This paper generalizes a specification technique based on input/output relations on streams to describe mobile systems. We consider networks of components communicating asynchronously via unbounded directed channels. Mobility is achieved by allowing the components to communicate channel ports. We distinguish between many-to-many and two variants of point-to-point communication. The communication paradigms are semantically under-pinned by denotational models. The models are formulated in the context of timed nondeterministic data-flow networks and presented in a step-wise fashion. The emphasis is on capturing the special kind of dynamic hiding characterizing mobile systems. We demonstrate the proposed approach in a number of small examples.
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