Chapter 1 Overview of the TimeProvider

NTP Operation

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.

26 TimeProvider User’s Guide

097-58001-02 Revision G – April 2008

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Symmetricom 1100, 1000 manual NTP Operation, Ffoff Calculations