Verilink QUAD T1 (880-503345-001) Product Manual - Manual (Page 47)

Diagnostics and Alarms
Verilink QUAD T1 User Manual 5-5
Table 5-2 Troubleshooting Tips
Trouble Suggestion
CRC errors and BPVs
reported on a new
installation
When a T1 presents symptoms of CRC errors and BPVs, with no other
alarms, it often is traced to problems with wiring inside the customer
premise.
When the smart jack is a considerable distance from the QUAD T1 module
(over 50 feet), there is the risk that the high level (hot) signals in the
transmit pair will induce echo into the lower level (long) signals in the
receive pair. This condition is called crosstalk and is a leading cause of T1
problems.
As telephone carriers move toward a policy of housing all smart jacks in one
location within commercial buildings, crosstalk related complaints are
becoming more common.
To prevent crosstalk related issues, the transmit pair and the receive pair
must be isolated from each other.
The recommended cable for T1 uses individually shielded, twisted pairs;
each pair has shielding around it—the cable therefore has two shields inside
it, one for each pair.
If shielded twisted pair cable is not available, try to route the transmit pair
and the receive pair in different cables as they traverse the building.
If the transmit and receive pairs must be routed through a multi-pair cable,
such as the 25-pair or 50-pair cables found in large office buildings, select
pairs that are not near each other in the cable.
Many smart jacks offer an option “regeneration”. This causes the smart jack
to increase the amplitude of the signal received from the network before
handing it off to the CSU. This causes the signal on the receive pair to have a
higher amplitude, closer to the signal level in the transmit pair—thus
reducing the tendency to crosstalk. Try to get the carrier to turn on this
option.
Loss Of Signal Verify that a T1 circuit or device is connected to the port indicating LOS.
Verify that a proper cable is used. T1 circuits use pins 1,2,4 and 5 when
presented in an RJ-45 connector. Use a straight through cable (1 to 1, 2 to 2,
etc.).
For a port facing a T1 circuit, the smart jack (network termination device)
may be in a loopback. Examine the smart jack. If it has an LED labelled Loop,
LP, or LB and that LED is lit—the smart jack is in a loopback. Contact the
network service provider.
For a port facing local DSX-1 equipment, the equipment (PBX, channel bank,
etc.) may have stopped using the facility, check status menus on that device.
Loss Of Frame In a new installation, T1 circuits are often patched out at a carrier’s DACS or
switch until completely turned up. In this case a pattern of unframed all
ones (AIS) is kept on the T1 as a keep-alive signal. Contact the carrier and
request that they “normal up” the circuit.
The QUAD T1 module must be optioned for the same type of framing as the
T1 carrier is providing. Framing can not be changed arbitrarily by the user.
Contact the carrier and verify the type of framing used on the T1.