In addition, {HEAD ~ links} can be added to {TAIL ~ the network topology model} to reduce the cost of network operation 
In addition , { HEAD ~ links } can be added to { TAIL ~ the network topology model } to reduce the cost of network operation
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH