A method and apparatus for limiting the length of a service period in a Wireless Local Area Network (WLAN) including an Access Point (AP) and at least one station is presented. A maximum service period (SP) length for at least one station is determined. A value in a max SP length field in a control field of an uplink frame sent from said station to said AP is set. The value of the max SP length field is determined at the AP. Frame transmittal from the AP to the station is triggered during a service period when the value is non-zero, while downlink frame delivery from the AP to the station is prevented when the value is zero.