the network cost for operating {HEAD ~ the modified network topology} is greater than or equal to the network cost for operating {TAIL ~ the current network topology} 
the network cost for operating { HEAD ~ the modified network topology } is greater than or equal to the network cost for operating { TAIL ~ the current network topology }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL