When transmitting medium access control protocol data units for the high speed downlink shared channel over a plurality of hybrid automatic repeat request processes, one of the processes can be in a retransmission procedure. In this case, stalling of the transmission can occur, because the medium access control layer for the high speed downlink shared channel of the receiver apparatus (3) buffers the following packet data units, when a preceding protocol data unit is waiting in the stalled process. To enable an early processing of the already received data, the receiver apparatus determines, whether the next expected service data units for a higher layer such as a radio link control layer, are included in the already received packet data units by taking into account the sequence number for the higher layer. Therefore, the medium access control layer for the high speed downlink shared channel accesses the data of the service data unit for the higher layer.