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