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