Clock Controller Interface - Nortel Enterprise 1000 Reference Manual

Page 152 of 236

Clock controller interface

553-3023-211 Standard 1.00 June 2001
NTAK10 2.0 Mb DTI card
Each Media Gateway that has a digital trunk must have a
clock controller clocked to an external reference clock.
Note: Clocking slips can occur between Media Gateways that are
clocked from different COs, if the COs are not synchronized. The slips
can cause degraded voice quality.
The recovered clock from the external digital facility is provided to the clock
controller through the backplane-to-clock controller interface. Depending
upon the state of the clock controller (switched on or off), the clock controller
interface will, in conjunction with software, enable or disable the appropriate
reference clock source.
The clock-controller circuitry on NTAK10 is identical to that of the
NTAK20. While several DTI/PRI packs can exist in one system, only one
clock controller may be activated. All other DTI/PRI clock controllers must
be switched off.
Clocking modes
The clock controller can operate in one of two modes: tracking or non-
tracking (also known as free-run). See "Clocking modes" on page 27.Clock
controller functions and features
The NTAK10 2MB DTI clock controller functions and features include:
• phase-locking to a reference, generating the 10.24 Mhz system clock,
and distributing it to the CPU through the backplane. Up to two
references at a time may be accepted.
• providing primary to secondary switchover and auto-recovery
• preventing chatter
• providing error burst detection and correction, holdover, and free
running capabilities
• complying with 2.0 Mb CCITT specifications.
IMPORTANT