The Application Layer
The network is the essential piece that they all have in common. This applies to all infrastructure (Layers 1, 2, and 3) as well as supplemental services that might be shared additionally.
Campus, data center, branch, WAN/MAN, enterprise edge, teleworker
This is a rather subjective answer as it calls upon the reader to reference a solution from his or her own experiences. To a large degree, the solution will be based on personal networking experiences. A sample solution would include