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