Symmetricom EDGE CLOCK 1000 - Manual (Page 26)

Chapter 1 Overview of the TimeProvider
NTP Operation
26 TimeProvider User’s Guide 097-58001-02 Revision G – April 2008
FFOFF Calculations
FFOFF is a measure of the frequency deviation of the input signal against the
system reference, expressed as a ratio. The TimeProvider automatically calculates
FFOFF for each enabled input from the 600 most recent 1-second phase updates.
You can use the automatic FFOFF calculations to qualify each input with
user-defined qualification thresholds. If an input exceeds the threshold and the
alarm level is set to Minor or higher, then the input reference automatically switches
to the next-best input.
The TimeProvider stores historical FFOFF measurements for each enabled input
every 60 seconds. You can retrieve FFOFF data for the prior 24 hours, depending
on the number of faults that have occurred.
NTP Operation
The Network Timing Protocol (NTP) function is implemented in the IMC card or
IMC/TPIU card. You can activate the NTP feature by issuing a unique key
generated by Symmetricom, based on the serial number of the IMC card or the
IMC/TPIU card, or you can order the TimeProvider with the NTP option factory-
installed and activated. Once activated, the NTP function cannot be deactivated.
NTP operates in all three operating modes of the TimeProvider. In the Subtending
mode, the NTP server is supported when the system reference is a signal other
than GPS. The NTP data is transmitted by the Ethernet port on the shelf, and meets
the following standards and specifications:
NTP V3
MD5 Authentication (RFC 1321)
NTP Leap Second correction based on GPS
NTP supports a 10baseT connection under a 40% loading condition, and can
handle up to 100 requests per second (RPS) on average
Typical unencrypted response time from the TimeProvider on an unloaded
network is < 10 ms
Typical encrypted (MD5) response time from the TimeProvider on an unloaded
network is < 50 ms
The client time accuracy is typically 2 ms between the internal NTP clocks of two
machines on the same 10 Mb/s Ethernet LAN with a 40% loading condition
Note: NTP over a LAN topology depends on network congestion, and
can be up to 50 ms accuracy.