A beacon is a wireless LAN packet that signals the availability and presence of the wireless device. Beacon packets are sent by APs and base stations. However, client radio cards send beacons when operating in computer-to-computer (ad hoc) mode.
These beacons must be acknowledged back and forth between two communicating devices. The devices may disassociate from each other if a series of beacons is missed.
The Access Point (AP) does not force disassociation if the client does not respond to beacons or if the client misses one beacon. It only disassociates a client when it does not respond to data packets sent by the AP. However, this behavior is client specific. As far as Cisco clients are concerned, they disassociate or roam to another AP when they miss eight consecutive beacons.