The uDPSend block sends to the local port 10002. The uDPReceive block starts a background process that listens at port 10002. Consequently, the uDPReceive block receives what the uDPSend block sends.
Note: There is no causality between the uDPSend block and the uDPReceive block. Therefore the execution order of the blocks is not determined. Additionally, the uDPReceive block starts an own receiving thread, so that the time the data was received is not equal to the time the external function within the uDPReceive block was called. This indeterminism may also show up in the plots.
This example sends data to address 127.0.0.1, which is a special-purpose IPv4 address and is called the localhost or loopback address. When you have to transfer data to another computer you have to use in uDPSend that computer's IP. You've also to set the port number of the remote computer you want to send to.
When you want to receive data from another computer, you have set in uDPReceive the actual port number of the local computer you a willing to receive data to.