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