An extremely beneficial aspect of Wi-Fi networks is mobility. For example, a person can walk through a facility while carrying on a conversation over a Wi-Fi phone or when downloading a large file from a server. The 802.11 radio inside the user device automatically roams from one access point to another, as needed, to provide seamless connectivity.
In general, wireless technologies provide access point roaming protocols. For example, with 802.11 networks, the client radio makes a decision to hand off to the next access point when retransmissions and received signal levels indicate a need to hand off. A decision to hand off too soon generally leads to skipping back and forth between access points. As a result, client radio manufacturers generally choose to dampen the handoff process and wait until it is absolutely necessary to hand off to the next access point.
Every model radio device behaves differently when roaming because of proprietary mechanisms, and some cards do better than others. Keep in mind that roaming might take much longer than expected with WLAN applications, especially wireless voice applications, which are not tolerant to roaming delays exceeding 150 milliseconds. The use of wireless middleware can also help accommodate patterns of broken communications between the client and the server caused by roaming delays.