  We consider a reaction--diffusion equation in a domain consisting of two bulk
regions connected via small channels periodically distributed within a thin
layer. The height and the thickness of the channels are of order $\epsilon$,
and the equation inside the layer depends on the parameter $\epsilon$ and an
additional parameter $\gamma \in [-1,1)$, which describes the size of the
diffusion in the layer. We derive effective models for the limit $\epsilon \to
0 $, when the channel-domain is replaced by an interface between the two
bulk-domains.
