A promising development in the design of datacenters is the hybrid network architecture consisting of both optical and electrical elements, in which end-to-end traffic can be routed through either an electrical path or an optical path. The core optical switch is used to dynamically create optical paths between pairs of electrical edge-switches in such a datacenter network. In this context, the joint problem of bandwidth allocation and VM-placement poses new and different challenges not addressed yet in hybrid datacenter. In particular, we foresee two issues: (i) the number of edge-switches that can be simultaneously reached using optical paths from an edge-switch is limited by the size of the optical switch, (ii) the dynamic creation of optical paths can potentially establish a constrained optical network topology leading to poor performance. In this work, we abstract the requests of tenants as virtual networks, and study the problem of embedding virtual networks on a hybrid datacenter. We formulate the problem as a non-linear optimization problem and analyze its complexity. We develop and analyse three algorithms for embedding dynamically arriving virtual network demands on a hybrid optical–electrical datacenter. Through simulations, we demonstrate the effectiveness of not only exploiting the already established optical paths, but also of using electrical network in embedding requests of virtual networks. 
Dynamic resource allocation in hybrid optical–electrical datacenter networks