6
Issue 5, February 2011
61213075L2-5E
4. OPERATION
During normal operation the NIU3 PM is transparent to
the network. In the event of circuit trouble, test
equipment at the central office control terminal can
monitor the loop. When a loopback is initiated, the
transmit/receive paths can be tested to the customer
interface.
Monitoring
Front panel mid-size monitoring jacks provide nonin-
trusive monitoring access through a high-impedance
bridging circuit. The monitor level is nominally 21.5 dB
below the signal power. The signal to the network is
monitored via the
CUST TO NTWK MON
jack; the
signal to the customer is monitored via the
NTWK TO
CUST MON
jack.
Loss of Signal
In the event of a loss of signal, the NIU3 PM provides
both a “keep alive” signal and LED notification.
• If there is no signal from the network, the
NTWK
LOS/AIS
LED turns on red, and the NIU3 PM will
transmit an unframed all ones signal toward the
customer, while simultaneously transmitting RAI
towards the network.
• If there is no signal from the customer, the
CUST
LOS/AIS
LED turns on red, and the NIU3 PM will
transmit the signal selected by the
Customer LOS
option
on the
Provisioning
menu. The four selec-
tions that can be sent to the network upon customer
LOS are as follows:
– Framed Idle
– AIS
– No Signal
– AIS-CI
Loss of Framing
If either
NTWK
or
CUST C-BIT
and
M13
LEDs are both
off, the associated network or customer signal is
unframed.
If the NIU3 PM cannot detect framing in the signal from
the Network, then the NIU3 PM transparently passes
unframed data toward the Customer and RAI back
toward the Network.
If the NIU3 PM cannot detect framing in the signal from
the Customer, then the NIU3 PM transmits AIS-CI
toward the Network.
In the event that data transmitted through the circuit is
intended to be unframed, the AIS/RAI response to loss
of framing can be disabled via the Provisioning terminal
screen.
If the AIS/RAI response is disabled, then the NIU3 PM
will transparently pass unframed data from the Network
to the Customer and vice-versa.
provides a summary of the operation
of the NIU3 PM fault conditions.
