title: UDP payload length and packet transmission
body: <p>I have data 1245 MB for trasmission via UDP over IPv4. 
  For calculation of expected number of packet transmission from A to B then B relay to C, if the data transmitted in blocks of size 320bytes (i.e; payload = 320bytes), and header is 20 bytes, do we minus 20 from 320 or add in?</p>
  
  <pre><code>For instance, 
  1245MB = 1305477120 bytes
  Total UDP Payload = 320 - 20 or 320 + 20?
  </code></pre>