Optionally, each access controller includes {HEAD ~ two ATM interfaces} 710 to provide {TAIL ~ network access redundancy} 
to provide
Optionally , each access controller includes { HEAD ~ two ATM interfaces } 710 to provide { TAIL ~ network access redundancy }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL