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