title: Network disconnect issue when iOS screen locks
body: <p>In iOS 5  When Application Enter background wi-fi connection is lost.</p>
  
  <p>But I want to use wi-fi connection for the next 4-5 minutes before the device sleeps as some tasks can be performed within 4-5 minutes of application enter background.</p>
  
  <p>I think this can be accomplished by using <code>beginBackgroundTaskWithExpirationHandler:</code>, but i am not able to solve the problem</p>