System information

Troubleshooting ISDN Connections 17-385
ISDN: Dial Does Not Go Through PRI
Incorrect cable Step 1 Make sure you using a straight-through DB-15 cable.
Step 2 If you are using any other cable, replace it with a straight-through
DB-15 cable.
Port not attached to proper device or
port
The ISDN PRI port of a router must be attached to a CSU device. If the port is
not connected to a CSU, obtain a CSU and attach the PRI port to it.
Layer 1 logic states hung Step 1 Check the status lights of the CSU. For information on interpreting
the status lights, refer to your vendor documentation.
Step 2 If the CSU status lights do not indicate a problem, power cycle the
CSU.
Step 3 Check the output of the show isdn status privileged exec command.
The command output should say “Layer 1 active.”
Step 4 If the router still does not dial, clear the PRI interface using the clear
interface serial privileged exec command.
Step 5 Again check the output of the show isdn status command to see
whether Layer 1 is active.
Step 6 If Layer 1 is not active, contact your carrier to confirm the
connection.
Media problem For information on troubleshooting WAN media, refer to the appropriate
chapter for your media elsewhere in this book.
Hardware problem Step 1 Use the show isdn status privileged exec command. The output of
this command should indicate “Layer 1 active.”
Step 2 If the output does not say “Layer 1 active,” verify that the configured
switch type is correct (check with your service provider to determine
the switch type).
Step 3 Check the cable connecting the PRI to the CSU. Replace the cable if
it is damaged.
Step 4 Make sure that the router is functioning correctly. If there is faulty or
malfunctioning hardware, replace as necessary. For more
information, refer to Chapter 3, “Troubleshooting Hardware and
Booting Problems.”
1 MIP = MultiChannel Interface Processor
2 CSU = channel service unit
Possible Problem Solution