The SA is responsible for responding to requests from {HEAD ~ the DA} of {TAIL ~ another subsystem} 
of
The SA is responsible for responding to requests from { HEAD ~ the DA } of { TAIL ~ another subsystem }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL