An Introduction to IEEE 802.3az – Energy Efficient Ethernet

By Rajesh K

Energy/ Power conservation in Network devices has got a serious push with the introduction of IEEE 802.3az Standard, also called as Energy Efficient Ethernet. Let us learn more about what is IEEE 802.3az/ Energy Efficient Ethernet and how it can save power, in this article.

Network Device Power Consumption:

While Computers, laptops, Servers, UPS and other IT devices consume a large amount of power, Networking equipments like Switches, Network Interface Cards, etc are not really far behind. It is estimated that networking devices consume about 10% of the total power consumed by IT equipments. With more and more switches/ NIC’s being added to the network, the power requirements for network devices are sure to go up.

One more factor that is contributing to the power increase of network devices is increasing capacity. Switches and Network Interface Cards are transitioning from 100 Mbps to 1000 Mbps and the Network Switches at the Data Center is slowly moving towards 10 GE Connections. Higher capacity always comes with higher power requirements, irrespective of whether the devices are used to their full capacity or not.

These were among many factors that led the IEEE to convene and formulate the 802.3az Standard (Energy Efficient Ethernet). If Network devices (from any vendor) comply to this standard, the power consumption per port would decrease significantly.

Before we look at what IEEE 802.3az is, we need to consider two factors that led to the Standard:

i. Bulk of the active circuitry in network devices remains always on and runs using the maximum power irrespective of whether there is data transmission or not.

ii. Typical Ethernet traffic has occasional bursts at full link capacity, but remains idle for most of the time.

What is IEEE 802.3az/ Energy Efficient Ethernet?

IEEE 802.3az/ Energy Efficient Ethernet is a symmetric protocol that enables network ports to switch between higher power state (data mode) / lower power state (LPI mode) in response to whether data is flowing through them (Active state) / Not (Idle state).

IEEE 802.3az/ Energy Efficient Ethernet uses a technology called LPI – Low Power Idle, which is actually a low energy consumption state that can be used during periods where there is no link utilization.

It should be noted that the IEEE standard defines how LPI is communicated between systems and not why or when it is communicated. Those decisions are left to individual systems.

How does IEEE 802.3az/ Energy Efficient Ethernet (EEE) work?

Each PHY (Network Switch port, NIC, etc) advertises its EEE capability during auto negotiation when a link is established. If the device PHY at both sides of the link support EEE, then they operate in the EEE mode. Even if one of them do not support the EEE standard, they operate in the normal/ legacy mode.

EEE compliant devices use a modified static logic design in order to transcend to the Low Power Idle (LPI) mode when no data is flowing through them.

In EEE compliant devices, LPI (Low Power Idle) signaling protocol is used to convey that a particular link needs to go idle as there is no data transfer during a certain period (which produces a gap in the data stream). But once data flow is initiated through the link, LPI enables the link to resume to its normal operation (Data mode).

When there is no data flow, the link is kept in the sleep mode so that the power consumption (of the device ports that connect from either side) is minimized. But the transmitter sends periodic refresh signals to ensure that the link is functioning and higher level systems (like NMS) can see through them. Of course, the link can be re-awakened at any time. This is especially important in face of unpredictable / latency sensitive traffic.

Advantages of IEEE 802.3az/ Energy Efficient Ethernet (EEE):

* EEE is very effective in reducing the total power consumed per port and it saves a lot of energy on the long run for organizations having a large number of network devices.

* EEE is very effective with edge devices (like computers, edge switches, etc) and can save a lot of power when these devices are EEE compliant as their utilization pattern generally consists of long periods of silence and a few traffic bursts at (almost) full capacity.

* EEE standard does not transition to a lower bandwidth / throughput to achieve power savings. So, 1000 Mbps links remain 1000 Mbps links and does not transition to a lower speed.

* EEE standard operates over standard Base-T interfaces on twisted pair copper wiring and supports 10 Mbps/ 100 Mbps/ 1000 Mbps/ 10 GE.

* EEE is backward compatible with legacy interfaces (that don’t support this standard). Of course, with such interfaces it works normally and does not save power. So, organizations can upgrade their networks gradually.

* The EEE standard gives room for some future improvements (without requiring hardware replacements).

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