Meinberg M900, Operating Instructions Manual, Page: 12 / 170

SHS Mode
GPS:SYN PZF:SYN
NTP:SYN SHS:0ms
Thu, 01.01.2008
UTC 12:00:00
Secure Hybrid System with Strongly Verificated Reference Time
Meinberg LANTIME devices are Stratum-1 time servers which provide a high-
accuracy reference time to TCP/IP networks via the Network Time Protocol (NTP).
The main difference between the LANTIME models is the primary time source from
which a device derives its reference time. Primary time source options include
external radio clocks, built-in DCF77, GPS, or IRIG receivers, and even a hybrid
combination of a DCF77 and a GPS receiver.
The M300/SHS (Secure Hybrid System) has a built-in hybrid radio clock which
derives its reference time from both the satellite based Global Positioning System
(GPS) and long wave receiver PZF5xx. During normal operation the hybrid radio
clock passes the highly accurate reference time on to the built-in NTP time server
which makes the reference time available to the network.
In order to prevent the NTP server from spreading a faulty reference time in the
network, the hybrid receiver includes two independent standard radio clocks. Both the
satellite receiver GPS170 and the long wave receiver PZF5xx have their own signals
and high quality crystal oscillators which let the radio clocks provide accurate time
even if their primary time transmitters cannot be received for a few days.
The two radio clocks derive their time telegrams and high accuracy pulse-per-second
(PPS) signals from two independent primary time sources. The time telegrams and the
PPS signals output by the clocks are compared against each other. If either the
difference between the time telegrams or the difference between the PPS signals
exceeds a configurable limit of some milliseconds the internal NTPD will be stopped.
If it is necessary to provide redundancy against hardware failure then it is also
possible to install several LANTIME NTP servers in the same network.
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