Getting green power over Ethernet
Daniel Feldman explains his view of the energy-saving advantages of Power over Ethernet (PoE)
Feldman: Deploying PoE can save energy
The biggest Power over Ethernet (PoE) savings, in my opinion, would come from equipment that can be programmed for pre-determined shut-down periods. I believe this kind of kit can reduce power consumption by as much as 70 per cent.
PoE enables power and data to be delivered simultaneously over CAT5e or better cabling. You no longer need electrical outlets in hard-to-reach locations, and have network-enabled energy management options.
The latest PoE technology should comply with the IEEE’s 802.3at-2009 standard, going beyond supporting low-power devices such as IP phones and WLAN access points to support high-definition (HD) network cameras, 802.11n access points and thin clients as well. Either a PoE-enabled switch or a midspan system is inserted between a non-PoE switch and the devices to be powered.
PoE helps you centralise power back-up in applications such as IP telephony that require 99.999 per cent availability. It simplifies electrical infrastructure deployments because it is a Separated Extra Low Voltage (SELV) technology (<60V) and handles detection and classification at voltages below 30V.
This means you do not need an electrician to do the deploying.
PoE may also enable remote management for maintenance re-sets and scheduled shutdowns. Devices such as IP phones, for example, can be set up to operate only during working hours, potentially saving energy.
The 802.3at-2009 specification means up to 51W of power can be delivered to powered devices, or 25.5W can be delivered with half the power dissipation and 15 per cent lower energy consumption than conventional 2-pair solutions. Device detection, classification, disconnection and protection from overload or short conditions, and smart energy-management features, are included.
Until now, there has been no way to encourage the use of PoE offerings. A certification programme, which addresses the challenges faced by a PoE switch industry, where there has been no unbiased way to test PoE switch efficiency, might work best.
Ethernet-switch efficiency testing relates only to the power consumed when sending data packets, with no PoE loads. This is meaningless for PoE switches, for which approximately 90 per cent of the power is used to feed electricity to devices, and 10 per cent is used to power the data-switching components.
You can measure the ratio of DC out/AC in full-power and half-power load for the complete switch. This method also allows for the testing of midspans, which are an increasingly important platform for deploying PoE.
The criteria for greenness should also be straightforward. For example, the top 25 per cent of switches in terms of efficiency are green; the others are not.
I believe utilities will like the idea of giving incentives to IT managers who know they can save money deploying a green PoE switch or midspan.
In the US’s Smart Grid, PoE will make it possible for low-priority users to be shut down in case of demand peaks. Offerings can also be developed that integrate Smart Grid controls and PoE controls. This would potentially allow utilities to instruct users to shut down their lowest-priority PoE devices to save power, rather than doing a complete shut-down.
This will help systems do better in times of catastrophe, or in demanding environments. Energy utilities should incentivise customers to save power.
Daniel Feldman is director of marketing in the telecoms analogue mixed-signal group at Microsemi