Agent will check-in to SapphireIMS based on configured check-in interval. Default being 3 minutes which is minimum supported interval and is configurable under Settings > Agent Configuration. Assuming interval is N and If agent is not reporting for more than Nx2 which is a grace period, we shall mark agent as down. Please note that in some cases technically agent may not be down but unable to reach SapphireIMS server because of network issues or agent is not running/healthy in target machine.
For agentless devices, we periodically do ICMP ping with two retries to each device to check device availability. The default poll interval is 15 min which is configurable. In some networks, if ICMP is disabled, we have means to TCP/UDP handshake to known ports used for data collection to check the availability. If we don’t get response either for ICMP or TCP/UDP, then we make the device as unavailable.