Formal Methods in Communication Protocol Design

ion and Stepwise Refinement The specifications described above must embody the key concept of Abstraction if they are to be successful. To be abstract, a specification must include the essential requirements that an object must satisfy and omit the unessential. A service specification is abstract primarily in the sense that it a specification must include the essential requirements that an object must satisfy and omit the unessential. A service specification is abstract primarily in the sense that it does not describe how the service is achieved (i.e., the interactions among its constituent entities), and secondarily in the sense that it defines only the general form of the interaction with its users (not the specific interface). A protocol specification is a refinement or distributed “implementation” of its service specification in the sense that it partly defines how the service is provided (i.e., by a set of cooperating entities). This “implementation” of the service is what is usually meant by the design of a protocol layer. The protocol specification should define each entity to the degree necessary to ensure compatability with the other entities of the layer, but no further. Each entity remains to be implemented in the more conventional sense of that term, typically by coding in a particular programming language. There may be several steps in this process until the lowest level implementation of a given protocol layer is achieved