{HEAD ~ A hierarchical version} including multiple star couplers and selection devices is also disclosed, to handle {TAIL ~ a relatively large number} of stations 
{ HEAD ~ A hierarchical version } including multiple star couplers and selection devices is also disclosed , to handle { TAIL ~ a relatively large number } of stations
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH