title: How does a system's TCP/IP stack differentiate between multiple programs connecting to the same address and port?
body: <p>Suppose two web browsers are running on the same computer and are accessing the same website (in other words, accessing the same IP address on the same port).  </p>
  
  <p>How does the operating system recognize which packets are from/for which program?</p>
  
  <p>Does each program have a unique id field in the TCP header? If so, what is the field called?</p>