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