Nortel Networks 553-3001-211 manual NTAK79 2.0 Mb PRI card Page 747

NTAK79 2.0 Mb PRI card Page 747 of 894

If the incoming clock reference is stable, the internal clock controller will track it, lock onto it, and match frequencies exactly. Occasionally, however, environmental circumstances will cause the external or internal clocks to drift. When this happens, the internal clock controller will briefly enter the tracking stage. The green LED will flash momentarily until the clock controller is locked onto the reference once again.

If the incoming reference is unstable, the internal clock controller will continuously be in the tracking stage, with the LED flashing green all the time. This condition does not present a problem, rather, it shows that the clock controller is continually attempting to lock onto the signal. If slips are occurring, however, it means that there is a problem with the clock controller or the incoming line.

Free-run (non-tracking)

In free-run mode, the clock controller does not synchronize on any source, it provides its own internal clock to the system. This mode can be used when the CS 1000S, CS 1000M Cabinet, and Meridian 1 PBX 11C Cabinet are used as a master clock source for other systems in the network. Free-run mode is undesirable if the CS 1000S, CS 1000M Cabinet, and Meridian 1 PBX 11C Cabinet are intended to be a slave. It can occur, however, when both the primary and secondary clock sources are lost due to hardware faults or when invoked by using software commands.

Clock controller functions and features

The NTAK79 clock controller functions and features include:

•phase lock to a reference, generate the 10.24 MHz system clock, and distribute it to the CPU through the backplane. Up to two references at a time are accepted

•primary to secondary switchover (auto-recovery is provided)

•prevent chatter

•error burst detection and correction, holdover, and free running capabilities

•compliance with 2.0Mb CCITT specifications

•software communication

Circuit Card Description and Installation