1. A problem determination method suitable for a network that has a plurality of paths and a plurality of network components, at least two of which paths include at least one of the network components in common, said method comprising the steps of: determining whether each path of the plurality of paths is a working path or a failed path; determining a set of suspicious network components, each of which suspicious network component is included in every failed path; determining a set of working network components, each of which working network component is included in at least one working path; and identifying a set of failed network components by analyzing the set of suspicious network components and the set of working network components.