Model 5601MSC
Model 5601MSC Master SPG/Master Clock System
Page - 50 Revision 2.2 OPERATION
2.4. NETWORK TIME PROTOCOL (NTP)
If the 5601MSC is equipped with the T option, it will have an available Network Time Protocol (NTP)
server. The NTP server runs on both the CONTROL and the TIME Ethernet ports using the IP address
assigned each port. The NTP features are configured in the NTP Rules menu located in the GENERAL
root menu (see section 0).
The 5601MSC implements version 3 of the NTP protocol as defined in RFC 1305. The NTP server uses
the system clock as its source of time. This requires the system clock to be set to UTC in order to
generate a valid NTP timestamp. The NTP server also sends out unsolicited broadcast time packets
every 30 seconds on the CONTROL Ethernet port only. This is done to reduce traffic on the TIME
network. The contents of the packets are largely determined by the chosen time reference and the lock
status.
If the 5601MSC is not locked to the selected time reference, the LI_Alarm flag in all outgoing NTP
packets will be set. This informs clients that the NTP reference clock in the 5601MSC is not locked to a
reference. This flag is also set when the time reference is set to None. When this flag is set, most
clients will reject the time packet provided by the 5601MSC. This flag can be deactivated by enabling
NTP spoofing (see section 4.5.13.1). NTP spoofing should only be used for testing and troubleshooting
purposes as it technically breaks compliance with the NTP standard.
When an incoming client request for NTP time is received by the 5601MSC, the source IP address is
checked against a list of NTP restrictions (see section 4.5.13.2). There are a total of eight restrictions
and they are checked sequentially. If the incoming request passes all eight restrictions, the NTP server
will respond.
It is possible to perform a quick validation of NTP operation using a Windows XP or Windows 2000 PC
that is connected to the same network as the 5601MSC. For Windows XP Home edition, right-click on
the time display of the taskbar and select Adjust Date/Time. This will open up the Date and Time control
panel. There should be three tabs at the top: “Date & Time”, “Time Zone” and “Internet Time”. If the
“Internet Time” tab does not exist, use the command-line method below. Enter the IP address of the
5601MSC into the Server text box and click on the “Update Now” button. If the PC communicates with
the 5601MSC NTP server, the time should update successfully.
Another method is to use the “w32tm” utility from the command prompt. It may be necessary to install
the Windows Time Service before this command will be available. Open a command prompt window by
going to START->Programs->Accessories or by going to START->Run and typing in “
cmd”. Enter the
command “
w32tm /monitor /computers:172.21.1.56”. In this case 172.21.1.56 is the IP address of
the 5601MSC.
Figure 2-22: Testing the NTP Server
In the example above, the NTP server in the 5601MSC at 172.21.1.56 was successfully contacted. The
PC clock is 35 seconds advanced from the time provided by the 5601MSC. The RefID indicates that the
5601MSC is locked to GPS time.
C:\WINDOWS>w32tm /monitor /computers:172.21.1.56
172.21.1.56 [172.21.1.56]:
ICMP: 0ms delay.
NTP: +35.0868750s offset from local clock
RefID: 'GPS [71.80.83.0]
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