This is a running counter: total number of service requests for the mobile node denied by the home agent (sum of all registrations denied with Code 128 through Code 159). Since Mobile IP counters like this only increment and never reset on their own, an admin polls it periodically and watches the rate of change rather than the absolute value — a counter that suddenly climbs fast points at a specific failure mode (e.g. bad authentication, a misconfigured agent, or a flapping mobile node) tied to this exact event.