title: Why tcp termination need 4-way-handshake?
body: <p>When connection sets up, there is:</p>
  <blockquote>
  <p>Client ------SYN-----&gt; Server</p>
  <p>Client &lt;---ACK/SYN---- Server        ----①</p>
  <p>Client ------ACK-----&gt; Server</p>
  </blockquote>
  <p>and when termination comes, there is:</p>
  <blockquote>
  <p>Client ------FIN-----&gt; Server</p>
  <p>Client &lt;-----ACK------ Server        ----②</p>
  <p>Client &lt;-----FIN------ Server        ----③</p>
  <p>Client ------ACK-----&gt; Server</p>
  </blockquote>
  <p>my question is why ② and ③ can not set in the same package like ① which is ACK and SYN set in one package ???</p>