The MAB RTU control system developed by Infoware Zrt., is a control engineering system which is used to supervise and control electrical energy systems remotly. The main part of the system is the communication unit (gateway), which collects all the information from the field devices, and it's main purpose to build and manage a database for the upper layers. The bay units use different kinds of physical interfaces, and different kinds of protocols to send their data. In the gateway unit, the communication module has a significant importance, it's purpose to receive data and pass it to the main module. The newly designed communication module can receive and send data on four separated lines. It also has an Ethernet port which connects to the systems bus. These new features make this module more powerful than its previous version. My task through my thesis was to implement the network communication using the LWIP stack. The first step of the development was to set up the Ethernet interface. After the configuration of the physical transceiver, and correction of the hardware design mistakes, I was able to receive Ethernet packets with interrupt. The next step was to initialize the LWIP stack and create the network interface, which creates the connection between the microcontroller and the TCP/IP stack. All data that come from the serial ports, are then transmitted to the gateway on a TCP connection, which realize a reliable transmission. The communication module is in a server role, from the view of the connection. To check the parameters of the module, actual state and to make the required changes, I created a website. At the end of my thesis, I present measurement data about the transfer speed of the module and I interpret the conclusion.