Ntp Reference Configuration - Spectracom VersaSync User Manual

2.7 Configuring Network Settings
2.7.8.7

NTP Reference Configuration

VersaSync'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 VersaSync'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 VersaSync will be the Stratum 1 (or primary) server. This is
the most common configuration.
b.
It is, however, also possible for NTP to utilize the time provided by
as a reference. In this case the other server would be Stratum 1, and VersaSync would
be Stratum 2 (or higher). This operating mode can be referred to as Stratum 2 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
page 131.
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.
Stratum 0 means a device is directly connected to e.g., a GPS antenna. Stratum 0 devices can-
not distribute time over a network directly, though, hence they must be linked to a Stratum 1 time
server that will distribute time to Stratum 2 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
Peers to each other. NTP Servers at a
as NTP Servers
If VersaSync 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 VersaSync unit as a time reference.
Configuring "NTP Stratum 1" Operation
When the Timing System references of your VersaSync are normally available (rather than
being unavailable most of the time e.g., in areas with poor GNSS reception), it is advisable to
use the System Time as a reference to NTP, since this provides NTP with the most accurate ref-
erences. This mode is called Stratum 1 operation, since VersaSync operates as a Stratum 1 NTP
server.
84
.
Note: Internet Time Servers should be configured as NTP Servers and not as NTP
Peers.
higher
Stratum level, on the other hand, are referred to
CHAPTER
2
another
NTP Server
NTP
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VersaSync User Manual Rev. 6.0