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Faster, Cheaper, Cooler: Energy-Efficient Ethernet on the Horizon
by Lee H Goldberg
Back in the days when 10BASE-T Ethernet was considered to be screaming-fast, gasoline was not much more than a buck-a-gallon and electricity was a few cents per kW-hr. Even when 100BASE-T came on the scene in the early nineties, energy was relatively cheap so nobody really gave much thought about how much power it took to shove a bit across a network. But somewhere around the turn of this new century considerable thermal issues involved with early Gigabit Ethernet technologies aroused the interest of technologists and the seeds for the 802.3az Energy-Efficient Ethernet were planted A recent conversation with Solarflare Communication CTO George Zimmerman provided a good overview on the current status of Energy-Efficient Ethernet (EEE) technologies and standards.
When I talked with Zimmerman a couple of weeks ago, he said that the 802.3az task force was still in the process of defining its requirements but he was hopeful that their Draft 1.0 document should emerge by early October of this year, a milestone that would keep the final standard on target for ratification in early 2010. Although the 802.3az standard is still a moving target, several important decisions have already been made that will determine much about how the final standard works and the features it supports The original rate fallback scheme that would allow Ethernet transceivers to re-negotiate their data rates on the fly has been shelved. In its place, Intel’s low-power idle scheme (with a keep-alive heartbeat to maintain connection) has been adopted for further development and will be applied to most PHYs (except 10BASE-T which has a separate spec that lowers its signaling voltage).
Instead of constantly passing null bytes when there is no data to send, the low-power idle scheme puts the transceiver into a keep-alive mode that passes just enough traffic to keep equalizer settings, CDRs, and canceller settings active and accurate. Current studies indicate that a properly-designed transceiver can spend 95% of its time in a low-power state and still be ready to send or receive data but the specific duty cycle to be used by the 802.3az standard is still being debated in committee at the time of this writing. Assuming that the idle duty cycle finally defined by the 802.3az committee is somewhere around 5%, it will shave 85% off the 4/6 W operating power of a typical 10G PHY during idle. About the only drawback to this approach is that both sides of a connection must be EEE-capable to support the power-saving idle mode, although an 802.3az-compliant transceiver is backward-compatible with older silicon.
The 802.3az standard will do much more than slash the operating power of Ethernet PHY layers. Smart designers will be able to take advantage of the PHY low-power idle mode to dramatically reduce overall power consumption throughout their networking equipment. Once a switch, router or server detects an idle packet, it will have the option of turning its buffer RAM off, turning down its MAC interfaces, slowing down its control processors, and turning off any other system elements that can be turned back on within the 10 µs window that the 802.3az specification allows for wake-up when normal traffic resumes. Zimmerman estimates that networking equipment could shave as much as 80% off an idling system power budget if all elements are designed to use EEE mode.
If you are one of the folks at your company who will be developing the next generation of networking equipment, it’s probably a good idea to follow developments in the 802.3az standard as they occur by checking in at the standard committee’s web site from time to time. For more news on analysis, you can also visit George Zimmerman’s Up and Down the Network Stack blog which usually has lots of juicy EEE-related tidbits.
It’s going to be some time before the 802.3az spec is finally firmed up (current estimates place final ratification in spring of 2010) but it’s important to start thinking about how it’s going to affect your design practices. Since most 10GbE chip makers are busy developing EEE-compliant silicon in parallel with the standard it’s likely we’ll see pre-standards alpha devices in preferred customer hands in late 2009/early 2010 with the first fully 802.3az-compliant devices emerging 3 - 6 months after the standard is finalized. In the interim, energy-conscious designers can take advantage of some of the ad-hoc interim solutions that are already in common use. Most of the PHY layer initiatives that manufacturers use to power-down unused ports and wait for an auto-negotiation or wake-on-LAN signal don’t require standards and can be implemented immediately.
The potential energy savings made possible by 802.3az and related technologies could make a small but real difference in our struggle with global climate change. It can also help your customers dramatically cut their energy and cooling costs. In both cases, Energy-Efficient Ethernet will quickly become a must-have feature for almost any product sporting an Ethernet connection.
Comments? Questions? Speculations about what Sarah Palin was wearing in her ear during the vice-presidential debate? Write me at lhg at en-genius dot net or post your comments on our blog.
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