Green Ethernet

“A free upgrade to the vendor’s IOS operating system being announced today will let some of Cisco’s enterprise routers handle power management. In the most ambitious cases, the router will team up with facilities-maintenance software to turn down lights on the weekends or move office laptops into battery mode.”…Lightreading .com

Cisco just announced its new IOS software that helps to reduce energy “waste” during weekend by fully or partially turning off its router equipments. It is an important movement that Cisco makes since according to some recent research IP routers are the most power-consuming equipments in the telecommunication networks, and power consumption could become a bottleneck for router capacity further upgrade. 

It was said that the software can work in most of Cisco routers, but the greening targets are those low-end routers due to its large numbers, thereby saving more energy, as well as few connected user groups (it is possible to turn them down fully at weekend). It seems not practical to turn down a core router due to its large amount of transit data traffic. Remember we still surf Internet at home at weekend which needs core routers to be on all the time.   

As an alternative greening solution, it is more practical to slow down a core router in its routing speed when traffic intensity becomes low. For example, a regional router may have low data traffic from mid-night to early morning. To realize this, information on the traffic intensity distribution at different time slots is required and the techniques that can automatically turn down and speed up a router speed is also required.

Interestingly, with the annoucement of new router turning down capability, some people raises an important concern regarding security issues. Would the new software capability prvide a new hacking channel for a hacker to fully control a router and even to disable an entire network by maliciously turning off some controlled routers? This security issue should be carefully evaluated before the new software capability is widely upgraded. 

The clock frequency of a chip is related to its energy consumption. The higher frequency is, the more energy will be consumed. In a single-clock chip system, a unique clock is used everywhere for the whole chip, which however may not be energy-efficient because some domain in the chip may actually not require that high frequency. 

To be more energy-efficient, a Multiple Clock Domain (MCD) processor, in which the chip is divided into several (coarse-grained) clock domains, within which independent voltage and frequency scaling can be performed. Based on such architecture, no a unified clock is required for the whole chip, and as a result, energy can be saved for those chip domains that do not need a high frequency. According to some preliminary results reported by a research group from University of Rochester, it is possible to obtain an average energy-delay product improvement of 20% with MCD. Interesting readers may read the following reference:

Energy-Efficient Processor Design Using Multiple Clock Domains with Dynamic Voltage and Frequency Scaling

Research effort and standardization of Green Ethernet have been initialized. One answer that we may be interested in is how much we can save if we adopt the Energy Efficient Ethernet (EEE) technology for global hundreds of millions of NIC interfaces and Ethernet switch interfaces. According to estimation made by a research from Lawrence Berkeley National Laboratory, the energy saving will be large although compared to the energy consumption in other usage such as electronics. The following are some typical values estimated for US energy savings from EEE:

• 1 Gb/s link EEE: $250 to 300 million per year
• 10 Gb/s link EEE: $40 to 80 million per year

See this documentfor the detail. Although such saving is very small compared to the overall electricity consumption of the whole US, we believe that a small step accumulates a large progress!

IEEE 802.3 Energy Efficient Ethernet Study Group was recently formed by IEEE to work on standardization of saving energy on Ethernet technology. The major idea of energy saving is to reduce power consumption based on the link utilization of Ethernet interface.

For example, for an Ethernet interface that can support 10 Gb/s capacity, when the link utilization is high, then the full speed of data transmission will be carried out. However, if the link utilization goes to below 10% of the full speed, then it is possible to switch the interface speed from 10 Gb/s to 1 Gb/s. In general, 1 Gb/s interface speed consumes much lower power than 10 Gb/s interface speed. For an ideal case, it is also possible to change the power level continuously according to the link utilization.

To realize the transition between different types of interface speed and different power levels, protocols and mechanisms should be developed such that the transition will not cause packets dropped and not be noticed by the upper layer protocols and applications. These are just the objectives of the Energy Efficient Ethernet study group.