A method is provided for managing transmissions among nodes communicating over a shared communication medium. The method includes: transmitting a frame from a sender node to a plurality of receiver nodes, the frame including at least a portion of a data packet and control information associated with accessing the communication medium; transmitting over the communication medium information indicating an end of a time window allocated for transmission of acknowledgement signals to the sender node from at least some of the plurality of receiver nodes; assigning each of a plurality of time slots in the time window to different subsets of the plurality of receiver nodes; and for a given receiver node, transmitting an acknowledgement signal from the given receiver node to the sender node during a time slot assigned to the given receiver node, the acknowledgement signal responsive to at least the frame.