This read-only counter tracks the number of times the AUSM card attempted to transmit a cell but was blocked because its hardware Transmit FIFO was already full, and notably it counts transmit attempts blocked, not cells actually dropped. An administrator uses it as a per-card indicator of transmit-side hardware saturation, and can also find the same value duplicated in the per-channel counter group for finer-grained monitoring. Because it does not directly equal dropped cells, an operator should still consult the discard-specific counters to quantify actual traffic loss.