title: OSI model - What's the presentation and session layer for?
body: <p>So I feel I pretty well understand the application layer, and everything below (and including) the transport layer.</p>
  
  <p>The session and presentation layers, though, I don't fully understand.  I've read the simplistic descriptions in Wikipedia, but it doesn't have an example of why separating out those layers is useful.</p>
  
  <p>So:</p>
  
  <ul>
  <li>What is the session layer?  What does it do, and under what circumstances is it better to have a session layer than simply talk to the transport with your app?</li>
  <li>What is the presentation layer?  (same questions as above)</li>
  </ul>
  
  <p>-Adam</p>