Information Technology Reference
In-Depth Information
Table 15-7 outlines the possible problems that might cause this symptom and describes solutions to those
problems.
Table15-7 Serial Lines: Increasing Carrier Transitions Count on Serial Link
Possible Problem
Solution
The following
problems can
result in this
symptom:
Check hardware at both ends of the link (attach a breakout
box or a serial analyzer, and test to determine the source of
problems).
1.
If an analyzer or breakout box is incapable of identifying any
external problems, check the router hardware.
2.
Line
interruptions
due to an
external
source (such
as physical
separation of
cabling, red
or yellow T1
alarms, or
lightning
striking
somewhere
along the
network)
Swap faulty equipment, as necessary.
3.
Faulty switch,
DSU, or
router
hardware
Using the show controllers Command
The show controllers exec command is another important diagnostic tool when troubleshooting serial
lines. The command syntax varies, depending on platform:
For serial interfaces on Cisco 7000 series routers, use the show controllers cbus exec command.
For Cisco access products, use the show controllers exec command.
For the AGS, CGS, and MGS, use the show controllers mci exec command.
Figure 15-2 shows the output from the show controllers cbus exec command. This command is used on
Cisco 7000 series routers with the Fast Serial Interface Processor (FSIP) card. Check the command
output to make certain that the cable to the channel service unit/digital service unit (CSU/DSU) is
attached to the proper interface. You can also check the microcode version to see whether it is current.
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