FOCUS NETWORKING UPDATE
Issue 12, Oct/Nov
FOCUS UPDATE: NETWORKING
energy in the physical layer (PHY) of Ethernet networks. The PHYs selected for work in this project include the popular 100BASE-TX and 1000BASE-T PHYs, as well as emerging 10GBASE-T technology and backplane interfaces, such as 10GBASE-KR. The method of power savings currently planned for these PHYs is a technique known as low-power idle (LPI). In the low-power state, PHYs will save somewhere in the vicinity of 80% of the energy they would use in a fully powered state.
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WIRING CLOSET APPLICATIONS Figure 1 shows a traditional enterprise wiring closet application. A switch can be connected directly to computing clients, voice-over-IP (VoIP) devices and/or WLAN access points.
The sheer number of links in this application makes for attractive savings. As the horizontal links have steadily moved from 10M to 100M and are now dominated by gigabit, the uplinks have moved from gigabit to 10 gigabit and faster. This type of application also has a very natural opportunity for time-of-day savings, when the network is naturally at a low-usage level.
TOR APPLICATIONS Figure 2 shows the configuration used by a growing segment of data centers with a top-of-rack (TOR) switch connected to a pool of servers. Such setups are becoming increasingly popular in many areas, such as service provider, content provider and enterprise cores.
GREEN NETWORKING To understand the innovation possible at the system level by building on top of the standard, it is important to introduce a simple but powerful framework showing how energy is consumed and how savings happen:
ET = [Pactive * Tactive] + [Pidle * Tidle]; where T = Tactive + Tidle
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www.datacenterdynamics.com EEE Enabled Server Controller TOR configuration FIGURE 2
he Institute of Energy Efficient’s (IEEE’s) EEE P802.3az standard, also known as energy efficient Ethernet (EEE), is targeted at saving
TRIPLE Es OF NETWORKING IEEE senior member Wael William Diab examines traditional versus next-generation networks. He explains how and why EEE will be adopted
ENERGY EFFICIENT ETHERNET – THE
EEE enabled GigE or 10G links (for<meter links)
EEE, one has to think of what EEE provides. Unlike a standalone system, networking systems communicate with their link partners.
EEE enabled GigE links
FIGURE 1 Traditional enterprise wiring closet app
ET represents the amount of energy consumed over a period of time, represented by T. Think of your monthly energy bill. This would proxy the meter reading month over that month, with T being a month and P being power consumption. The higher E is over a period of time, and the more energy is consumed the higher the bill (cost in $, for example). To maximize the savings, this equation needs to be minimized.
Assume that a networking device has two states – active and idle. The total energy consumed would be the energy used while the device is in that active state, added to the energy consumed when it is in the idle state.
Going back to fundamentals, the energy in any state can be described as the product of the average power consumption in that state by the time spent in the state. To maximize the power savings, we look to three areas: minimize pactive, minimize Pidle and maximize Tidle. To tie back the equation to
Data Center Rack
EEE enabled GigE or 10G links (for<100meter links)
Similarly, performance and features of the PHY beyond the bit error rate (BER) specification in the IEEE Std 802.3-2008 is also implementation specific.
EEE enabled 1 and 10GBASE-T links
2. Power optimization in subsystems above the physical layer – EEE not only enables direct energy savings, it enables additional subsystems to be powered down. This concept relies on the fact that a higher layer subsystem can also ‘go to sleep’ when it knows the
Pactive is the power consumption of the system and its devices without EEE being active. This is the traditional Ethernet power consumption discussed earlier. Innovations in this area are especially exciting and include:
• Lower energy process nodes; • Clock frequency management on client devices;
• Energy efficient memories; • Scaling power consumption based on cable length (auto green mode);
• Turning off an unused port (auto power- down mode); and
• Turning off on-chip memory banks in certain configurations.
Pidle is the system’s power consumption in the idle state. It can be split into two categories:
1. Power consumption of the EEE- compliant subsystems – Perhaps the most obvious component of the savings equation, this portion covers the consumption and efficiency of the physical layer device complaint to EEE.
It is noteworthy to mention that the IEEE P802.3az does not specify or guarantee a level of consumption. The EEE amendment to the IEEE Std 802.3-2008 simply creates a lower energy state and allows for interoperability between link partners. The actual consumption of the subsystem is dependent on architecture and implementation.
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