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Chapter 5
Troubleshooting
Table 5-5
Line Card Problems (continued)
Symptom
Port fails to come up (modems
do not train), or port LED
flashes continuously.
You suspect a problem with the
CPE or the subscriber loop.
OL-2365-01
Steps to Take
Enter the command show dsl int atm slot#/port# to display the port configuration.
1.
Check the display to ensure that the port is properly provisioned. Make sure the port
is configured to be running ("no shutdown" or IOS admin state = up). Also check the
line status; if this reads "No CPE detected," troubleshoot the CPE device and the loop
as described below under the symptom
subscriber loop." section on page
In interface configuration mode, reset the port by executing the shutdown command
2.
followed by the no shutdown command.
Connect the subscriber to another port on the Cisco 6260. If the modems do not train,
3.
troubleshoot the CPE device and the loop as described below under the symptom
"You suspect a problem with the CPE or the subscriber loop." section on page
If the modems train, go to the next step to troubleshoot the port that failed.
4.
To test the modem on the line card, enter dsl test atmslot#/port# self. Results are
displayed automatically after a few seconds. If the modem fails the test, replace the
line card.
Disconnect the local loop and replace it with a test setup that consists of a modem or
1.
CPE that is known to work, and a few thousand feet of wire. If the modems train over
the shorter distance, the problem lies in the local loop or in the CPE. See the steps
that follow. If the modems do not train, the port is probably at fault. Replace the
line card.
Make sure that the CPE at the subscriber site is powered up.
2.
Make sure that the CPE is compatible with the Cisco 6260, and that the software
3.
version running on the CPE is compatible with the software version running on the
Cisco 6260.
4.
Power cycle the CPE. When you turn the power on, the WAN Link LED on the CPE
should blink. If the LED does not blink, check the CPE configuration—if the
interface is shut down, bring it up.
Perform a continuity check to find out if the cabling to the CPE is connected and
5.
intact. For example, if there is a phone on the line, check for a dial tone.
If there is no POTS, check DC resistance by shorting tip and ring at the remote end.
6.
Make sure there are no load coils on the local loop.
7.
Is the local loop too long? The maximum length range is 15,000 to 25,000 feet
8.
(4572 to 7620 meters). Within that range, wire gauge, crosstalk, and multiple bridge
taps reduce the distance over which the modems can train.
Is the local loop too short? DMT modems train best over loops of several thousand
9.
feet. In a test situation with a loop just a few feet in length, the modem might fail to
train. Add wire to the loop.
10.
Replace the CPE.
"You suspect a problem with the CPE or the
5-11.
Cisco 6260 Hardware Installation Guide
FRU-Specific Problems
5-11.
5-11
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