Different types of entities (such as hardware, transport facilities, and subscriber service) have a variety of state characteristics that express the availability of their underlying resources that are specific to each entity type. However, a state model is expected to be common to a large number of types of entities. It expresses key aspects of their availability at any given time. The purpose of the state model is to indicate the availability of an entity in providing its functions and, if an entity is not available, to indicate the cause of the unavailability and what kind of activity may be taken by the manager (e.g., the OS or the craft) to make the entity available.