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