A leading wireless analyst has vindicated Siemens' surprising claims to have cracked an 802.11n problem which has stumped other Wi-Fi vendors. But how Siemens achieved its feat remains secret.
All other enterprise Wi-Fi vendors, including Cisco, Aruba and Trapeze, maintained that the new standard – running at full power, with two radios each of which can deliver multiple streams of data – will take more electrical power than industry-standard power-over-Ethernet can deliver.
This is critical in offices, where access points are powered over Ethernet, because pulling new power cables is expensive. So most Wi-Fi vendors have offered different workarounds that either reduce performance or boost the power on the cable.
Siemens challenged this with HiPath access points announced in January, that it says can give full 802.11n wireless performance without exceeding the power limits of IEEE 802.3af power-over-Ethernet, but declined to explain how.
Now independent analyst Craig Mathias of the Farpoint Group has verified the claim, although he still had no explanation.
Mathias took a HiPath AP3620 802.11n access point and powered it from various industry standard switches and injectors. Two laptops were linked by wireless to the access point, each of which could generate up to four streams of traffic, verifying that multiple streams of data were being carried, using MIMO (multiple input multiple output).
"We saw outstanding performance," said Mathias. Both radios were delivering high throughput consistent with 3x3 MIMO (three antennas in use at both client and access point). Mathias used a full 100m of Cat 5E cable to connect the AP, and used +20dB pads on the antennas to compensate for the fact that the laptops were within a Faraday cage about a metre from the AP.
"While we were sceptical of Siemens' claim that 802.3af power would be sufficient for dual-radio, 3x3 MIMO operation, they have clearly achieved this feat," said Mathias in his report. "Enquiries to their engineering staff as to how they managed this were met with polite smiles.
"We expect Siemens to gain some real market advantage from this for some time," says Mathias. The achievement could allow Siemens' installations to be cheaper, or give higher performance than others.
Cisco requires a proprietary power injector for full 802.11n performance. Trapeze suggests using two Ethernet cables for power. Aruba suggests that the full performance might work, but offers the chance to fall back on less than 3x3 MIMO.
The HiPath Wireless AP3620 has also just received a certificate form the Wi-Fi Alliance for complying with the 802.11n draft standard.
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