On {HEAD ~ basis} of the distribution graph, the shortest paths from {TAIL ~ the distribution node} to each of the other nodes are calculated 
On { HEAD ~ basis } of the distribution graph , the shortest paths from { TAIL ~ the distribution node } to each of the other nodes are calculated
OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH