of these issues providing a high degree of code reuse the spd framework has two aspects the first is the framework itself which provides all design and implementation patterns for the tests and the second is helper utilities which create a general interface to common resources such as adapter use protocol use aix resources use etc fig1 is a schematic block diagram illustrating a hierarchy 330 of classes used in the spd architecture in accordance with a preferred embodiment of the present invention the classes shown in the figure are described hereinbelow this class is an orchestrator of all spd frameworks it decides which models to run and when handles interactions with spd including registering callbacks and providing handler functions it creates event objects from received packets or requests and invokes event processing it also supplies an interface for model test termination this class provide a general interface to an algorithm by which the model on the node is initialized or terminated on every node type this algorithm is different and this class hides specifics of the algorithm two derived classes u2014 primaryalgorithm 340 and nonprimaryalgorithm 342 implement their logic in the proper way this class represents model finite state machine fsm is responsible for state transitions and holds state objects of the fsm states users derive their own classes from this class representing different models of behavior on different types of nodes this class provides an interface for creating and enumerating test models its derived class holds knowledge of existing test specific models this class represents the state of.