XLi Time & Frequency System 283
XLi-man, Issue 8, 6/17/2008, Rev. H
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SSSSSSSSSSSS SSSSSSSSSS SSSSSSS S SSS S SSSSS S
D: Network Time Protocol (NTP)
As an option, Symmetricom can factory configure the XLi to function as a Stratum 1 network time server.
Network time servers use Network Time Protocol (NTP) to synchronize computer clocks across a
network.
Support for version 4.0 of the NTP, RFC 1305 as well as the Simple Network Time Protocol (SNTP),
RFC2030 is available. In addition, the XLi responds to TIME protocol requests, RFC868.
The Network Time Server responds to time synchronization requests from hosts using these User
Datagram Protocol/Internet Protocols (UDP/IP):
NTP Packet Transmitted Timestamp Accuracy ±10 milliseconds
Leap Indicator
After the XLi has entered a holdover state (“flywheeling” on its internal oscillator or Aux Ref while a time
reference is absent) for "n" hours, the Leap Indicator transitions to "11" and the Stratum Level stays at
"1". "n" is dependent upon the XLi reference oscillator. When an internal phase error within the NTP
server is greater than 1 millisecond the Leap Indicator will transition to unsynchronized ("11"). This can
take a very long time when an OCXO or Rb is installed in the XLi.
* n is dependent upon the XLi reference oscillator
Editing ntp.conf
Note: The XLi is a Stratum 1 NTP server. Therefore, it does not support NTP peering, in which a time
server gets time information by sending an NTP query to another time server. Entering valid IP
addresses for the ‘server’ parameters (e.g., “
server 216.210.169.40”) in ntp.conf does not
enable peering in the XLi.
The current text of “ntp.conf” is as follows:
Type/Protocol Port Number RFC
NTP ver. 4.0: UDP Port 123 RFC1305
SNTP: UDP Port 123 RFC2030
TIME: UDP Port 37 RFC868
XLi Operational State
Stratum LI
Power ON 1 11
GPS Locked 1 00
GPS Unlocked 1 00
GPS Unlocked (after n
hours)*
111
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