primarily testing bi directional communicative connectivity, via {HEAD ~ the LAN}, between a primary and a backup redundant network access point of the set of {TAIL ~ network access points} 
primarily testing bi directional communicative connectivity , via { HEAD ~ the LAN } , between a primary and a backup redundant network access point of the set of { TAIL ~ network access points }
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 OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL