This read-only counter counts cells arriving on the DS3 interface that were discarded because their header matched the pattern reserved for IMA control cells, meaning they were filtered out rather than passed as user data. Admins use this to understand how many cells are being intercepted as IMA control traffic versus actual payload, which is relevant when the DS3 port is carrying an IMA-related trunk. For example, an unexpectedly high value here on a port not expected to carry IMA control traffic could indicate cells are being misclassified.