This read-only Counter32 counts RSIP (Restart In Progress) messages sent to the call agent for which a failure return code was received or which timed out waiting for a response. An admin cares because a failed restart notification means the call agent may not be aware the gateway or endpoint restarted, risking it continuing to route calls to an endpoint that is not yet ready. For example, an operator seeing calls routed to an endpoint that just reset and failed would check whether this counter shows the RSIP notification itself failed to be acknowledged.