Article

Wireless LAN architecture: Enterprises leaving 2.4 GHz for 5 GHz

Shamus McGillicuddy

As enterprises roll out a new wireless LAN architecture based on 802.11n, the legacy wireless LAN frequency 2.4 GHz

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is starting to resemble a sinking ship. Nearly everyone is trying to jump off.

"We are trying to abandon 2.4 GHz," said Victoria Poncini, a wireless LAN architect for Microsoft who is designing and rolling out a new network of 15,000 802.11n Aruba Networks access points (APs) and 450 controllers globally. "Basically, we enable both 2.4 GHz and 5 GHz on our APs, and we deploy them ubiquitously throughout the campus. However, we are moving as many clients as we can to the 5 GHz band. We are using Aruba firmware that allows us to specify band preference, and if a client refuses to move for some reason, we will let them stay on 2.4 GHz."

The bulk of 802.11n wireless LAN architecture deployed today comprises a large number of dual band wireless LAN APs. Most of these APs have one radio operating at 2.4 GHz and the other at 5 GHz. The 5 GHz wireless LAN frequency has historically been maligned because of a basic assumption of physics: the higher the frequency of a radio, the shorter the range. Logic dictated that if 5 GHz wireless LAN radios had shorter range, then a network would require more APs and thus be more expensive.

Craig Mathias, principal of Farpoint Group, a wireless networking research firm, says that this concern is unfounded since most enterprises are no longer trying to test the outer range of their APs. "At any given throughput, the range of 5 GHz is just as good as 2.4 GHz. The overall maximum possible theoretical range is probably lower, but we're not optimizing for range anymore. We're optimizing for capacity, so it doesn't make sense to think along those lines anymore."

Still, many enterprises retain a bias against a wireless LAN architecture that favors the 5 GHz wireless LAN frequency because of concerns about its range .

"A lot of people are not aware of 5 GHz as a viable option," Mathias said. "We still run across even large enterprises [that] have not done a lot with wireless LAN [which] think that three channels at 2.4 GHz is all you need."

Choosing wireless LAN frequency: Is 2.4 GHz too noisy?

If you're trying to design a wireless LAN architecture that will serve as the primary access layer in your campus network, however, 2.4 GHz won't be all you need. The 5 GHz wireless LAN frequency has more capacity and is freer of interference, mainly because it usually has nearly a dozen non-overlapping channels compared with the three available in the 2.4 GHz frequency. The channels available for use in 5 GHz vary by country because many of them are regulated frequencies, but even just a dozen channels make it easy for APs to avoid co-channel interference and also allow enterprises to practice channel bonding, which enables higher throughput.

More on wireless LAN architecture and WLAN radio frequency:
A research report examines the 2.4 GHz vs. 5 GHz debate.

How to upgrade the wireless LAN for mobile applications.

Learn about the current state of wireless network standards.

Are fat access points making a comeback in wireless LAN architecture?

Meanwhile, the 2.4 GHz frequency is a noisy place, with APs contending with a cacophony of interference from other sources that usually don't reach the 5 GHz frequency: Bluetooth radios, microwave ovens, cordless phones, and rogue consumer-grade APs competing for airtime.

"In certain areas [of my network], I had to shut off some 2.4 GHz radios because of co-channel interference with adjacent radios," said Ammar Abdulahad, applications analyst with Lawrence Technological University in Southfield, Mich. He manages a network of 100 wireless LAN arrays from Xirrus Networks, a vendor that specializes in serving high-density wireless users. Xirrus arrays have self-contained controller functionality and hold between four and 24 wireless LAN radios. The first four are tunable between 2.4 GHz and 5 GHz, and the others are fixed at 5 GHz.

Abdulahad uses this Xirrus approach to wireless LAN architecture to deploy a higher ratio of 5 GHz wireless LAN radios in his network.

"We use more 5 GHz radios because of interference issues [in 2.4 GHz]," he said. "We noticed that the throughput is higher when the connection is 5 GHz, even when it is in the same array as a 2.4 GHz connection."

A wireless LAN architecture without 2.4 GHz?

Despite the problems, large enterprises won't immediately abandon 2.4 GHz, mostly because of the ongoing presence of legacy Wi-Fi clients. Untold numbers of laptops, smartphones and other Wi-Fi-enabled devices are equipped with 802.11a/b/g wireless chipsets that can communicate only in the 2.4 GHz band. Even some of the latest and greatest 802.11n gadgets are 2.4 GHz only.

"Take the iPhone 4.While it's an 802.11n device, it works only in 2.4 GHz. There are many, many devices that simply don't operate in the 5 GHz frequency," said Chris Kozup, senior manager for mobility solutions marketing at Cisco Systems. "It comes down to a question of cost.… The silicon for these devices is less expensive than 5 GHz silicon. It's changed a lot in the last several years, but when you get to smaller devices with larger radio requirements, a single radio that support 2.4 GHz versus 5 GHz consumes less power and is less expensive."

Many Wi-Fi clients, whether 802.11n or something older, default to the 2.4 GHz band. Wireless LAN infrastructure vendors recognize that 2.4 GHz is crowded and noisy, and many have built capabilities into their wireless LAN architecture that instruct a wireless client to connect in 5 GHz instead of 2.4 GHz. Cisco has BandSelect, and Aruba has a band steering feature in its Adaptive Radio Management software.

In Microsoft's Aruba network, most users are connecting via 5 GHz, but 2.4 GHz is still up and running, Poncini said. In fact, she has mostly reserved the 2.4 GHz band for a certain class of devices, such as phones, Zunes and wireless Xbox connections. "We also use 2.4 GHz for guest access," she said. "And even though you try to push them to 5 GHz, there are some clients that just stay in 2.4 GHz. We don't want to deny access to any of those clients."

Let us know what you think about the story; email: Shamus McGillicuddy, News Editor


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