Environmental Considerations

The environmentbe it a building, country, or climatein which the WLAN operates plays a critical role in defining the architecture and design of WLANs. Chapter 1 introduced the various environmental factors that have an impact on the performance of the WLAN. Examples included the attenuation and distortion of radio signals by various materials and the multipath effect.

The architecture should account for the variables of the environment without actually providing specific details on remediation methods. The design, however, must include specifications on how the WLAN will accommodate local variations.

When defining your WLANs architecture and design, you need to consider the following three environmental matters:

• Physical attributes of the surroundings

• RF environment

• Local governmental regulations

The following sections describe each point in detail.

Physical Attributes of the Surroundings

Physical attributes of the surroundings include both the placement and type of obstacles in open spaces. The obstacles are any foreign objects that the propagating RF signals encounter. The objects can be static, such as furniture, walls, warehouses, and buildings, or dynamic like cars, forklifts, and even people.

The exact type or movement of the obstacle is not important. What is important is that all matter affects the radio signal by modifying the profile and strength of the original signal, which is known as distortion and attenuation, respectively. As the signal's quality and strength decreases, the receiving stations have a harder time reconstructing the original message, and this is accompanied by a reduction in throughput.

Include considerations about the physical environment in your architecture by defining what the minimum acceptable signal quality and strength should be because they determine which throughput your WLAN can sustain. For example, requirements for a signal that must consistently support 54 Mbps throughput will be a lot more stringent than an environment where throughput can throttle between 54 Mbps and 11 Mbps. These guidelines should then be used for the design of the WLAN to determine how many access points are required and where they should be placed.

RF Environment

Physical obstacles are not the only kind of entities that can impact the strength and quality of an RF signal. Other RF signals that are in the vicinity interfere with the original signal and modify its profile.

Whereas the visible concerns can be managed in a straightforward manner, the invisible cannot. Even in controlled deployments, you can expect to contend with other nearby WLAN deployments. Furthermore, devices like wireless phones, microwaves, handheld radios, and Bluetooth devices will have some impact on RF signal quality because (in most cases) they share the same RF space.

The best way to combat the challenge of interference is to carefully and purposely design your WLAN cells. Fix the throughput rate of your cells. Building your WLAN with well-defined cells aids in the control and troubleshooting of these unknowns. An additional benefit of carefully controlling the footprint of the radio cells is a higher degree of security. Chapter 7 covers the security considerations in more detail.

WLAN protocols are designed to throttle throughput in function of the strength and quality of the signal. As the footprint of the cell is related to the throughput, varying rates result in changing cell sizes. For example, in 802.11b, cells that are fixed at 11 Mbps are significantly smaller than those that are fixed at 2 Mbps. Pegging the throughput rate creates a fixed cell-size that is an easier to use building block for designing your WLAN. The ability to design the network with standard and well-known parameters also makes it easier to set the expectations of the user and troubleshoot the WLAN.

Local Governmental Regulations

One of the most overlooked aspects of WLANs in the global enterprise is the different regulations and limitations that are imposed on WLANs and, specifically, the RF spectrum in which they operate. Regulations surrounding RF are managed by both national and regional bodies, and significant disparities can exist between respective local regulations. Be aware of potential differences in RF regulations and know which regulatory bodies are relevant in your specific case and where to consult upon them. Include both the regulatory requirements and the correct local solutions in both your architecture and design.