{HEAD ~ Arbiter} 16 receives {TAIL ~ requests} for access from any of a number of requesters 
{ HEAD ~ Arbiter } 16 receives { TAIL ~ requests } for access from any of a number of requesters
HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH