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