There is almost always more than one incoming DID trunk or {HEAD ~ E&M tie line} into {TAIL ~ a PBX} 
There is almost always more than one incoming DID trunk or { HEAD ~ E&M tie line } into { TAIL ~ a PBX }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL