This is a short overview for the reference clocks currently supported by xntp V3. (Ultimate wisdom can be obtained from xntpd/refclock_*.c this file was derived from that information - unfortunately some comments in the files tend to get stale - so use with caution) Refclock address Type 127.127.0.x no clock (fails to configure) 127.127.1.x local clock - use local clock as reference 127.127.2.x no clock (fails to configure) 127.127.3.x PSTI 1010/1020 WWV Clock 127.127.4.x SPECTRACOM WWVB receiver 8170 and Netclock/2 127.127.5.x Kinimetric Truetime 468-DC GOES receiver 127.127.6.x IRIG audio decode (Sun & modified BSD audio driver) 127.127.7.x CHU Timecode (via normal receiver & Bell 103 modem) 127.127.8.x PARSE (generic driver for a bunch of DCF/GPS clocks can be extended for other clocks too) 8.0-3 Meinberg PZF535/TCXO 8.4-7 Meinberg PZF535/OCXO 8.8-11 Meinberg DCF U/A 31 8.12-15 ELV DCF7000 8.16-19 Walter Schmid DCF receiver (Kit) 8.20-23 Conrad DCF77 receiver module + level converter (Kit) 8.24-27 TimeBrick (limited availability ask time@informatik.uni-erlangen.de) 8.28-31 Meinberg GPS166 8.32-35 Trimble SV6 GPS receiver 127.127.9.x MX4200 GPS receiver 127.127.10.x Austron 2201A GPS Timing Receiver 127.127.11.x Kinemetrics Truetime OM-DC OMEGA Receiver 127.127.12.x KSI/Odetecs TPRO-S IRIG-B / TPRO-SAT GPS 127.127.13.x Leitch: CSD 5300 Master Clock System Driver 127.127.14.x MSFEES 127/127.15.x TrueTime GPS/TM-TMD 127.127.16.x Bancomm GPS/IRIG Ticktock 127.127.17.x Datum Programmable Time System