Dialogic Voice Cards - Triggering of clock fall back from primary to secondary clock

Introduction

Dialogic CG Series Media Boards may be configured with a primary and secondary clock source and auto fall back may be enabled. The secondary timing reference is used when the primary clock source fails. This article provides additional information about when fall back occurs and how clock sources are monitored.

Fall back triggering

A clock fall back occurs if the trunk that is providing the clock source goes into ALARM state.

The ALARM state is triggered when there is a Loss Of Signal (LOS) on the trunk. LOS detection is performed by monitoring logical zeros in a time interval of consecutive pulses; the boards are programmed so that if there are 176 consecutive 'zeros', LOS is flagged.  The LOS is recovered after 22 consecutive 'ones' are detected in a time interval. This implementation is in accordance with the ITU-T G.755 spec. 

Validation of clocks

On the trunk side, LOS is monitored constantly on all trunks so the clock manager can keep a track of which trunks have valid clocks. On the H.100 bus side, there is also watchdog running that monitors the clock constantly and reports to the clock manager, so the secondary clock is being checked all the time and not just when a fall back occurs. 

Product List

Dialogic CG Series Media Boards