Optimal Service Function Tree Embedding for NFV Enabled Multicast

In network traffic engineering, multicast is designed to deliver the same content from a single source to a group of destinations. Recently, NFV enabled multicast has been developed by deploying virtual network functions (VNFs) over the target network. To fulfill the multicast task with a service function chain (SFC) requirement, a service function tree (SFT) embedded in the shared multicast tree has to be built. Given the huge space of SFT embedding solutions, however, it is extremely hard to find the optimal one such that the total traffic delivery cost is minimized. In this paper, we tackle the optimal SFT embedding problem in NFV enabled multicast task. Specifically, we formally define the problem and formulate it with an integer linear programming (ILP), which turns out to be NP-hard. Then, a two-stage algorithm is proposed to deal with the problem with an approximation ratio of 1 + rho, where rho is the best approximation ratio of Steiner tree and can be as small as 1.39. With extensive experimental evaluations, we demonstrate that by applying our SFT embedding solution, the cost saving of multicast traffic delivery can be up to 22.41%, compared with the random SFT embedding strategy.