title: one port for multiple applications [network]
body: <p>Let say I have two processes, both are listening on the port 80 (html) awaiting for an html packet to be unpacked, analyzed and displayed.
  Now how does the system know which process is the html packet for ?
  For instance, It seems Skype is listening on the port 80 while another application does too. How does Skype know "this packet is for me ?" and on which network layer that process is happening ?</p>