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