This read-only counter, explicitly documented as a per-card (not per-channel) statistic despite appearing in the channel table, counts the number of times the AUSM card attempted to send a cell but couldn't because its hardware transmit FIFO was already full, and the description specifically clarifies this is not the same as a count of cells actually dropped. Admins use this as a hardware-level indicator of transmit-side buffering pressure on the whole card, distinct from any per-channel discard statistics, useful for diagnosing card-level performance bottlenecks rather than individual connection problems. For example, a rising chanTxFifoFullCnt across an entire card, even when individual channels show low discard counts, would point the admin toward a card-wide hardware transmit-capacity issue rather than a single misbehaving connection.