9500 MXC User Manual
3DB 23063 ADAA - Rev 004 July 2007 Vol. IV-15-59
While PRBS Generation is ON:
• INU/INUe: The NCC Test LED flashes orange and the diagnostic icon is
displayed in the CT status bar.
• IDU: The IDU Status LED flashes orange and the diagnostic icon is displayed
in the CT status bar.
Auto Insertion of AIS or PRBS on Tribs
This topic covers auto insertion of AIS/PRBS on tribs when:
• A demodulator unlock occurs
• Loopbacks are set
Demodulator Unlock
When a RAC/radio demodulator-unlock occurs, it inserts an alarm signal (AIS or
PRBS15) on all traffic circuits towards the bus/customer. All cross-connected
circuits from this RAC/radio, which for a Node may be to DAC and/or other
RAC plug-ins, will carry this AIS/PRBS. At a DAC/trib, the affected tributaries
will carry AIS/PRBS on the outgoing customer connection. Demodulator unlock
may occur under severe fading or an equipment fault.
• For all E1, DS1, E3, DS3 DACs/IDUs, AIS is inserted on the affected data-out
tributaries (towards the customer).
• For all STM1/OC3 DACs/IDUs, a PRBS15 pattern (15 bit pseudo-random bit
sequence) is inserted on the affected data-out tributaries (towards the
customer).
An on-board master clock within DACs/IDUs maintains customer-facing
clocking references when the expected signal input and associated clocking
reference from its RAC/radio is missing, or below the minimum level required.
Loopbacks
When loopbacks are applied:
•For a PDH radio-facing tributary loopback, AIS is transmitted on the affected
tributary towards the customer.
• For an SDH radio-facing tributary loopback, PRBS is not transmitted on the
affected tributary towards the customer (an external BERT will indicate a loss
of frame alarm).
•For a line-facing tributary loopback, and for a digital loopback, AIS/PRBS is
not transmitted. Instead, as well as traffic from the customer being looped back
towards the customer, it is also transmitted in the radio facing direction of the
affected circuit(s).
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