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