distributed-algorithm

I understand that failure detectors in asynchronous systems are basically classified as (eventually)perfect/(eventually)strong and how those classes are defined, but I kind of struggle to get the intuition behind it. Suppose I have a concrete implementation of a failure detector, which periodically listens for heartbeat messages from each process. If a process hasn't sent its heartbeat message for a while, the process will be added to a list of suspects until a message is received from the process. Now, how do I know which class is this implementation of an FD? Would that require a formal