Description: NTP Reference Clock Identifier.  This is a
32 bit code identifying the particular reference
clock.  In the case of stratum 0 (unspecified) or
stratum 1 (primary reference), this is a four-
octet, left-justified, zero-padded ASCII string.
While not enumerated as part of the NTP spec, the
following are suggested ASCII identifiers:
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DCN             DCN routing protocol
NIST            NIST public modem
TSP             TSP time protocol
DTS             Digital Time Service
ATOM            Atomic clock (calibrated)
VLF             VLF radio (OMEGA,etc.)
callsign        Generic radio
LORC            LORAN-C radionavigation
GOES            GOES UHF environment satellite
GPS             GPS UHF satellite positioning
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The following ref ids are used by the SyncServer:
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GPS             GPS satellite)
IRIG            IRIG B timecode
1PPS            Ext. 1 PPS input
E10M              Ext. 10 MHz input
FREE            Internal Clock
FLY             Internal Clock after the Hardware
                Clock reference is lost
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