A Collision Problem in OSI Standard Formal Specifications

A collision problem is presented which can occur between two adjacent protocol entities, a user and its local provider. We consider synchronous and asynchronous communication mechanisms at the Service Access Point between the entities; this is normally an implementation choice. It is shown that even if the problem is limited by using a synchronous communication mechanism, instead of an asynchronous one, it still occurs. We suggest that whenever this case is found, the service provided by the protocol entity must be interpreted differently by its user, ignoring some primitives. When an asynchronous communication mechanism is used, care must be taken to verify that those primitives to be ignored cannot be misinterpreted as new primitives; finally, we point out that the protocol specification could be redesigned to handle these collision cases