This counter counts the number of times the switch sent a group-specific query to hosts and did not receive a membership report back within the expected reply window, so it assumes no host still wants that group. On this element this is the normal mechanism by which stale multicast groups get aged out and pruned from the forwarding table when no explicit leave was sent, so a moderate steady count is expected behavior rather than necessarily a fault. For instance, if a set-top box is unplugged without sending a leave, this counter increments once when its group's next query goes unanswered, and the switch then stops forwarding that stream to the port.