NTP REFID Specification

The NTP REFID specifies a string of 4 ASCII characters that defines the reference identifier used by the driver.
The REFID string overrides the default identifier ordinarily assigned by the driver itself.

The following is an excerpt of the NTPv4 RFC:

NTPv4 Specification                                       June 2010


Root Delay (rootdelay): Total round-trip delay to the reference
clock, in NTP short format.


Root Dispersion (rootdisp): Total dispersion to the reference clock,
in NTP short format.


Reference ID (refid): 32-bit code identifying the particular server
or reference clock.  The interpretation depends on the value in the
stratum field.  For packet stratum 0 (unspecified or invalid), this
is a four-character ASCII [RFC1345] string, called the "kiss code",
used for debugging and monitoring purposes.  For stratum 1 (reference
clock), this is a four-octet, left-justified, zero-padded ASCII
string assigned to the reference clock.  The authoritative list of
Reference Identifiers is maintained by IANA; however, any string
beginning with the ASCII character "X" is reserved for unregistered
experimentation and development.  The identifiers in Figure 12 have
been used as ASCII identifiers:


+------+----------------------------------------------------------+
| ID   | Clock Source                                             |
+------+----------------------------------------------------------+
| GOES | Geosynchronous Orbit Environment Satellite               |
| GPS  | Global Position System                                   |
| GAL  | Galileo Positioning System                               |
| PPS  | Generic pulse-per-second                                 |
| IRIG | Inter-Range Instrumentation Group                        |
| WWVB | LF Radio WWVB Ft. Collins, CO 60 kHz                     |
| DCF  | LF Radio DCF77 Mainflingen, DE 77.5 kHz                  |
| HBG  | LF Radio HBG Prangins, HB 75 kHz                         |
| MSF  | LF Radio MSF Anthorn, UK 60 kHz                          |
| JJY  | LF Radio JJY Fukushima, JP 40 kHz, Saga, JP 60 kHz       |
| LORC | MF Radio LORAN C station, 100 kHz                        |
| TDF  | MF Radio Allouis, FR 162 kHz                             |
| CHU  | HF Radio CHU Ottawa, Ontario                             |
| WWV  | HF Radio WWV Ft. Collins, CO                             |
| WWVH | HF Radio WWVH Kauai, HI                                  |
| NIST | NIST telephone modem                                     |
| ACTS | NIST telephone modem                                     |
| USNO | USNO telephone modem                                     |
| PTB  | European telephone modem                                 |
+------+----------------------------------------------------------+

NTP Reference IDs (REFID) used by Meinberg Products

Meinberg products like the LANTIME family of NTP time server appliances or the PCI/PCIe slotcards and USB reference clocks extend the above listed reference ID strings in order to distinguish sub types. For example: the two REFID strings "DCFa" and "DCFp" both indictate that DCF77 is the reference time signal. The "a" is appended for Meinberg clocks that use the standard amplitude modulated signal, whereas the "p" indicates that the Meinberg receiver is using the phase modulated pseudo-random noise receiver technology that is more accurate than the AM reception approach.

The appended subtypes "i" and "s" are recommended REFID strings for Meinberg reference clocks handled by the Meinberg bus-level product drivers. The "i" indicates that the driver is running in "interrupt" mode, basically emulating a serial time string that is used by the NTP parse refclock driver (type 8). The "s" is used in our driver documentation as a recommendation to indicate that the clock is using the shared memory refclock driver of NTP (SHM, type 28).

For example, a Meinberg GPS180PEX PCIe card using the latest driver software is using the SHM refclock driver of NTP, therefore we recommend to use the "refid" configuration directive of NTP to change the refid of this stratum 0 clock to "GPSs", for a TCR170PCI card using the interrupt driven approach we recommend configuring the refid to "TCRi".

The Meinberg LANTIME NTP appliances are using the parse driver approach for all the internal refclocks that are connected via a serial connection to the LANTIME NTP CPU. The SyncFire 1000 appliance comes with one or two PCIe reference clocks, either a GPS180PEX or a GLN180PEX. Both are utilized as reference clocks for NTP with the shared memory driver (SHM). Therefore the refid used in these high performance NTP servers is either "GPSs" or "GLNs"