User guide

August 2001 89
Troubleshooting
For other loopback modes, disable both local and remote
loopbacks in CONFIG_CARRIER.
Test the cabling between the CSU and either the board or
the CO using a CSU loopback. In this mode, the CSU
immediately transmits all data it receives back to the CO
or board, depending on which end transmitted the data. To
do a CSU loopback, follow instructions from your CSU
manufacturer. Figure 15 shows two CSU loopbacks: one
looping data back to the CO and the other looping data
back to the board.
Figure 15. CSU Loopback
Test individual regions of the cabling using a cable to
connect transmit and receive leads at points along a trunk.
This mode loops data back to either the board or CO
depending on which end transmits the data and how you
set up the crossover cable.
For example, if you have identified that there is a problem
with the cabling between the CSU and the board, loop data
back at some point along the damaged cable. If the board
receives the same data it transmits, the cabling is good
between the loopback and the board. The problem lies
between the cable and the CSU. Continue testing until you
isolate the problem. Figure 16 shows a loopback using a
cable to physically connect the transmit and receive leads
along trunk A.
Figure 16. A Cabling Loopback in T1
Board CSU
Data stream to trunk A
Data stream from trunk A
CO
Board CSU
Data stream to trunk A
Data stream from trunk A
CO