Embedding Delay-Constrained VNF Forwarding Graphs into Reconfigurable WDM Optical Networks

Operators of reconfigurable wavelength-division-multiplexed (WDM) optical networks adapt the lightpath topology to balance load and reduce transmission delays. Such an adaption generally depends on a known or estimated traffic matrix. Network-function virtualization allows to implicitly change this traffic matrix. However, these two degrees of freedom have largely been considered separately, using resources suboptimally. Especially for delay-sensitive services, an optimal use of resources can be crucial. We jointly optimize the embedding of virtualized-network-function (VNF) forwarding graphs with delay constraints and the lightpath topology of WDM optical networks. Unlike previous work, we consider all three types of delays: propagation, processing and forwarding-induced queuing delay and model the latter two as M/M/1 queues. We approximate our exact mixed-integer nonlinear program formulation by a mixed-integer linear program and evaluate our approach for small-scale examples of a multicast service.