故障探测(failure detector)

failure detectors是不可靠的，原因是crash server很难与 slow server区分。

Strong accuracy: no process is suspected before it crashes

Weak accuracy: some correct process is never suspected

Eventual Strong accuracy: there is a time after which correct processes are not suspected by any correct process

Eventual Weak accuracy: there is a time after which some correct process is never suspected by any correct process