{HEAD ~ The controller} sends {TAIL ~ a notification} to the agent when the file updates are retrieved, and the agent retrieves the file updates from the controller 
sends
{ HEAD ~ The controller } sends { TAIL ~ a notification } to the agent when the file updates are retrieved , and the agent retrieves the file updates from the controller
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH