Multi-Tree Multicast Traffic Engineering for Software-Defined Networks.

Although Software-Defined Networking (SDN) enables flexible network resource allocations for traffic engi neering, current literature mostly focuses on unicast communications. Compared to traffic engineering for multiple unicast flows, multicast traffic engineering for multiple trees is very challenging not only because minimizing the bandwidth consumption of a single multicast tree by solving the Steine r tree problem is already NP-Hard, but the Steiner tree problem doe not considered the link capacity constraint for multicast flows and node capacity constraint to store the forwarding entries in Group Table of OpenFlow. In this paper, therefore, we first study the hardness results of scalable multicast tra ffic engineering in SDN. We prove that scalable multicast traffic engineering with only the node capacity constraint is NP-Ha rd and not approximable within δ, which is the number of destinations in the largest multicast group. We then prove that scal able multicast traffic engineering with both the node and link capacity constraints is NP-Hard and not approximable within any ratio. To solve the problem, we design aδ-approximation algorithm, named Multi-Tree Routing and State Assignment Algorithm (MTRSA), for the first case and extend to the general multicast traffic engineering problem. The simulat ion results demonstrate that the solutions obtained by the prop osed algorithm are more bandwidth-efficient and scalable than the shortest-path trees and Steiner trees. Most importantl y, MTRSA is computation-efficient and can be deployed in SDN since it can generate the solution on massive networks in a short time.