Can you really do full-speed 802.11n using standard power-over-Ethernet? Yes, you can...

Siemens claimed earlier this year that its access points can deliver dual-radio 802.11n Wi-Fi using power standard 802.3af power over Ethernet (PoE) - the normal way to power enterprise access points.

Finally, assisted by an OEM partner, tests have shown they actually do just that.

Analyst Craig Mathias, of Farpoint Group did some tests in March that showed the Siemens AP worked, in full 802.11n dual-radio mode, powered by a range of standard PoE supplies. But the test didn't measure the actual power delivered - leaving the nagging possibility that maybe the supplies were being over-generous with the wattage.

Mathias isn't one to leave a gap like that, so he's tested the same kit again - albeit under a different badge - this time measuring the power consumption.

Extreme Networks started selling the Siemens APs in April, and announced greener switches at the same time, designed to help network managers cut power consumption. Mathias used a power monitor built into one of these switches to measure the actual power drawn by an 802.11n access point - this time a Siemens AP with an Extreme badge on it - connected over 100m of Cat5 cable. He also had a Psiber LanMaster Ethernet analyser to measure the power.

It turns out the AP uses less than 12.2W at all times. That's comfortably under the 12.95W guaranteed by 802.3af - especially when you consider this was the figure measured at source, by the switch, so it includes any power lost in the cable as well. And just to show Craig knows what he's doing, here's some circumstantial detail: the access points used most power when sending information to the laptop. When the Iperf test script was receiving data from the client, the power consumption went down to 8W. That's because a radio takes less energy receiving signals than it does sending them.

The result is interesting because, before Siemens made its announcement, other vendors had claimed that dual-band 802.11n needed more power than 802.3af could deliver. To my knowledge, no one else has shown this ability, and Craig has removed most of the doubts raised in comments to his original post on the subject.

We hear that Bluesocket and Meru have claimed to run on 802.3af - perhaps we'll hear more.