The re-transmission of transmission units (TUs) received in a communication device over a communication link is controlled to improve the information carrying capacity of the link. A received TU has an associated service characteristic indicative of a quality of service (QOS) for the TU. The service characteristic is associated with a select set of key performance indicators (KPIs), such as measures of packet error, packet delay, packet delay variation, and/or packet loss experienced by TUs on the communication link. Upon receipt of a TU, the performance of the communication link is evaluated with respect to each KPI in the select set to obtain a corresponding measurement value, and the measurement values are compared to corresponding threshold values. Upon determining that a determined performance value does not satisfy a corresponding threshold value for a KPI in the select set, re-transmission of the TU is requested.