WLAN components and topologies
Now, let's take a look at the typical components that make up a basic WLAN solution. It's important to remember that wireless local area networks are just that -- local. They are used within a single building or in a campus area building-to-building connection. WLANs are most often used on mobile systems as an extension to a wired LAN, as illustrated in Figure A.

Figure A

Example of a standard wireless LAN topology

You need to be familiar with three types of WLAN components:

• Wireless network cards
• Wireless access points
• Wireless bridges

Wireless network cards come in a couple of flavors, including a PCI card for workstations and PC cards for laptops and other mobile devices. They can act in an ad hoc mode, as in client-to-client, or in a pure client-to-access point mode. In an ad hoc mode, the wireless network card is configured to talk with other wireless network access cards that are within its range. This functionality will vary depending on the product and the 802.11 specification being used. Client-to-client (also known as peer-to-peer) WLANs are useful for small roaming workgroups of desktops or laptops that do not require access to the LAN backbone. The plug and play capabilities of most wireless network cards make this type of setup rather simple. Most wireless network cards will connect to an access point. An access point is essentially a hub that gives wireless clients the ability to attach to the wired LAN backbone. The use of more than one access point in a given area is facilitated by the use of cell structures, which are similar to what cell phone providers use to maintain your coverage area. A site survey can determine where to place access points within a building to create a map of the areas (cell structures) that will require wireless LAN access. The data transfer rate for each wireless client will be determined by its location within the cell structure. Locations closer to the center of an access point radius will experience higher throughput than those that are closer to the outside of the cell coverage area. This is facilitated by auto shifting, which allows the data rate to downshift based on distance from access point. Again, this functionality will vary depending on the product and 802.11 standard used. One of the greatest benefits to roaming mobile users is the ability for one access point to hand off communication to the next access point in the roaming cell. Known as seamless roaming, this allows the user to move from cell structure to cell structure without losing connectivity to the network.