Thus {HEAD ~ high priority services} can pre empt {TAIL ~ the usage} of wireless resources by low priority services 
pre empt
Thus { HEAD ~ high priority services } can pre empt { TAIL ~ the usage } of wireless resources by low priority services
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH