title: why to use classes inside namespace
body: <p>I wish to know the actual reason behind writing the class names inside namespace. What purpose do they solve? Do they include the classes or do something else? Any help is greatly appreciated.</p>
  
  <pre><code>namespace ns3 { 
  class Channel;
  class SpectrumChannel;
  class MyMod;                        ;
  
  class NewModule : public NetDevice
  {   
  public:
  // methods and data
  }
  </code></pre>