This 64-bit counter tallies packets that were prevented from being delivered to the Higher Layer because of a resource limitation (such as an input buffer or queue running out of room), counted over the current, still-running 15-minute window. Unlike the ring-side error counters, this one points at the local router itself being unable to keep up — the frames arrived intact off the ring but the router's own CPU/ASIC couldn't accept them — so a rising count here is a load/capacity problem on this box, not a ring or cabling issue. A sustained rise in this counter during a traffic surge, with no corresponding rise in any ring-side error counter, would point to this router's own buffering running out rather than to anything wrong with the ring itself.