Each set of resources is allocated only for {HEAD ~ the period} of {TAIL ~ time} needed to perform the required function 
of
Each set of resources is allocated only for { HEAD ~ the period } of { TAIL ~ time } needed to perform the required function
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 OTH