Motorola V186 User Manual - Page 146

System Time Control Actions, NTP Clock Synchronization

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Clock Functions and Synchronization system table, it also changes the RTU time and date. For more information on the Time & Date database system table, see Appendix C: Database Tables and Data Types in the ACE3600 STS User Guide. The user can update the same Time & Date database system table (HH:MM:SS) using the Application Programmer database monitor function. In this case, synchronization is direct (no time zone aspect.) For information on monitoring a database table, see the Application Programmer chapter of the ACE3600 STS User Guide. System Time Control Actions • GPS Connection - An RTU which is connected to a GPS receiver continuously polls the GPS time and synchronizes itself. Because the clock source is reliable, this RTU can be used to synchronize the rest of the system. See the Global Positioning System (GPS) section below. • NTP Connection - An RTU which is connected to an NTP server continuously polls the NTP server(s). Because the clock source is reliable, this RTU can be used to synchronize the rest of the system. The accuracy of NTP time depends on the link to the NTP server. It can be 1 millisecond in a LAN where the NTP server resides on the same network, and up to 100 milliseconds if using wireless media such as GPRS or TETRA. See the NTP Clock Synchronization section below. If the synchronizing RTU is in a different time zone than the RTU being synchronized, the system will adjust the time accordingly; the receiving RTU will add the time zone of the sender to the global time (GMT) and use this. If only one of the two RTUs involved is configured for time zone support, the synchronization will proceed as if both sites are in the same time zone. Note: A legacy MOSCAD RTUs is treated as an RTU which is not configured for time zone support. Note: In systems with I/O expansion, clock synchronization of the expansion modules is controlled by the main CPU. In addition, a sequencing mechanism ensures that time tags and timer events are sequenced properly in chronological order. NTP Clock Synchronization The Network Time Protocol (NTP) can be used as an external clock source to synchronize the ACE3600 RTU over IP with one or more NTP servers. In the MOSCAD system, the NTP works in client/server mode, in which a client RTU polls another server and gets a reply. The server can be another RTU operating NTP, or a host (PC, Unix, Linux). NTP poll the server RTU every 2 seconds, every 4 seconds, 8 and so on, up to a poll every 17 minutes. NTP provides client accuracies typically within a millisecond on LANs and up to 100 milliseconds on WANs (Internet, GPRS). Any 142

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Clock Functions and Synchronization
system table, it also changes the RTU time and date. For more information on the
Time & Date database system table, see Appendix C: Database Tables and Data
Types in the ACE3600 STS User Guide.
The user can update the same Time & Date database system table (HH:MM:SS)
using the Application Programmer database monitor function. In this case,
synchronization is direct (no time zone aspect.) For information on monitoring a
database table, see the Application Programmer chapter of the ACE3600 STS
User Guide.
System Time Control Actions
•
GPS Connection – An RTU which is connected to a GPS receiver continuously
polls the GPS time and synchronizes itself. Because the clock source is reliable,
this RTU can be used to synchronize the rest of the system. See the Global
Positioning System (GPS) section below.
•
NTP Connection – An RTU which is connected to an NTP server continuously
polls the NTP server(s). Because the clock source is reliable, this RTU can be
used to synchronize the rest of the system. The accuracy of NTP time depends on
the link to the NTP server. It can be 1 millisecond in a LAN where the NTP server
resides on the same network, and up to 100 milliseconds if using wireless media
such as GPRS or TETRA. See the NTP Clock Synchronization section below.
If the synchronizing RTU is in a different time zone than the RTU being synchronized,
the system will adjust the time accordingly; the receiving RTU will add the time zone of
the sender to the global time (GMT) and use this. If only one of the two RTUs involved is
configured for time zone support, the synchronization will proceed as if both sites are in
the same time zone.
Note: A legacy MOSCAD RTUs is treated as an RTU which is not configured for time
zone support.
Note: In systems with I/O expansion, clock synchronization of the expansion modules is
controlled by the main CPU.
In addition, a sequencing mechanism ensures that time tags
and timer events are sequenced properly in chronological order.
NTP Clock Synchronization
The Network Time Protocol (NTP) can be used as an external clock source to
synchronize the ACE3600 RTU over IP with one or more NTP servers.
In the MOSCAD system, the NTP works in client/server mode, in which a client RTU
polls another server and gets a reply.
The server can be another RTU operating NTP, or a
host (PC, Unix, Linux). NTP poll the server RTU every 2 seconds, every 4 seconds, 8
and so on, up to a poll every 17 minutes. NTP provides client accuracies typically within
a millisecond on LANs and up to 100 milliseconds on WANs (Internet, GPRS). Any
142