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