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4 Section 61212075L1-5, Issue 3 61212075L1-5C
If CPE, (e.g. DS3 multiplexer), is within 225 line feet
of the NIU3, enable LBO on SW2-2.
• SW2 Position 2 – ON, LBO toward customer
enabled
• SW2 Position 2 – OFF, LBO toward customer
disabled
LED Indication
Four LEDs on the NIU3 front panel show status
during normal, problem, and test operation. Table 1
describes LED indication.
Initiating Loopback with SW1
Front panel LBK SEL pushbutton (SW1) controls
loopback mode as described here:
• To initiate a loopback, depress SW1 for 5
seconds. During this time the LBK LED flashes
indicating the loopback is “arming.” After 5
seconds the loopback enables, the LED turns ON
solid, and SW1 can be released.
If SW1 is released before the arming period expires
the loopback does not initiate. This process decreases
the chance of an inadvertent loopback.
• If a loopback is in affect, depressing SW1 will
disable the loopback regardless of initiation
point.
Loopback priority is in response to the most recent
local or remote input. The LBK LED shows status.
3. TURNUP
When inserted into a host with power, the PWR LED
turns ON red while the NIU3 performs a self-test
during which the remaining LEDs go through an ON/
OFF sequence. If the self-test passes, the PWR LED
turns ON green indicating the NIU3 is online. If the
test fails, the LED remains red and the host bypass
relays will maintain data flow around the NIU3.
4. OPERATION
During normal operation the NIU3 is transparent to
the network. In the event of circuit trouble, test
equipment at the central office can monitor the loop.
When a loopback is initiated, the transmit/receive
paths can be tested to the customer interface. The
NIU3 troubleshooting tests are intrusive to data
transmission.
Monitoring
Front panel mid-size monitoring jacks provide
nonintrusive monitoring access through a
high-impedance bridging circuit. The monitor level is
nominally 21.5 dB below the signal power. The signal
from the network is monitored via the NTWK MON
jack; the signal from the customer is monitored via the
CUST MON jack.
Loss of Signal
In the event of a loss of signal, the NIU3 provides
both a “keep alive” signal and LED notification.
• If there is no signal present from the network, the
NTWK LED turns ON red and the NIU3 will
transmit an unframed all ones signal toward the
customer.
• If there is no signal present from the customer,
the CUST LED turns ON red and the NIU3 will
transmit a framed DS3 idle signal toward the
network.
Table 1. LED Indication
DELroloCsutatSnoitpircseD
RWP
neerG
deR
NO
NO
FFO
.noitarepolamroN
.noitcnuflaMdraC
.rewopoN
KWTN
deRNO
FFO
.ecafretnikrowtentalangis3SDoN
.ecafretnikrowtentatneserplangis3SD
TSUC
deRNO
FFO
.ecafretniremotsuctalangis3SDoN
.ecafretniremotsuctatneserplangis3SD
KBL
wolleYgnihsalF
NO
FFO
.gnimrakcabpooL
.delbanekrowtendrawotkcabpooL
.delbasidkrowtendrawotkcabpooL
.noitcnuflammetsysrehtoro,rewoponsetacidniFFOsDELllA:etoN