In a communication system where a primary cell is controlled by a first base station and a secondary cell is controlled by a second, different base station, flow control is performed between the primary cell and the secondary cell for data for a radio link control layer. According to the flow control, the data for the radio link control layer is communicated between the first and second base stations using a link between the first and second base stations. Flow control may be performed between the primary cell and the secondary cell by dynamically controlling a depth of queued radio link control data in the secondary cell for one or more UEs based on one or more factors, e.g., current/future loading of secondary cell, peak theoretical throughput for a UE in the secondary cell, and/or a UE's current channel quality information. Apparatus, methods, and computer program products are disclosed.