GUEST BLOG: We’ve got EEE. Now what?
ESnet fully supports the drive for energy efficiency to reduce the amount of emissions caused by information and communication technologies (ICT). IEEE just announced that Energy-Efficient Ethernet (EEE) or IEEE P803.3az is the new standard enabling copper interfaces to reduce energy use when the network link is idle . Energy saving mechanisms of EEE can be applied in systems beyond the Ethernet physical interface, e.g. the PCI Express bus. New hardware is required to benefit from EEE, however, so its full impact won’t be realized for a few years. ESnet is in the middle of the Advanced Network Initiative to deploy a cross-country 100G network and we would like to explore end-to-end power saving possibilities including 40G and 100G Ethernet interfaces…Here’s why:
In 2006 articles began to appear discussing the ever-increasing consumption of energy by ICT as well as how data center giants such as Google and Microsoft were locating new data centers based on the availability and cost of energy. Meanwhile, the IEEE was attempting to create a specification to reduce network energy usage, and four years later, ratified the P802.3az or Energy-Efficient Ethernet (EEE).
Earlier this year, the ITU World Summit for an Information Society reported that electricity demand by the ICT sector in industrialized countries is between 5 percent and 10 percent of total demand. But about half the electricity used is wasted by powered on equipment that is idle. So while completion of this project seems timely, the question remains how “triple-e” will impact energy use for Ethernet consumers. EEE defines a protocol to reduce energy usage during periods of low utilization for copper and backplane interfaces up to 10Gb/s. It also reuses a couple of other IEEE protocols to allow uninterrupted communication between link partners. While this combination of protocols can save energy, it is uncertain how much time the typical Ethernet link operates at low utilization, especially when the P802.3ba, or 40G and 100G Ethernet standard was just ratified in June, suggesting relief for pent up demand for bandwidth.
So why isn’t there an energy-efficient version of the higher-speed version of Ethernet?
The answer depends on the type of Ethernet interface and its purpose in the network, as an interface in a home desktop computer will likely be idle much longer than an uplink interface in a data center switch. A key feature of this new standard is called Low Power Idle. As the name suggests, during idle time the non-critical components of the interface go to sleep. The link partner is activated by a wake up signal allowing the receiver time to prepare for an incoming frame.
Consider the utilization plot shown below:
Not all links are the same
This window on a file server in an enterprise network shows plenty of idle periods. While there are several peaks over 500 Mb/s, the server is mostly idle, with average utilization under one percent. On the other hand, there are many examples of highly utilized links as well (just look at some of ESnet’s utilization plots). In those cases, less energy is saved, but the energy is being used to do something useful, like transfer information.
But when considering the number of triple-speed copper Ethernet interfaces deployed, energy savings start to add up. The P802.3az Task Force members estimated power savings in US alone can reach 5 Terawatt-hours per year, or enough energy to power 6 million 100W light bulbs. This translates into a reduction of the ICT carbon footprint by roughly 5 million tons per year.
Since EEE is built into the physical interface, new hardware will be required to take advantage of this feature and it will take a few years to reach 100% market saturation.
Getting back to the question about energy efficiency for 40G and 100G Ethernet, there are a few reasons why LPI was not specified for P802.3ba. This project overlapped with P802.3az so it is difficult to specify an energy-efficient method for the new speeds, given the record size of the project and the lack of P802.3az resources for work on optical interfaces. This leads to another question: Should there be an energy-efficient version of 40G and 100G Ethernet? Or should there be an energy-efficient version of optical and P802.3ba interfaces?
To decide the scope of the project P802.3az we examined the magnitude of power consumed and number of interfaces in the market. The power consumed for a 1000BASE-T interface is less than that used by a10GBASE-T interface, but there are orders of magnitudes more of the former. On the other hand, early in the project not many 10GBASE-T interfaces existed in the market, but the interfaces consumed power on the order of 10W-15W per interface. These numbers are reduced by each new improvement in process technology, but they are still significant.
Considering first generation 100G transceivers can consume more than 20W each and the millions of optical Ethernet interfaces in the market, further standards development is worth pursuing.
Mike Bennett is a senior network engineer for LBLnet and chair of P802.3az. He can be reached at MJBennett@lbl.gov
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