sound like much, but over an enterprise with thousands of links, it can add up."
He added that power wastage is going to get worse as Gig and 10Gig Ethernet use ramps up. Early 10Gig server NICs burn as much as 24W, but Bennett pointed out that most are also multi-speed and can auto-negotiate, so there is the opportunity to cut power use by cutting the connection speed when it's not under load.
"The key to all this is how much can be saved (ie. not wasted) with technology presently on the market, and how much could be saved by easily imaginable but not yet available technology," he said.
"We're going to look at ways to reduce power consumption by switching to lower speeds during periods of low link-utilisation."
One challenge will be speeding up Ethernet auto-negotiation so it can toggle between low and high speed quickly enough to handle bursty traffic.
Several other organisations backed the EEE, including some that have already done work on energy efficiency that could feed into the EEE's specs.
"The ability to change speeds for power reduction is already present in the EU code of conduct on broadband equipment for DSL," said Paolo Bertoldi, a researcher with the European Commission. "Extending this to Ethernet is a logical and important next step."
"We are interested in both the direct use of energy from networking, and how being networked induces higher energy use in products," added Bruce Nordman of the US Lawrence Berkeley National Laboratory.
Nordman acknowledged that while 5.8TW-h sounds a lot, it is less than one per cent of total US electricity use. But as you reduce energy use to manageable problems, most of these end up being under one per cent, "so that fact is not especially relevant to whether it is worth doing".
He continued: "The fact that network energy usage seems to be rising doesn't mean that what we do to reduce the rate of rise isn't worth it.
"We need to also look at the whole system - edge devices, NIC energy (in edge and network devices), and the energy in the rest of the network equipment, and optimise all of it." ®