Networking

A greener choice

Computing and network hardware has traditionally been benchmarked on performance with no clear metrics for energy efficiency. And because the focus of development has been ever-higher performance, there has been a rapid increase in power consumption, particularly since the advent of multi-GHz processors. The EPA reports that energy usage in data centres doubled between 2000 and 2006 and is predicted to double again by 2011.

Data centres are built to handle peak loads and often have excess capacity off peak. It's nice to have a lot of server cores available to tackle a big problem when you need them, but it costs a lot of money for power and cooling to keep those servers running constantly.

Clearly there are efficiencies to be gained by being able to operate the compute infrastructure in a manner that scales the power consumption down when the load is lower. Consider, for example, a data centre built to provide stock quotes within seconds — the servers are woefully underutilized when the market is closed. Making the power consumption proportional to the load would allow close to a ten-fold reduction in power consumption as the average utilization tends to be less than 10% of peak capacity.

This is where IEEE 802.3az, or the Energy-Efficient Ethernet (EEE) standard steps in, which aims to reduce the power consumed by Ethernet equipment. Expected to be finalised next year, this new standard will implement low-power idle (LPI) modes for the full range of Ethernet BASE-T transceivers (100Mb, 1GbE and 10GbE) and the backplane physical layer standards (1GbE, 4-lane 1GbE and 10GbE).

When the energy efficiency standards activity started in the 802.3 working group, one of the options considered was stepping down the power consumption of Ethernet transceivers (PHYs) in stages when the data rate required was less than peak. That idea was abandoned, after much debate, in favour of defining LPI modes and mechanisms to switch rapidly between the full operating speed and the low-power idle mode.

With this approach, the EEE standard will not only be able to improve the efficiency of data centre network equipment, but also provide standardised signalling mechanisms that can enable rapid transitions between normal operation and LPI states in systems on either end of the physical layer link.

This capability is reminiscent of the Wake-on-LAN standard (which defines magic packets that can be sent to remotely wake up a computer in a sleep mode), however, EEE signalling has much less latency, on the order of 10 microseconds.

How to get there

What steps should IT organisations take now to be ready for Energy Efficient Ethernet? One of the best things an IT organization can do to prepare is to get a good overview of the technology and understand how it will tie in other energy-conscious standards, such as the Energy Star programs. Companies can save considerable cost if they plan ahead and prepare rollout plans for device replacement and upgrades so that they can incrementally introduce devices that support the technology.

The full potential of Energy Efficient Ethernet can only be achieved once the network equipment as well as the networked servers and desktop equipment support the protocol. When we consider that the normal lifetime of networking gear vs. the lifetime of servers is typically different it’s easy to imagine that it will be difficult to match the buying cycles of the two. Fortunately the EEE interfaces are designed to be backwards compatible which means that one could have an EEE interface connected to a normal Ethernet interface. This won’t achieve energy savings but it allows a phased approach to the introduction of the technology into the network,” says Paulo Periera, Systems Engineering Manager, Cisco.

The IT organisation should take a stepped approach and use the coming buying cycles of either networking equipment or servers/desktops to introduce the technology keeping in mind that in order to achieve interoperability in the future it is important that the implementations adhere to the standard and not to a pre-standard or draft version of the EEE standard, he adds.

Gautam Raj, Sales Manager, HP Networking, says an organisation should be looking for Miercom certified products and should take a real interest in the power consumption of their networking devices. “When we refer to Energy consumption of devices, it is more than just the power consumed by these devices. The more the power consumed by the devices, the more heat they generate. The more heat they generate, the cooling requirements go up.”

Will supporting it require forklift upgrades or will it more generally involve swapping out cards or software on existing gear? In other words, will there be a big up- front cost? Experts say the 802.3az standard only covers the physical layer of the OSI stack and therefore will only involve swapping out adapter cards and switching hardware at first. However, as future standards begin to reference this standard, more complex software and hardware options may become available.

“This depends mainly on the possibilities offered by the supplier. Using more energy efficient gear normally requires a forklift upgrade; however, there may be some software features that vendors will bring to the market to reduce power, when certain functions are not needed. An example of this is switching-off the Power over Ethernet on a port when the device connected to that port is not used. But it will be very vendor specific as to whether this additional functionality can be delivered on existing switches, if it will require an additional software license, and if can be done fully automatically or only manually,” says Aziz Ala’ali, Regional Director, Extreme Networks.

Pereira of Cisco adds that EEE involves changes to the physical layer of the Ethernet Protocol and therefore will require new Ethernet controllers with support for EEE. “However, because EEE is backward compatible with Ethernet, the technology can be introduced gradually without the need for any forklift upgrades.”

Adopting Energy Efficient Ethernet is expected to bring in enormous power savings for oraganisations. Though it will depend on network usage, when in the low power stare PHYs will save somewhere in the vicinity of 80% of the energy they would use in a fully powered state.

The real power savings that are made possible through 802.3az will be when higher layer standardization efforts begin to leverage that these PHYs have entered a low power mode and begin to turn off additional system level parts. There are already efforts in standards like Energy Star to include EEE as part of the overall system of power saving capabilities.

“The total power savings of EEE will come from both sides of an Ethernet connection, the server and the switch. On smaller switches, the physical layer can consume up to 40% of the total switch energy consumption and the introduction of EEE is estimated to provide savings of up to 80% on that layer. It will take multiple generations before the power savings ripple into the rest of the system, but we estimate that total power savings greater than 60% should be feasible in 4-8 years,” says Pereira.

Energy Efficient Ethernet is often confused with Power over Ethernet. From a technical standpoint, there is no connection between both these Ethernet technologies. However, they are both aimed at reducing overall power usage. Where EEE is focused on saving power during periods of low utilisation in a single system, Power over Ethernet is focused on actually providing power to small devices that have Ethernet connections in a distributed manner to reduce the number of AC/DC conversion points.

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