Verilink QUAD T1 (880-503345-001) Product Manual User Manual
Page 48
Diagnostics and Alarms
5-6
Verilink QUAD T1 User Manual
Loopback Plug
For a completely reliable test of a QUAD T1 module, make a T1
loopback plug and plug it in to a network port. The module will
now receive the signals it is sending on that port.
If the port is sending a defective signal, it will receive a defective
signal and declare an alarm. If the receive circuitry is defective,
such that it cannot decode a good signal, it will be unable to decode
the signal it is transmitting and will declare an alarm. Thus, if a T1
port does not declare any alarms with a loopback plug in lieu of the
T1 circuit, that port is not defective. This does not rely on any tests
built in to the product, thereby producing a higher confidence level
in the results of the test.
With a loopback plug in a QUAD T1 module port, any circuit built to
the port should see a loopback condition. If the customer
equipment can report errors, it should indicate that no errors are
being received.
A T1 loopback plug can be made by placing two short jumper wires
on a male RJ-45 connector where a cable would normally go. One
jumper is placed from pin 1 to pin 5, the other jumper connects pin
2 to pin 4. See
for
a drawing of an RJ-45 connector
showing pin positions and wiring of a T1 loopback plug.
NOTE: When using a T1 loopback plug, it may be necessary to
temporarily change the timing selection in the QUAD T1
module. If the shelf is set to recover network clock from the
port being tested, it will be trying to recover a clock it is
trying to recover. The clock frequency will drift. For this test,
the shelf should not be timed by the port being tested.
CRC errors
ESF T1 circuits offer CRC-6 error checking as a means of detecting changes
in data that occur on the T1 circuit.
If CRC errors are reported, the errors are occurring at some point between
the two CSUs. Verify in-house wiring as indicated above.
Contact the carrier and request they monitor the circuit. Carriers can
monitor a T1 circuit for CRC errors without disrupting user data.
BPV
A bipolar violation is a sequence of two or more consecutive pulses of the
same polarity.
If a T1 is designed to support B8ZS, but some portion of the facility is
configured for AMI in error, the AMI portion of the T1 may attempt to “fix”
the intentional bipolar violations used to represent 8 or more zeros on a
B8ZS T1.
This may manifest as BPVs or BPVs with CRC-6 errors.
To verify that a T1 which is intended to be B8ZS is actually configured
properly, test the facility with a pattern of all zeros.
Trouble
Suggestion