The power complaint from some IT managers has been that the current Power over Ethernet (PoE) standard, 802.3af, won't provide sufficient wattage over a single Ethernet cable to power two different radios and a 3x3 Multiple Input Multiple Output (MIMO) antenna configuration in an 802.11n access point. (The 3x3 refers to three antennas on each of the two radios.) Farpoint noted that reducing processing in an access point, by shutting off one of two radios or reducing the 3x3 MIMO configuration to 2x3 MIMO, might draw less wattage than provided in the 802.3af standard which would be "clearly undesireable." The consulting firm added, "We see no point in installing .11n only to reap a less than optimal return on investment and the promised improved ... performance."
Analysts said they have seen IT managers string a second Ethernet cable to a new 802.11n AP to bring added PoE. One IT manager at a university couldn't afford to string more Ethernet cable and simply plugged a new AP into a wall socket nearby, said one analyst who asked not to be named. Farpoint didn't name companies that have failed to power new 802.11n APs with a single PoE Ethernet cable, but said Siemens had passed the test.
Roy said some customers seem to be waiting for a proposed PoE-plus standard that more than doubles the wattage going through a single cable. However, using PoE-plus will require a major infrastructure change that Siemens argues could be expensive and is not necessary when using their gear.
To achieve truly faster speeds with 802.11n access points, Roy said IT managers may need to put legacy 802.11a/b/g laptops and other clients on a 2.4GHz radio inside of each new 802.11n AP, while reserving the 802.11n clients for the other radio running at 5GHz, completely separate from the 2.4GHz.
Running both fast and slow clients over a single radio will slow down the faster traffic to the speed of the slower traffic, he said. "It's like a car driven on a single lane highway at 70 miles an hour, being passed by a car only doing 50 that slows down the faster car until it gets out of the way," he said.
Recognizing how complicated the implementation can be and that adjustments are needed to accommodate 802.11n for maximum performance and power conservation, Siemens has written a white paper for IT managers, "Practical Considerations for Deploying 802.11n" that details some of the tricks needed to make 802.11n function well.
Aside from such tactics, IT managers also need to take stock of wireless LAN networks in general, now that 802.11n is clearly catching on, Yankee's Hochmuth added.
"Enterprises need to look at what they use WLANs for," Hochmuth said. "With .11n coming, they need to check on what they are doing with wireless, whether it is a redundant overlay of the [wired] LAN, or whether it can be used for specific things such as network access for building visitors. They need to ask, really, has the air become the new category 5 cable?"