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31 January 2011 
HP has announced the first Ethernet switch modules that make use of the IEEE 802.3az Energy Efficient Ethernet (EEE) standard. The standard, ratified in October 2010, is designed to save power by putting the Ethernet physical layer (PHY) to sleep when the network is idle.  Several vendors including Broadcom and Vitesse Semiconductor have chips that support the standard.


HP’s latest E-Series zl modules include a range of 10 Gigabit and Gigabit Ethernet adapter cards that fit into its HP 8200 and 5400 switches. Independent test lab, The Tolly Group, assessed the switches with the latest EEE-compliant cards against Cisco Systems’ Catalyst 3750-X and 4500 switches that do not have EEE. The HP switches consumed 2.1 to 2.3 Watts per Gigabit-per-second (W/Gbps) whereas the two Cisco switches consumed 8 and 20.8W/Gbps.

Traditionally, Ethernet frames are sent across a link even when the network is idle. Now with EEE, the copper transceivers are turned off when there is no traffic while periodically refresh signals are sent to maintain synchronisation between the two ends. The EEE standard allows for parameters to be shared between the end devices to determine how long the drivers are in the off state, the refresh burst duration as well as how the link is brought back from the low-power idle mode to its active state.

Moreover, the EEE standard allows for higher-level control mechanisms once the link is established. For example the sending end can wait for 10 packets to arrive before turning on the link rather than the less power-efficient sending of each packet as it arrives unless, of course, the particular packet is a high priority one and cannot be delayed due to latency issues. 

Several chip vendors have silicon supporting the IEEE standard. Vitesse says all its products introduced in 2010 are EEE compliant. These include the SparX-III switching products and the VSC8512 and the VSC8522 PHYs.  Broadcom has implemented EEE as part of its 10/100/1000BASE-T and 10GBASE-T PHYs, 1 and 10 Gigabit Ethernet controllers as well as its switches. Broadcom’s EEE PHYs are being used as part of HP’s E-Series zl modules.

There is also discussion in the industry about developing a green scheme for optical-based Ethernet links with announcements likely in the coming months, according to Vitesse.
by Roy Rubenstein.