Is there such a thing as a technology that's too easy to implement? I never thought so until I helped an organization plan for a wired-LAN—to—wireless-LAN (WLAN) conversion as part of an office move. I initially thought we'd knock out the job in half a day—we'd go to the new office building to look at the physical premise, pick a few spots for wireless Access Points (APs) and the necessary wiring, select a vendor, and be done in time for lunch. However, as we got deeper into the project, I began to realize everything that you must consider to properly plan a Wi-Fi WLAN implementation.
Having some experience setting up Wi-Fi APs in my home and the homes of several friends, I'd fallen into a common trap—I viewed Wi-Fi as simple to implement with relatively good performance, regardless of its use. Of course, these small-scale implementations were in locations covering only a couple of thousand square feet and supporting no more than three or four users.
And so the revelation began. When you're planning to deploy Wi-Fi in the enterprise, you must consider bandwidth, interoperability, security, scalability, radio frequency (RF) interference, and several other technical details, not just which gear has the best feature-to-price ratio. And in addition to technical and physical considerations, you must account for budgetary constraints and physical limitations when placing equipment. Let's look at what you need to do to prepare for Wi-Fi so that you can avoid the common pitfalls.
Choosing the Right Wireless Standard
Every wireless standard brings unique advantages, along with certain drawbacks, to wireless networking. So, your first step is to decide whether you'll implement an 802.11a or 802.11b WLAN or wait for 802.11g, which recently became a standard. 802.11g provides the range and cost of 802.11b and maintains the speed of 802.11a. For details about the various wireless protocols, see "Related Articles in Previous Issues."
Choosing the Right Gear
With so many wireless vendors to choose from, how do you know which one to use? After all, all Wi-Fi gear must be interoperable to receive Wi-Fi certification, so you might think they all provide roughly the same capabilities, right? Wrong. The core capabilities are the same across all the equipment, but the implementation, management, and administration of those capabilities vary greatly. As a result, you might end up selecting one vendor over another depending on which features are most important to you.
When you're selecting a Wi-Fi AP, make sure you can add an external antenna. Integrated-antenna systems are fine for home use, but they aren't appropriate for enterprise implementations because in general their effective range isn't as far-reaching. Other physical considerations include mounting options and whether the AP supports Power over Ethernet (PoE), which can make the job of providing power to your AP much easier.
On a technical level, some vendors include in their products additional features and functionality that extend the 802.11 standards. One of the most common features is the ability to increase the effective bandwidth when you pair a particular manufacturer's AP with its own network adapters. For example, Linksys claims that its WAP54A 802.11a AP offers 72 Megabits (Mb) of throughput when you use the product's "turbo mode" in conjunction with Linksys-brand adapters.
Several other features to consider fall under the realm of security. For example, I typically advise my clients to consider only those APs that can restrict access based on preauthorized media access control (MAC) addresses. This functionality prohibits rogue network adapters from freely associating with your network. Although an intruder with the right tools can work around this restriction, it still acts as a deterrent. I also recommend looking for APs that let you disable beaconing—the default behavior of most APs to broadcast its Service Set Identifier (SSID) at regular intervals. This behavior lets anyone within range know that you have a wireless network available for use. Like MAC address restrictions, you can't disable beaconing all the time (there are still certain times when the SSID will pass through the air in the clear). However, the ability to turn this feature off improves Wi-Fi security.
Determining How Much Gear You Need
When determining how much equipment you need, the first part of the equation—selecting the client network adapters—is easy. Obviously, you need one adapter for each desktop or laptop that will access your organization's WLAN. Depending on your topology, you might need to expand your wired network infrastructure to support the addition of APs throughout your organization. Determining how many APs to purchase is more complicated. When you're making this decision, you need to weigh several factors, including user density, physical topology, and bandwidth requirements.
User density is relatively straightforward. One AP can typically handle a set number of users. For example, according to the manufacturer, the Linksys WAP54A 802.11a wireless AP can handle 64 users at a time. If you plan to provide wireless access in a high-density user area, at a minimum, you need to divide the number of users by your AP's maximum capacity to come up with a starting number.
Keep in mind that in the United States, only 11 channels are approved for use in 802.11b wireless networking equipment. Because adjacent channels overlap each other to a certain degree, you can't set one AP to use channel 1 and another to use channel 2 unless enough distance exists between them so that their signals don't overlap. Three channels (1, 6, 11) are far enough apart that they won't overlap. Alternatively, 802.11a equipment uses three separate 100MHz domains. The lower two frequency ranges are designed more for indoor use and allow for eight nonoverlapping channels. The upper frequency range is designed for outdoor use and, therefore, provides only four non-overlapping channels.
When you're reviewing the physical topology, keep in mind that certain physical obstacles provide varying degrees of resistance to RF signals that travel from the AP to the client's workstation. Some obstacles might prevent the RF signal from getting through at all, which would require another AP to provide adequate signal coverage for that area.