These data requiring {HEAD ~ storage} are stored in a storage device installed in {TAIL ~ the optical network unit} 
These data requiring { HEAD ~ storage } are stored in a storage device installed in { TAIL ~ the optical network unit }
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL