In general, the subject matter described in this specification can be embodied in methods, systems, and program products for adaptive data unit transmission. A sliding window is filled with data units and designates a sliding window start position and a sliding window end position. A value for each of the data units in the sliding window is stored, the value representing a maximum number of times that each data unit is to be transmitted. The stored value is different among at least two of the data units. Data units are selected from the sliding window to be assembled into a packet. An assembled packet is transmitted to a receiving computerized device. A determination that the data unit positioned at the sliding window start position has been transmitted a maximum number of time is performed, and in response a different data unit is positioned at the sliding window start position.