Patent US 9,686,209

In a network device, a plurality of first counters for measuring respective fill levels of respective queues are maintained, the queues using respective dedicated areas of a memory and a shared area of a memory. A single second counter for measuring a fill level of a shared area is maintained. When a packet is enqueued, the respective first counter corresponding to the queue is updated, and if any part of the packet is stored in the shared area, the single second counter is updated. When the packet is dequeued, the respective first counter is updated, and if any part of the packet was stored in the shared area, the single second counter is updated.