If a change to line switching data transfer is to take {TAIL ~ place}, then a line to another switch is switched through {HEAD ~ the exchange} 4 and the data are transferred to this by line switching 
If a change to line switching data transfer is to take { TAIL ~ place } , then a line to another switch is switched through { HEAD ~ the exchange } 4 and the data are transferred to this by line switching
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH