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