First let's try writing some **UDP** C program under [Unix](unix.md). Remember that UDP is the unreliable protocol, so it's possible our messages may get lost or distorted, but in programs that can handle some losses this is the faster and more KISS way. Our program will be peer-to-peer, it will create two sockets, one listening and one sending. It will make a few message exchange turns, in each turn it will send something to its partner, it will check if it itself got any message and then will wait for some time before the next round. Note that we will use a non-blocking receiving socket, i.e. checking if we have any messages won't pause our program if there is nothing to be received, we'll simply move on if there is nothing (that's how realtime games may do it, but other kinds of server may rather a use blocking socket if they intend to do nothing while waiting for a message). Also pay attention to the fact that the program will choose its port number based on a one letter "name" we give to the program -- this is so that if we test the programs on the same computer (where both will have the same IP address), they will choose different ports (different processes on the same computer cannot of course use the same port).