It's common for organisations to find the budget to deploy a wireless LAN to support a single, pressing application. However, once the network has been installed, the enterprise tends to find many other uses for its 802.11 infrastructure, and the network may have not been designed properly to support those additional capabilities.

For this reason, Tom Hagin, vice president of the wireless business practice at integrator NetXperts, in San Ramon, California, advises designing your enterprise WLAN from the outset "for the worst-case scenario, in terms of coverage, capacity and quality, if you have the budget available."

Predict what will be added
For example, when getting started with wireless to support one application, try to predict the workflow of other applications that might get added, he recommends. "The workflow of an IP phone, for example, is much different from that of a bar code scanner," he points out.

"Phones have specific requirements for RF signal strength," he says. He says that -65dBi antenna signal gain is a good target for voice; -57dBi is even better. But -90dBi simply can't support voice, he says.

Hagin recounts the circumstances of one customer with a 2.4GHz Wi-Fi network that wound up with 500 laptops, 500 IP telephones and a capacity bottleneck. "The 2.4GHz band [with just three non-interfering channels] prevented us from cramming more [access points] in" for additional capacity, Hagin explains.

Data in once band, voice in the other
The answer? NetXperts added a 5GHz radio to every wireless access point - Cisco 1200s, which contain 5GHz slots for 802.11a radios and 2.4-GHz slots for 802.11b/g radios. Hagin locked down his customer's laptops to communicate with the 5-GHz
802.11a network only, and the 802.11b IP phones remained on the 2.4-GHz network.

"You do have to lock down [a device you want to operate exclusively on one frequency] or the software will simply connect to the best available network," Hagin explains. Locking down his users' laptops for use only in the 5-GHz band involved simply unchecking the 2.4-GHz option during software configuration, he says.