• 03/09/2008
    3:46 AM
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Siemens' PoE Claims Validated

Farpoint Group validates Siemens' claims that it can power a 802.11n AP draft 2.0 access point with standard 802.3af.
At first blush it would seem as though the enterprise Wi-Fi vendor community has become a trend-follower and gone green, focused on saving power at every turn. But the potential power demands of dual-radio 802.11n Draft 2.0 access points have sent engineers back to the drawing board. The current PoE (Power over Ethernet) standard, IEEE 803.af, only delivers 12.95 W at the end of a 100-meter Cat5E cable, but without optimization, power consumption can easily be in the upper teens. Siemens, not unlike other enterprise WLAN vendors, knows that requiring customers to install new and proprietary separate PoE injectors or midspan adapters until the new PoE standard, IEEE 802.3at, was ratified and had shipping product, wasn't an ideal approach for the launch of its 802.11n product line. Although Siemens hasn't shared specific details, it claims to have done some tweaking on the board design and components that allows it to deliver 3x3:2 (three transmit and three receive antennas, with two spatial streams) using a 40-MHz wide carrier at full power, without compromise, on existing 802.3af installations. Since most enterprise Wi-Fi vendors have chosen Atheros for their Wi-Fi chipset, there's little tweaking that can be done on the most significant power consuming component, though Atheros will continue to improve the efficiency of its chipsets.

Some competitors dismissed Siemens' claims when their product was announced several weeks ago, perhaps because they saw it as an impossible achievement or, in their own attempts, weren't able to match it. A quick overview of existing product in the market is helpful. First out, Meru, has taken a very pragmatic but most up-front approach: You need to use a pre-802.3at injector or midspan device, or use a power supply. Next up, Cisco also admitted to exceed 802.3af limits, but points to certain series of its switches and some blades, which can provide a little extra power, something I like to call "PoE boost." If a customer doesn't have those switches or blades, they can fall back to the same thing Meru proposes. When Aruba initially announced its product, it claimed 803.3af support with full capabilities for most cable runs, but has modified the messaging and expanded that to all cable runs that meet standard specifications and lengths.

Siemens' claims, dramatic as they are, could stand to be evaluated by an independent third party, and so Siemens asked Craig Mathias, a wireless consultant and principal at Farpoint Group, to verify them. In his tests, Mathias used Siemens new AP3620 access points on 100 meters of Cat5E and pushed as much traffic through them to make sure that both radios would be operating full out. To mix things up, he used two different 802.3af injectors and two 802.3af PoE-enabled switches. He attained throughput of 131 Mbps to 142 Mbps on the 2.4-GHz radio and 116 Mbps to 127 Mbps on the 5-GHz radio, and concluded that the radios were operating using their full capabilities on regular 802.3af.

Siemens success on this point, as noted by other analysts, definitely sets them apart from competitors. This proof point doesn't mean we'll be seeing Siemens creep up to third or even fourth place in Dell'Oro or Synergy's enterprise Wi-Fi market share reports, but it raises the bar for Cisco, Aruba, Motorola, and Trapeze (and Nortel, if its promises for a market entrance in the second half of this year are achieved). If Siemens was able to do this in its first-gen product, enterprises can be confident that within in a year, most everyone else will have a similar product, using newer chipsets and more advanced board designs. In fact, by the time 802.3at-capable switches come to market sometime in 2009, the need for 802.3at in 802.11n APs will almost surely have disappeared.

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