Democratic Resolution of Resource Conflicts Between SDN Control Programs

Resource conflicts are inevitable on any shared infrastructure. In Software-Defined Networks (SDNs), different controller modules with diverse objectives may be installed on the SDN controller. Each module independently generates resource requests that may conflict with the objectives of a different module. For example, a controller module for maintaining high availability may want resource allocations that require too much core network bandwidth and thus conflict with another module that aims to minimize core bandwidth usage. In such a situation, it is imperative to identify and install resource allocations that achieve network wide global objectives that may not be known to individual modules, e.g., high availability with acceptable bandwidth usage. This problem has received only limited attention, with most prior work focused on detecting, avoiding, and resolving rule-level conflicts in the context of OpenFlow. In this paper, we present an automatic resolution mechanism based on a family of voting procedures, and apply it to resolve resource conflicts among SDN and cloud controller programs. We observe that the choice of appropriate resolution mechanism depends on two properties of the deployed modules: their precision and parity. Based on these properties, a network operator can apply a range of resolution techniques. We present two such techniques. Overall, our system promotes modularity and does not require each controller module to divulge its objectives or algorithms to other modules. We demonstrate the improvement in allocation quality over various alternative resolution methods, such as static priorities or equal weight, round-robin decisions. Finally, we provide a qualitative comparison of this work to recent methods based on utility or currency.