In Siemens TIA Portal, the 'Open user communication' is useful to establish a TCP or ISO-on-TCP or UDP communication connection with other devices (other than S7 devices also). The instructions 'TSEND_C' and 'TRCV_C' are used to establish the connections, managing the data and verification of received data.
Part 2 : https://youtu.be/TPp1FEtATNY