title: How is a connection kept opened at the physical layer level
body: <p>I'm having a difficult time understanding the concept of persisent connection.</p>
  
  <p>If we take as an example the Http protocol using the keep-alive header, after tcp/ip performing the handshake along with the necessary validations, the connection is kept alive for x ms, allowing the user to send multiple requests using the same connection/port. The impact of a persistent connection is clear to me, at least at this level of understanding, overhead is reduced.</p>
  
  <ul>
  <li>However, what I cannot seem to understand is how does this connection
  is kept alive at physical level. Is it at logical or physical level and how ?</li>
  <li>If it is at logical level, the message to be sent will already
  contain the headers with information from the performed handshakes
  and validations so it will skip through the steps involved in finding
  the target physical address and other router related actions on the
  packet including http handshake and so on ?</li>
  <li>While a connection is alive, will there be any control (ping) messages
  sent between source and destination to see if they are still there ?</li>
  </ul>
  
  <p>Regards</p>