Flows Reduction Scheme Using Two MPLS Tags in Software-Defined Network

This paper proposes a scheme to reduce the number of flow entries permanently stored in an OpenFlow switch and the number of configuration messages from a controller in a software-defined network (SDN). In an SDN, a flow table in an OpenFlow switch is used to instruct packets. The flow table consists of flow entries decided by the controller. A flow request is sent from the OpenFlow switch to the controller if the incoming packet does not match any flow entry in the flow table. The controller's central processing unit may be overloaded to handle user requests, since the user requests for different data types have been rapidly increasing. As a result, flow configuration in switches is delayed. Moreover, the control plane may be flooded by configuration messages of those requests. A scheme to permanently keep the flow entries in the switch can reduce the number of requests. However, a large number of permanent flow entries is required. Other switch features may be degraded, since there is not enough memory in the flow table to implement those features. In the proposed scheme, switches in the network are divided into multiple regions. In order to guide packets from sources to destinations, the flow table incorporating the concept of two multiprotocol label switching tags is re-designed. One tag directs a packet from a source switch to an edge switch in the destination region. The other tag directs the packet from that edge switch to another switch in the same region. A mathematical model for the proposed scheme is formulated as an integer linear programming to determine a set of switches in each region so that the total number of permanent flow entries in the network can be minimized. The performance of the proposed scheme is analyzed. Moreover, the proposed scheme is implemented and demonstrated via Japanese Science Information Network 5.