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