802.11n's unsolved power problem

Not every vendor has developed 802.11n access points that can be powered using Power over Ethernet, partly because standards explaining how to do so are thin on the ground.

 Before deploying 802.11n Wi-Fi technology, organisations must determine whether their vendor of choice has developed access points that can run on electricity supplied by Power over Ethernet (PoE).

Access points built to the soon-to-be-ratified 802.11n standard generally require about 15.4W to power their dual-radio, 3x3 MIMO functionality. Many enterprises power their access points with PoE. Since the current PoE standard, 802.3af, carries only 12.95W of power, many organizations could find themselves in a mess if they pick the wrong vendor.

Luc Roy, vice president of enterprise mobility at Siemens, said this is a critical issue for companies. About 80% of his customers power their Wi-Fi deployments with PoE, he said. It's cheaper than running AC power cables in the ceiling of an office.

"[The PoE issue] doesn't necessarily have to inhibit implementation, but it will certainly affect your decision or choice of vendor," said Mark Tauschek, senior research analyst with the Info-Tech Research Group. "If you're thinking about it ahead of time, your short list of vendors will be slightly different than it would be otherwise."

The IEEE is expected to ratify a new standard of PoE, 802.3at, near the end of this year. The 802.3at standard would allow Ethernet to carry 56W of power to devices. This would seemingly solve the power problem, except that installing new cable and switches on the new standard will be an expensive proposition. And many organizations want to deploy 802.11n now.

So, in the meantime, vendors are taking different approaches to make 802.11n access points run on the current PoE standard. Some are advising customers to run a second Ethernet cable to each of the access points. Pulling more cable to access points can be an unwelcome financial hit for companies that have already paid someone to install one run of cables.

Roy said that having to revisit PoE infrastructure could double or triple the cost of an 11n deployment. "One customer suggested that to swap in an 11n access point is about $200," he said. "In this particular case, you've got union workers. If you have to go and revisit and pull another cable, you have to bring in an electrician on that. Then the cost can go up well over $500."

"[Another] option is to reduce the feature set on the access point in order to bring the power requirement down," said Michael Braatz, vice president of marketing at Bluesocket, a manufacturer of wireless networking technology. "Manufacturers can reduce the transmit power of the radio so the effective coverage range of the radio, instead of being 100 feet indoors, is maybe now only 50 feet. You take away some of the inherent benefits of 11n by doing that."

Cisco Systems has introduced Enhanced Power over Ethernet, a proprietary standard that delivers enough power to support full-featured 11n access points.

"I never like proprietary standards," Tauschek said. "I don't like it when Cisco does that, but the truth is they're the only ones who can. Who else can say we own 70% of the LAN switching and PoE market? They're in a position to say, 'We can offer our installed base and potential customers a solution consuming more than 15.4W with enhanced PoE,' whereas no other vendor could do that."

But then users are locked into a proprietary standard, Tauschek said.

Other vendors are relying on innovative engineering to make their access points more energy efficient.

"Power consumption on the radio is a combination of three things," Braatz said. "One, is which components you pick to go in your access points, because component parts draw power differently; two, it is a function of the radio chip you pick; and three, is the software architecture."

Careful work with these three components has allowed Bluesocket to produce 11n access points that draw less than 12.95W, Braatz said. Other vendors, such as Siemens and Aruba, have also developed access points that can be powered by the current PoE standard.

Tauschek said vendors are certainly running up against the edge by engineering their access points to run on PoE. "I think they're pushing against the bounds of the 802.3af standard," he said. "How robust can it be? I think that's a valid standard. But they can be pretty clever, those engineers, and they can figure out ways to consume a little bit less power."

Craig Mathias, founder of the research firm Farpoint Group, recently tested Siemens' 802.11n access points and found that they can run on the current PoE standard.

"I've talked to other vendors and they say, 'Stand by, we'll have access points that run on 802.3af power,' " Mathias said. "It's not impossible to do. It's just difficult to do. Because no matter what you do, you need a certain number of components to build an access point. And the components that are available to do it are up against the ragged edge for what's allowed on the current PoE standard."

Enterprises should watch out for vendors that compromise on features and performance in order to fit the PoE standard, Mathias said.

"It's still early," he said. "I think the second generation of products is going to be just remarkable."

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