Symmetricom 1100, 1000 manual SSMs and Quality Level, SSU Mode

Chapter 1 Overview of the TimeProvider

Reference Input Signals

provision the REFMODE parameter to FORCED to select an input as the system reference regardless of the priority levels of other outputs. If this input is lost or is disqualified, then the REFMODE automatically changes to AUTO and the next available reference based on priority and QLEVEL becomes the system reference. If no other input references are available, the TimeProvider enter the Holdover mode.

The QLEVEL (Setting the Input Quality Level, on page 112) and the PRIORITY

(Setting the Input Priority Level, on page 113) parameters work together with SSMs to determine the switching strategy for the inputs when the unit is in the SSU mode. If the active/primary input becomes unavailable, the switching strategy determines which input to use: the TimeProvider uses the input with the next highest QLEVEL. If all inputs have the same QLEVEL, then the TimeProvider uses the input with the highest PRIORITY.

To provision the TimeProvider as non-revertive, you must provision the user-assigned Priority Level on all inputs to the same value. To provision the TimeProvider as revertive, you provision any one of the inputs to a different Priority Level.

If the original primary input becomes available again, the REFMODE, QLEVEL and PRIORITY parameters determine whether the TimeProvider switches back to that input. If REFMODE is set to AUTO, then the reference switches according to the QLEVEL and PRIORITY settings. If the QLEVEL and/or PRIORITY parameter of the original input is higher than the current input, the TimeProvider reverts back to the original input. If the QLEVEL parameter is the same for all inputs, then the TimeProvider does not revert back to the original input.

SSMs and Quality Level

Synchronization Status Messages (SSMs) can be included in the bit stream of the incoming signal to indicate its quality level. You must provision the input to read the SSM, and you must provision the bit position of the incoming SSM.

If the incoming signal does not include SSMs, or if you disable them, then you can provision the Quality Level to an appropriate value. The QLEVEL value is used in the same manner as the incoming SSM to determine which input is used when the active input is disqualified. SSMs are described in more detail in Synchronization Status Messages (SSMs), on page 41.

SSU Mode

Table 1-2illustrates which input is the active system reference under several different input conditions when the TimeProvider is in the SSU mode.

36 TimeProvider User’s Guide 097-58001-02 Revision G – April 2008