  Network virtualization techniques allow for the coexistence of many virtual
networks (VNs) jointly sharing the resources of an underlying substrate
network. The Virtual Network Embedding problem (VNE) arises when looking for
the most profitable set of VNs to embed onto the substrate. In this paper, we
address the offline version of the problem. We propose a Mixed-Integer Linear
Programming formulation to solve it to optimality which accounts for acceptance
and rejection of virtual network requests, allowing for both splittable and
unsplittable (single path) routing schemes. Our formulation also considers a
Rent-at-Bulk (RaB) model for the rental of substrate capacities where economies
of scale apply. To better emphasize the importance of RaB, we also compare our
method to a baseline one which only takes RaB into account a posteriori, once a
solution to VNE, oblivious to RaB, has been found. Computational experiments
show the viability of our approach, stressing the relevance of addressing RaB
directly with an exact formulation
