The adapter also monitors {HEAD ~ the tone cadences} returned to {TAIL ~ the calling party} on the DID trunk or E&M tie line to determine if the called extension is busy or ringing  
The adapter also monitors { HEAD ~ the tone cadences } returned to { TAIL ~ the calling party } on the DID trunk or E&M tie line to determine if the called extension is busy or ringing
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH