A wireless LAN is comprised of a number of wired infrastructure devices, including at least one access point able to support a number of wireless communication devices configured to operate in the U-APSD mode. The wireless communications devices periodically contending for the wireless medium to transmit trigger messages to the access point and the access point responding by transmitting at least one frame of information. The wireless communications devices operate to synchronize the transmission of their trigger messages such that the possibility that the messages collide with one another is minimized.