{TAIL ~ A p code frame} or simply frame represents {HEAD ~ a unit} of action or operation in the system 
{ TAIL ~ A p code frame } or simply frame represents { HEAD ~ a unit } of action or operation in the system
TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH