Nortel Networks Circuit Card - Manual (Page 729)

NTAK10 2.0 Mb DTI card Page 729 of 906
Circuit Card Description and Installation
converted from digital to AMI and sent to the carrier. A transformer provides
isolation and impedance matching (75 ohms or 120 ohms).
Rx Direction
The AMI data of the carrier is converted to digital and fed to the input selector
as well as the output selector for far end loopback. Clock recovery circuitry
within the receiving device extracts the 2.0 MHz clock. This clock generates
the frame and multiframe count and sends them to the clock controller as a
reference.
Clock controller interface
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, in conjunction with software, enables or disables 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 can be activated. All other DTI/PRI clock controllers must be
switched off.
Note: Clocking slips can occur between MG 1000S systems that are
clocked from different Central Offices (COs), if the COs are not
synchronized. The slips can degrade voice quality.
Clocking modes
The clock controller can operate in one of two modes: tracking or
non-tracking (also known as free-run).
IMPORTANT!
Each MG 1000S that has a digital trunk must have a clock controller
clocked to an external reference clock.