In a wireless local area network system including a server and a plurality of mobile wireless stations, the server maintains a table of stations active in the network system and monitors the transmission activity of the stations. If no activity is detected from a station for a predetermined time, a series of watchdog messages is sent requesting a response from that station. The stations are battery powered and operate in an "AWAKE" state to receive or transmit messages or in a SLEEP state of low power consumption. The stations return from the SLEEP state to the AWAKE state in time to receive at least one watchdog message, thereby avoiding the stations being undesirably logged out from the table of active stations.