The apparatus includes {HEAD ~ each timing server} of the multiple pluralities of {TAIL ~ timing servers} configured to transmit, receive, and monitor synchronization signals 
The apparatus includes { HEAD ~ each timing server } of the multiple pluralities of { TAIL ~ timing servers } configured to transmit , receive , and monitor synchronization signals
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH