{TAIL ~ The controller} sends the file update information to the agent, and the agent requests {HEAD ~ the controller} to retrieve file updates 
{ TAIL ~ The controller } sends the file update information to the agent , and the agent requests { HEAD ~ the controller } to retrieve file updates
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH