The “cost of survivability” is defined as the ratio of the costs of {HEAD ~ network operation} with and without {TAIL ~ survivability requirements} 
without
The “ cost of survivability ” is defined as the ratio of the costs of { HEAD ~ network operation } with and without { TAIL ~ survivability requirements }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL