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