A SIM server provides access to the SIMs, a SIM librarian catalogs the SIMs, and {HEAD ~ a SIM accounting system} tracks {TAIL ~ and/bills} for SIM usage 
tracks
A SIM server provides access to the SIMs , a SIM librarian catalogs the SIMs , and { HEAD ~ a SIM accounting system } tracks { TAIL ~ and / bills } for SIM usage
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH