Component Based Development (CBD) aims to facilitate the construction of large-scale applications by supporting the composition of simple building blocks into complex applications. Components specification is thus needed to ensure the safety of composing systems from components. This paper focus on component protocols specification and provides a framework for modelling protocols together with their composition. We start by investigating compatibility of component protocols based on service observation. Two compatibility relations together with their characterisation by the preservation to their degree of change property are proposed. Safety and liveness properties such as deadlock-freeness and proper termination of protocols are preserved up to different extents. Then, we propose some behavioural subtyping relations for component protocols related to the principle of substitutability. Finally, we address the soundness of our subtyping relations by showing the existing link between compatibility and substitutability concepts, namely their combination, which have found necessary when dealing with incremental design of components.