A method of controlling a data unit sender (Fig. 10: 100) that comprises a data unit buffer for holding data units of a communication protocol and is arranged to act as a sending peer of said communication protocol, where in accordance with said communication protocol said data units are arranged in a sequence and each sent data unit is identifiable by a sequence position identifier, and feedback messages, using said sequence position identifiers, carry information on a receipt of said data units, said communication protocol providing for at least a first type and a second type of receipt information, said first type of receipt information being indicative of a correct receipt of a data unit at a relay peer of said communication protocol, and said second type of receipt information being indicative of a correct receipt of a data unit at a final destination peer of said communication protocol, said method comprising: performing a first retransmission control procedure (S123-S126) for a given data unit in said buffer that has been sent but for which no first type receipt information has been received, performing a second retransmission control procedure (S128-S132) for said given data unit if first type receipt information has been received for said given data unit, and holding said given data unit in said buffer at least until having received said second type of receipt information for said given data unit, wherein said first retransmission control procedure comprises starting to monitor a first time-out period upon transmitting said given data unit and retransmitting said given data unit if said first time-out period passes without receiving first or second type receipt information for said given data unit, and wherein said second retransmission control procedure comprises starting to monitor a second time-out period upon transmitting said given data unit or upon receiving first type receipt information for said given data unit, and retransmitting said given data unit if said second time-out period passes without receiving second type receipt information for said given data unit, the method further comprising dynamically adapting said first time-out period based on measurements of a time that passes between a transmission of at least some of said data units and a receipt of respective first type receipt information, and dynamically adapting said second time-out period based on a measurement of a time that passes between a transmission of at least some of said data units and a receipt of respective second type receipt information. performing a first retransmission control procedure (S123-S126) for a given data unit in said buffer that has been sent but for which no first type receipt information has been received, performing a second retransmission control procedure (S128-S132) for said given data unit if first type receipt information has been received for said given data unit, and holding said given data unit in said buffer at least until having received said second type of receipt information for said given data unit, wherein said first retransmission control procedure comprises starting to monitor a first time-out period upon transmitting said given data unit and retransmitting said given data unit if said first time-out period passes without receiving first or second type receipt information for said given data unit, and wherein said second retransmission control procedure comprises starting to monitor a second time-out period upon transmitting said given data unit or upon receiving first type receipt information for said given data unit, and retransmitting said given data unit if said second time-out period passes without receiving second type receipt information for said given data unit, the method further comprising dynamically adapting said first time-out period based on measurements of a time that passes between a transmission of at least some of said data units and a receipt of respective first type receipt information, and dynamically adapting said second time-out period based on a measurement of a time that passes between a transmission of at least some of said data units and a receipt of respective second type receipt information.