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