Complex sentence: As it implements a software architecture for distributed computing, it therefore also implements a special variant of the more general client-server model, wherein, in general, any application using ESB can behave as server or client in turns.
Split into simpler sentences: As it implements a software architecture for distributed computing, it therefore also implements a special variant of the more general client-server model. Whereas in general any application using ESB can behave as server or client in turns.