Chapter 24 – Configuring IRIGB And IEEE1588
NTP The PTP clock is a secondary reference standard reference clock. The router uses
this identifier when it has synchronized with remote NTP server.
DFLT After the router has power cycled but before any GPS or NTP locks have occurred.
PTP favors preferred masters over normal masters, GPS over NTP over DFLT, higher
clock stability over lower clock stability.
Synchron izing NTP f rom IEEE158 8
If GPS is unavailable and PTP becomes a slave the NTP server will view the received
IEEE1588 time as any other source of time. The quality (i.e. stratum) of IEEE1588
information is determined by the type of clock source at the master, the number of
Boundary Clock hops and the measured network jitter.
The number of Boundary Clock hops is the number of IEEE1588 devices the original
time source is relayed through (and not Ethernet hops) and is always 1 or higher.
The measured network jitter factor is 0 if jitter is higher than 1 microsecond and -1 if
less than 1 microsecond.
PTP Identifier Stratum reported to NTP
GPS 1 + Number of Hops ? 1 (if low jitter)
NTP user configurable value (default 2) + Number of Hops ? 1 (if low jitter)
DFLT user configurable value (default 10) + Number of Hops ? 1 (if low jitter)
The stratum number reported will be limited to a range of 1 to 16 to comply with
NTP.
As an example, a directly connected PTP clock having a GPS clock source and low
jitter would report a stratum of 1. With defaults a 2 hop away PTP clock having a
NTP clock source and high jitter would report a stratum of 4.
IRIGB Fu ndamentals
IRIGB outputs are provided by the Precision Time Protocol Card option.
The Inter-Range Instrumentation Group (IRIG) IRIG-B standard details the format of
an output signal containing information for the current day, hour, minute and second
in UTC format, broadcast at the start of each second. The RuggedRouter complies to
IRIG Standard 200-04 generating formats IRIGB002 and IRIGB003 (PWM) and
IRIGB122 and IRIGB123 (AM).
IRIGB O utput Forma ts
The router provides three ports by which the signal is distributed, namely:
•An Amp litude Modulat ed (AM) sinusoi dal out put por t (PTP1) ,
•Two TTL voltage level output ports (PTP2 and PTP3) which may be
configured as either pulse per second (PPS) or pulse width modulated (PWM).
The signal can be used to synchronize intelligent devices to a high quality time
source, called the reference clock. The router uses a global positioning satellite
(GPS) receiver, NTP or the router's local clock as the reference clock.
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