Clocking Modes - Avaya Nortel Communication Server 1000 Reference

NTAK20 Clock Controller daughterboard
Important:
Each Media Gateway that has a digital trunk must have a clock controller clocked to an
external reference clock.
If an IP Expansion multi-cabinet system is equipped with digital trunk cards, it is mandatory
that at least one trunk card is placed in the Main cabinet.
Note:
Clocking slips can occur between systems that are clocked from different COs, if the COs
are not synchronized. The slips can degrade voice quality.
The clock controller circuitry synchronizes the system to an external reference clock and
generates and distributes the clock to the system. The system can function either as a slave
to an external clock or as a clocking master. The NTAK20AD version of the clock controller
meets the AT&T Stratum 3 and Bell Canada Node Category D specifications. The NTAK20BD
version meets CCITT Stratum 4 specifications.
The NTAK20 card performs the following functions:
• phase lock to a reference, generation of the 10.24 Mhz system clock, and distribution of
the clock to the CPU through the backplane
• accept one primary and one secondary reference
• primary-to-secondary switchover and auto-recovery
• chatter prevention due to repeated switching
• error-burst detection and correction, holdover, and free running capabilities
• communication with software
• jitter filtering
• use of an algorithm to detect crystal aging and qualify clocking information

Clocking modes

The clock controller can operate in one of two modes: tracking or non-tracking (also known as
free-run).
Tracking mode
In tracking mode, one or more DTI/PRI cards supply a clock reference to the NTAK20 clock
controller daughterboard. When operating in tracking mode, one DTI/PRI card is defined as
the Primary Reference Source (PREF) for clock synchronization. The other DTI/PRI card is
defined as the Secondary Reference Source (SREF). PREF and SREF are defined in LD
73.
514 Circuit Card Reference
Comments? infodev@avaya.com
July 2011