Designing Peer-to-Peer WLANs
Designing a peer-to-peer network involves three main considerations. First, the station must be arranged so that they are all within the proper distance limits. Second, all -stations must send and receive signals on the same transmission frequency. And finally, the hidden node problem must be avoided so that each station can communicate with all other stations. range. However, Stations B and D are not within the range of one another and thus cannot send and receive messages. These two stations would have to move closer together in order to communicate.
Most wireless NICs have a factory-set default frequency. However, some vendors do not allow this setting to be changed, which could lead to interoperability issues between vendor products.

  Designing Infrastructure Mode WLAN
The most important questions in the design of an infrastructure mode WLAN are: how many access points are needed and where they will be located. Other design discussions for infrastructure WLAN include whether to set up access points as "cells" within the same network or as a separate network and how to address "handling off" users from one access point to another or from one network to another.
Access points
The number of access points needed depends upon many different factors, including: Area of coverage
•      Number of supported users
•      Network utilization
Physical obstruction or radio interference.
As with peer-to-peer networks, stations that are farther away from an access point will have slower transmission speeds as shown in Figure

Adding additional access points will decrease the distance between stations and the access points, which will, in turn, provide users with higher bandwidth.

The second factor is the number of supported users. Although a single access point can support between 250 and 300 users, in actual practice the number should be fewer. -adding more access points will increase the throughput of the WLAN because fewer
users will be contending for access. Another factor is the network utilization; frequently, transforming large files over the WLAN would result in heavy utilization while. accessing only e-mail would be light utilization. Heavily utilized networks will perform much better if more access points are added. Finally, the number and type of physical obstructions and the noise levels in the radio frequencies can reduce the coverage area. Adding more access points can create broader areas of coverage.
Just as important as how many access points are used is, where they will be located. A single access point should be placed as close as possible to the centre of the plwnned coverage area. If it is necessary to install the access point in an obstructed
location, an optional range extender antenna can be mounted to extend the coverage area.
A range extender antenna should also be used if the access point needs to be intalled in a closed location (such as a closet) for security reasons. Some access points receive electrical power over the same cable that connects the access point to the wired network. This feature eliminates the need to run a power wire to the access point that may be located on the wall or ceiling, making the installation quicker and less costly.

When selecting location for multiple access points, it is important to remember that each coverage area must overlap another coverage area to allow roaming for the stations. The amount of overlap depends on the number of users in a coverage area and the utilization of the network. If one coverage area has more users or heavier network utilization than other coverage areas, overlap of the adjacent coverage areas may be increased by moving the access points closer together.

However, if more users move to the area covered by access point 2, then shifting access point 3 to cover some of that additional area will spread out the load because some station will then connect to access point 3 instead of access point 2. It is also important to be aware of potential hidden station problems. Stations should be arranged to minimize or prevent any two clients from being within the range of the access point but out of the range of each other.

Most WLANs have a software utility known as a site survey that assists in the placement of access points. It will display such information as the single level, the outside noise level, and the signal-to-noise ratio (SNR), which indicates how much of the signal is being affected by noise. Some site survey tools use colour-coded bars to indicate when the communication is poor, fair, good, or excellent.
Using a laptop computer on which the site survey software is running, a user roams through the coverage area. A low signal level indicates that the access points may be too far apart. The solution may be to relocate or add access points. If the noise level is high, a user can walk through the area, monitoring the noise level indicator to determine the exact location of the source of interference. It may be necessary to switch off the source of the interference or relocate it.
Site survey tools may be used when initially installing the access points. They may also be used on a regular basis to determine whether the coverage areas change due to new obstructions or new sources of radio interference.

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