title: Http persistent connections limit
body: <pre><code>Clients that use persistent connections SHOULD limit the number of simultaneous
  connections that they maintain to a given server. A single-user client SHOULD 
  NOT maintain more than 2 connections with any server or proxy.
  
  [..]
  </code></pre>
  
  <p>I'm particularly uncertain about the "SHOULD"..what's the sense of it?anw Why?</p>
  
  <p>I know that HTTP persistent connections, also called HTTP keep-alive,are the idea of using the same TCP connection to send and receive multiple HTTP requests/responses, as opposed to opening a new one for every single request/response pair. I know that Using persistent connections is very important for improving HTTP performance.</p>
  
  <ul>
  <li>Is the 2 connections-limit per server predefined or not?</li>
  <li>When is a request going to use an existing connection or fetching a new one?</li>
  </ul>
  
  <p>let's say I have an HTML page containing the following image references:</p>
  
  <pre><code>&lt;img src="http://example.com/image1.gif"/&gt;
  &lt;img src="http://example.com/image2.gif"/&gt;
  &lt;img src="http://example.com/image3.gif"/&gt;
  &lt;img src="http://example.com/image4.gif"/&gt;
  </code></pre>
  
  <p>My server's keep-alive directive is turned on:what is happening here in terms persistent connections??The optimizing rule/trick related to the 2 simultaneous-connections-per-server limit like the one following is valid?</p>
  
  <pre><code>&lt;img src="http://example.com/image1.gif"/&gt;
  &lt;img src="http://example.com/image2.gif"/&gt;
  &lt;img src="http://example2.com/image3.gif"/&gt;
  &lt;img src="http://example2.com/image4.gif"/&gt;
  </code></pre>
  
  <p>thanks </p>