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