The present invention provides a method for specifying actions that a receiver takes upon receiving an AM or UM PDU with an error indication. Currently, for RLC acknowledged mode (AM) and unacknowledged mode (UM), upon receiving an AM or UM PDU with an error indication, actions that the receiver takes are not specified. Inappropriate actions that the receiver takes can cause serious problems. For example, unnecessary reset procedures are initiated, unnecessary retransmissions are made, data is lost, or synchronization between the sender and receiver can be lost. In an embodiment of the present invention, for RLC AM, upon receiving an AM PDU with an error indication, the receiver discards this PDU. In another embodiment of the present invention, for RLC UM, upon receiving an UM PDU with an error indication, the receiver discards this PDU. In another embodiment, MAC discards a MAC SDU that is to be delivered to an AM or a UM RLC entity, if an error indication for this SDU has been received from the lower layer. As a result, radio resources are not wasted, unnecessary retransmissions are avoided, synchronization is maintained, and data loss is prevented. Therefore, by utilizing the present invention, wireless communication system performance is improved.