title: TCP's Welcome port vs connection port and the purpose of three way handshake
body: <p>This is the picture from the textbook James F. Kurose, Keith W. Ross: <em>Computer networking: a top-down approach,</em> ISBN-13: 978-0-13-285620-1. ISBN-10: 0-13-285620-4.</p>
  
  <p><a href="https://i.stack.imgur.com/DwMk0.png" rel="noreferrer"><img src="https://i.stack.imgur.com/DwMk0.png" alt="enter image description here"></a></p>
  
  <p>According to the picture, the welcoming port is different to actual connection port.(since different socket is assigned a different port number.
  So let's say Client is initializing a HTTP request, so the welcoming port is 80 on the web server, and then the actual connection port is different than 80?</p>
  
  <p>The second question is, what's the purpose of handshaking for TCP? I was only taught that why TCP's handshaking is but don't actually know why handshaking is essential. If we get rid of handshaking from TCP, we can still make TCP a reliable data transfer protocol, can't we?</p>