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S100 User Guide – Rev. D – June 2005 9
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Time Distribution Model
Network 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 clients can distribute time to Stratum 3
computers.
How the S100 Works
The 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