You know (one of) the main difference(s) between TCP and UDP, don't you? TCP is connection-oriented, UDP isn't. So there is no UDP core-functionality to check whether the receiver is alive (/has the port opened). You'd either need to create server-side code or know the server-behavior (e.g. responses to specific datagrams) to achieve an UDP port-scanner. If you're able to write server-side code the best is to ask for UDP port status via TCP since it has reliable data-transfer implemented.