Design For Testability (DFT) is understood as the process of introducing some features into a communication software that facilitate the testing process of protocol implementations. DFT at the implementation level deals with a particular realization on a given platform, whereas DFT at the specification level affects all possible implementations regardless of the implementation process. In this paper, we propose in the first part, a generic framework of design for testability where DFT activity

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... s integrated in the communication software development process. A generic model for testability transformation based on modification of a given specification and testability measurement is explained. In the second part, we address one particular problem of DFT, the problem of analyzing the testability of a given module specified as a finite state machine. Transformations in this paper are not the main objective, but they are used to illustrate how testability can be enhanced by finding an augmentation of the given protocol behavior such that a newly obtained specification is more testable than the original one A measure of testability of a protocol entity is assumed to be based on the shortest length of a test suite needed to achieve guaranteed coverage of certain faults. We consider the FSM model of a protocol machine and propose a classification method based on the formalized notions of controllability and observability.