Unable to pause NSBundleResourceRequest

I'm downloading resources from Itunes, using NSBundleResourceRequest.

The following code is using to pause the progress.

var request = NSBundleResourceRequest(tags: [tags])

self.request.beginAccessingResources { error in

  if let error = error {
    onFailure(error)
  } else {
    onSuccess()
  }
} 

 @IBAction func buttonPauseAction() {
          self.request.progress.pause()
  }

But download is not getting paused.

Please help me on this, why I'm not able to pause. any reason for this

Thanks in advance.