If the optical lines to either OLT are disabled, then the other OLT can provide an alternate connection until {HEAD ~ the optical line} to {TAIL ~ the other OLT} is restored 
to
If the optical lines to either OLT are disabled , then the other OLT can provide an alternate connection until { HEAD ~ the optical line } to { TAIL ~ the other OLT } is restored
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH