One virtual backplane system includes a bus, and {HEAD ~ first and second line cards} coupled to {TAIL ~ the bus} 
coupled to
One virtual backplane system includes a bus , and { HEAD ~ first and second line cards } coupled to { TAIL ~ the bus }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL