The Software-defined network (SDN) uses a centralized SDN controller to store flow entries in the flow table of each SDN switch; the entries in the switch control packet flows. When a multicast service is provided in an SDN, the SDN controller stores a multicast entry dedicated for a multicast group in each SDN switch. Due to the limited capacity of each flow table, the number of flow entries required to set up a multicast tree must be suppressed. A conventional multicast routing scheme suppresses the number of multicast entries in one multicast tree by replacing some of them with unicast entries. However, since the conventional scheme individually determines a multicast tree for each request, unicast entries dedicated to the same receiver are distributed to various SDN switches if there are multiple multicast service requests. Therefore, further reduction in the number of flow entries is still possible. In this paper, we propose a multicast routing model for multiple multicast requests that minimizes the number of flow entries. This model determines multiple multicast trees simultaneously so that a unicast entry dedicated to the same receiver and stored in the same SDN switch is shared by multicast trees. We formulate the proposed model as an integer linear programming (ILP) problem. In addition, we develop a heuristic algorithm which can be used when the ILP problem cannot be solved in practical time. Numerical results show that the proposed model reduces the required number of flow entries compared to two benchmark models; the maximum reduction ratio is 49.3% when the number of multicast requests is 40.

In recent years, software-defined networking (SDN), which performs centralized network management with software, has attracted much attention. Although packets are transmitted based on flow entries in SDN switches, the number of flow entries that the SDN switches can handle is limited. To overcome this difficulty, this paper proposes a flow-based routing method that performs flexible routing control with a small number of flow entries. The proposed method provides mixed integer programming. It assigns common paths to flows that can be aggregated at intermediate switches, while considering the utilization of network links. Because it is difficult for mixed integer programming to compute large-scale problems, the proposed method also provides a heuristic algorithm for them. Through numerical experiments, this paper shows that the proposed method efficiently reduces both the number of flow entries and the loads of congested links.