udp.begin(1234);   // start UDP on port 1234
    udp.beginPacket(IPAddress(127, 0, 0, 1), 56);  // start a packet sending to IP 127.0.0.1 on port 56.
    udp.write(0);  // write a byte of value 0 to the packet
    udp.endPacket();  // actually send the packet.