This counter tracks the number of data PDU transmission failures for this SU where excessive retries in contention data slots still never received acknowledgment, resulting in the PDU being dropped outright. Admins treat this counter as evidence of actual data loss, more severe than the retry counter alone, since these PDUs never made it through even after retrying. For example, a nonzero and growing cwdIfSuServiceTxExceeded for an SU that also shows high cwdIfSuServiceTxRetries indicates contention on that upstream channel has become severe enough to cause outright data loss, not just delay.