Nortel Networks 311 Free-run (non-tracking)

908 NTAK20Clock Controller daughterboard

If the incoming reference is unstable, the internal clock controller remains

continuously 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.

In tracking mode, one or more DTI/PRI cards supply a clock reference to the

NTAK20clock 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 deﬁnedin LD 73.

There are two stages to clock controller tracking:

•tracking a reference

•locking on to a reference

When tracking a reference,the clock controller uses an algorithm to match

its frequency to the frequency of the incoming clock. When the frequencies

are almost matched, the clock controller locks on to the reference. The

clock controller makes small adjustments to its own frequency until both the

incoming and system frequencies correspond.

If the incoming clock reference is stable, the internal clock controller

tracks it, locks on toit, and matches frequencies exactly. Occasionally,

environmental circumstances cause the external or internal clocks to vary.

When this happens, the internal clock controller brieﬂy enters the tracking

stage. The green LED ﬂashes until the clock controller is locked on to the

reference again.

If the incoming reference is unstable, the internal clock controller

continuously tracks,and the LED continuously ﬂashes green. This condition

does not present a problem. It shows that the clock controller is continually

attempting to lock onto the signal. If slips occur, 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 outside

source. Instead, it provides its own internal clock to the system. This mode

can be used when the system acts as a master clock source for other

systems in the network. Free-run mode is undesirable if the system is

intended to be a slave to an external network clock. Free-run mode can

occur when both the primary and secondary clock sources are lost due to

hardware faults or invokedusing software commands.

Nortel Communication Server 1000

Circuit Card Reference

NN43001-311 01.04 Standard

Release 5.0 23 May 2008