Traditional network architecture is inflexible and complex. This observation has led to a paradigm shift toward software-defined networks (SDNs), in which the network control level is separated from the data link layer. This change became possible because of the control plane transfer from switching equipment to software modules that run on a dedicated server called a controller (or a network operating system) or to network applications that work with this controller. Methods of presentation, storage, and communication interfaces with network topology elements available to SDN controller users are the most important aspects of network operating systems because the operation of some key controller modules depends heavily on the internal representation of the network topology. Firewall and routing modules can be cited as examples of these modules. This paper considers the methods used to represent and store the network topology, as well as communication interfaces with corresponding modules of the Floodlight controller. An alternative algorithm for exchanging messages on the changes in the network topology between the controller and network applications has been proposed and developed. The algorithm makes it possible to issue notifications based on a subscription to relevant events. An API for the module of interacting with applied programs of the SDN controller has been developed. The Topology Tracker module has been designed based on this algorithm and API. In active mode, this module can inform network applications about the changes in the network topology and store its compact representation for the interaction acceleration.