This 64-bit counter tallies frames of 16 octets or less arriving from the router's own higher-layer stack, which the MIB defines as the threshold for a 'short' packet, over the current, still-running 15-minute window. A short frame originating from this box's own higher layer points at a local software or driver bug generating malformed frames before they even reach the ring, which is a different troubleshooting path than a ring-side short packet that came from somewhere else on the fiber. Seeing this counter increment right after a software upgrade on this router, with the ring-side short-packet counter staying flat, would point at the new software generating malformed frames rather than at anything on the ring itself.