According to a method for reducing a risk of transmission stalling between a transmitting unit and a receiving unit, data blocks are transmitted to the receiving unit from the transmitting unit. Each data block includes a block sequence number (BSN). The transmitted data blocks are stored in a transmission buffer. A flow of retransmission of transmitted data blocks is controlled with a transmission buffer window comprising an acknowledge state variable (ASV) that contains the BSN value of the oldest data block that has not been positively acknowledged by its peer. If a BSN corresponding to the ASV is acknowledged in a first type of acknowledgment message, a status of the BSN is set as tentative acknowledged. If the block sequence number is acknowledged in a second type of acknowledgement message, the status of the BSN is set as acknowledged, and the transmission buffer window is advanced to the ASV.