Introduction

Unless you are setting up a WLAN in your home or very small business, your wireless network will include more than one AP. Because each AP provides RF coverage to a limited area, you will need many of them to provide complete wireless connectivity in the office building, airport, or warehouse. Even if your intent is to provide connectivity for users in only one particular area to create a hotspot, deploying multiple APs configured for different RF channels will increase effective radio bandwidth and the number of simultaneous users your network can support. In the business environment, you can encounter WLANs with hundreds of APs. Examples of such WLANs include organizations that occupy an entire Manhattan skyscraper or have a large campus with multiple adjacent buildings. Usually if a company decides to deploy a WLAN, it opts for complete wireless connectivity throughout the organization s real estate to provide complete mobility for its workforce.

The process of a wireless client moving from one wireless cell to another wireless cell is called roaming. As we will learn later, the user might roam even if he or she does not physically move. If, after the association with the new AP, the client stays connected to the same IP subnet or virtual local area network (VLAN) as before, we call this L2 roaming. If after the roam the client ends up on a different IP subnet or VLAN, we call it L3 roaming. In a large, well-designed WLAN, the user s...