In this paper, we present a new and optimistic approach to the definition of component protocols compatibility, and we provide a framework for modeling component protocols together with their composition. This framework is discussed in terms of compatibility and substitutability checks of protocols. According to the optimistic approach, two protocols are compatible if they are composable and their composition leads to a usable protocol, that is a protocol such that there exists an environment ensuring safety and liveness property of the composed protocol, which is obtained by the composition of the involved protocol and that environment. Safety and liveness properties such as deadlock-freeness and proper termination of protocols are considered up to different extents. Based on that, we present two protocols compatibility relations related to the usability concept, together with two behavioural subtyping relations related to the principle of substitutability. We address their soundness by showing the existing link between compatibility and substitutability relations, which have found necessary when dealing with incremental design of protocols.