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