Wireless LAN FAQ

Computerworld - Wireless LANs are finally venturing out of their vertical market niches and into mainstream business environments. But they pose some special deployment challenges when compared with their wired counterparts.

Here are six frequently asked questions IT managers should consider before installing a WLAN.

1. How do I plan capacity for a mobile network? Wireless experts suggest that you first identify which applications the network will support and how much bandwidth they will consume. Then calculate how many users need mobility and in what places within your organization they will require it.

Next, apply this information in designing a network of wireless access points (AP). APs are the infrastructure radios, usually ceiling-mounted, which connect to the wired network on one side and to users' wireless network adapters over the airwaves on the other. Wireless veterans stress the importance of site surveys and performance testing to optimize AP placement.

"This is because variations in firmware, antennas and physical layout can alter the performance and range of the very same [wireless] chip set," says Craig Mathias, an analyst at Farpoint Group in Ashland, Mass.

Because it's difficult to anticipate where walls and objects will interfere with wireless communication, a network staff member armed with a wireless laptop typically walks around, installs APs and tests coverage—often trying out multiple antenna options for maximum signal strength.

This exercise will reveal how many APs you need to meet capacity requirements and how to position adjacent APs to prevent coverage holes. There are some rules of thumb about how many users a single AP can support. Gartner Inc., for example, recommends about 20 knowledge workers per 802.11b (11Mbit/sec.) radio.

But these ratios vary. Warehouses often need lots of APs to ensure floorwide coverage. But warehouse applications don't consume much bandwidth, and utilization of these APs is often only 2%, says Rob Greenfield, chief scientist at SCLogic Inc., a reseller of WLANs in Beltsville, Md.

On the other hand, a crowded office space will require many more APs—not to achieve range, but to support more users and heftier applications.

"Shoot for under 40% to 50% AP utilization in office environments," Greenfield suggests. That will compensate for not knowing how many users will be in range at any given time.

2. How can I avoid interference? Having multiple devices that use the same frequency can result in interference with performance. United Parcel Service Inc. learned this when it combined short-range Bluetooth (1Mbit/sec.) wireless technology with 802.11b LANs in a warehouse pilot, explains Joan MacEachern, lead telecommunications analyst at the Atlanta-based worldwide package-delivery company. Both Bluetooth and 802.11b run in the 2.4-GHz frequency band.