The thesis describes the concept of software-defined networking, OpenFlow protocol and architecture of software-defined network. The emphasis is on separation of network logic and physical devices, thus achieving centralization of network management. The entire network is controlled from a single software program (controller). The network elements (switches) are handled with a standardized OpenFlow protocol. Three models of SDN implementation in the network are described (network virtualization, evolutionary approach and centralized management) along with concept of network functions virtualization. Fourth generation networks (4G) are in wide use nowadays. User equipment remains the same as mobile equipment in UMTS and GSM networks, but the biggest changes are being introduced in radio access network. Access network is reduced to one entity (eNodeB) with four interfaces. Core network is using "all IP" architecture and the most important node in the network is MME, responsible for signaling between user and core network. Demand for mobile traffic is growing, and requests for services are becoming more diverse. So next step is SDN introduction in mobile networks. Main challenge is to introduce changes in the radio access network. Possible implementations of SDN in mobile networks are described, as well as several integration solutions, with their pros and cons. Practical part of thesis shows possible methodology for performance testing of switches and controllers (POX and OpenFlow Reference), in Mininet environment. Processing speed of flow modification message was examined, along with speed of adding new flows, detection time of error message, and transfer parameters of TCP and UDP traffic (bandwidth links, delay, loss,transmitted traffic) with Iperf tool. Cbench tool was used to test controller's maximum bandwidth (concerning flow modification messages).