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S100 User Guide – Rev. D – June 2005 9
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Time Distribution ModelNetwork time distribution systems use a hierarchical time distribution model, as shown in this
figure:
In hierarchical systems, primary time source clocks are Stratum 0 (zero), including GPS
satellites, National Institute of Standards and Technology (NIST) ACTS dial-up service, or
similar national time standards organizations.
The S100 acts as a Stratum 1 time server that derives its time from GPS and distributes this
time over a TCP/IP network using NTP. Stratum 2 NTP client s can distribute time to S tr atum 3
computers.
How the S100 WorksThe following describes how the S100 acquires and secures time.
Computer
Systems
(NTP
Clients)
SyncServers
or Computer
Systems
(NTP Clients)
Symmetricom
SyncServer
GPS
Satellites or
NMI Dial-Up
Service
Stratum 3 Stratum 2 Stratum 1 Stratum 0
Figure 2-1: The S100 in the Time Distribution Hierarchy