Counting the Radios for Capacity
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You used to buy one access point (AP) and expect one radio inside -- but thats so old-fashioned. How about four radios?
Extricoms new EXRP-40 UltraThin Access Point has that many radios in a single enclosure, and the company claims it is an industry first.
More notably than more electronics in the box is what they enable, says David Confalonieri, vice president of marketing at Extricom. The company uses same band operation on its networks, using one radio per AP to help provide a blanket of coverage on a single channel. With dual radios, it had two channel blankets. With one switch connected to a constellation of these [new APs], well build four overlapping channel blankets, Confalonieri says. He says this quadruples the capacity of the networks.
Well, thats been done for a while now, by Xirrus. Their Wi-Fi Array is a large circular device with that many Wi-Fi radios inside. Xirrus even went so far as to issue a statement saying it welcomes copycat attempts by Extricom, Trapeze and Meru. The latter two have their own dual-radio APs which dont stack their capacity like Extricom; Meru also sells what it calls a Radio Switch with multiple radios built in. Foundry Networks
resells a version of that Radio Switch as well.
Confalonieri says the difference from Extricom is that Xirrus has the equivalent of 16 fat APs in the box, while its UltraThin APs have little in the way of smarts -- they connect back to a controller. Plus, the Xirrus Wi-Fi Array is sectorized. If its in the conference room, Im in the northeast corner of the room, I talk on one radio -- in the opposite corner, its a different radio, he says. Each radio is serving a pizza pie piece of the room.
Of course, Xirrus tends to sell its Array one to a floor to serve a large number of people. It would likely take a few UltraThin APs to get the full coverage for a building floor.
Extricom plans to continue selling its current APs -- the two-radio version is $495, so extrapolate what you will for the as-yet undetermined price of the four-radio version. Firmware to come will eventually let the four-radio AP work on the same switch as the dual, to help protect customers current investment.
At the moment, Extricom hasnt made any specific announcement about 802.11n support, saying it wants to work within the standard, while also claiming its channel blankets can outperform 11n.
Xirrus has announced 11n plans, however. In fact, it's demonstrating its 3x3 MIMO 802.11a/b/g/n Radio Module for the Wi-Fi Array this week at Interop in Las Vegas. The company plans to have it in beta before the end of this year. If a customer puts 16 of these modules in an array (which come in 4-, 8- and 16-radio versions), Xirrus says the overall capacity will be 2 Gigabits per second (Gbps) of aggregate bandwidth (that means using six bonded channels pairs in the 5 GHz frequency and one pair in 2.4 GHz).
Earlier this month, Xirrus announced that the Wi-Fi Array had received further Wi-Fi Alliance certification for security, supporting Wi-Fi Protected Access 2 (WPA2) with extended Extensible Authentication Protocol (EAP) types. The Array is also going to support Power over Gigabit Ethernet. With that many radios, the Array needs more juice, so its new high-power PoE will tap 60W. This is the first time Xirrus has supported any PoE