2.14.7 NTP Reference Configuration
SecureSync's NTP Service needs to be setup such that it utilizes the time source ("input ref-
erence") you want it to use. There are two options for an NTP Server to derive its time from:
a.
The NTP Service uses SecureSync's System Time, i.e. typically the GNSS reference (or
IRIG, ASCII data input, etc.), and distributes that time over the NTP network. This is called
Stratum 1 Operation, because SecureSync will be the Stratum1 (or primary) server. This
is the most common configuration.
b. It is, however, also possible for NTP to utilize the time provided by
another
NTP Server
as a reference. In this case the other server would be Stratum 1, and SecureSync would
be Stratum 2 (or higher). This operating mode can be referred to as Stratum2 operation,
secondary server operation, or NTP Stratum Synchronization.
With a GNSS-capable time server it is possible to combine these two configurations e.g., by
assigning a higher reference priority to (a.), and a lower "fallback" priority to (b.). For more
information on reference priority configuration, see "Configuring Input Reference Priorities" on
page163.
2.14.7.1 The NTP Stratum Model
The NTP Stratum model is a representation of the hierarchy of time servers in an NTP network,
where the Stratum level (0-15) indicates the device's distance to the reference clock.
Stratum0 means a device is directly connected to e.g., a GPS antenna. Stratum0 devices can-
not distribute time over a network directly, though, hence they must be linked to a Stratum1 time
server that will distribute time to Stratum2 servers or clients, and so on. The higher the Stratum
number, the more the timing accuracy and stability degrades.
The NTP protocol does not allow clients to accept time from a Stratum 15 device, hence Stratum
15 is the lowest NTP Stratum.
A group of NTP servers at the same Stratum level (Stratum 2, for example) are considered NTP
Peers to each other. NTP Servers at a
higher
Stratum level, on the other hand, are referred to
as NTP Servers.
Note: Internet Time Servers should be configured as NTP Servers and not as NTP
Peers.
If SecureSync has no valid Timing System Reference, NTP Server or NTP Peers, the NTP Stratum
value is automatically downgraded to Stratum 15. This ensures that its NTP clients will no longer
use this SecureSync unit as a time reference.
2.14.7.2 Configuring "NTP Stratum 1" Operation
When the Timing System references of your SecureSync are normally available (rather than
being unavailable most of the time e.g., in areas with poor GNSS reception), it is advisable to
102
CHAPTER 2 • SecureSync User Reference Guide Rev. 26
2.14 Configuring NTP
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