System information

Troubleshooting ISDN
Book Title
17-382
Port not attached to proper device or
port
Step 1 The ISDN BRI port of a router must be attached to an NT1
2
device.
In ISDN, NT1 is a device that provides the interface between the
customer premises equipment and central office switching
equipment. If the router does not have an internal NT1, obtain and
connect an NT1 to the BRI port. (The Cisco 1004 router has an
internal NT1. An internal NT1 is optional in the Cisco 2524 and
2525 routers.)
Step 2 Make sure that the BRI or terminal adapter is attached to the S/T port
of the NT1.
Layer 1 logic states hung Step 1 Check the status lights on the NT1. For information on interpreting
the status lights, refer to the hardware documentation for the NT1.
Step 2 If the NT1 status lights do not indicate a problem, check the NT1 for
a switch to set the ohm termination. If the switch is present, set it to
100 ohms.
Step 3 Power cycle the NT1.
Step 4 Check the output of the show isdn status privileged exec command.
The command output should say “Layer 1 active.”
Step 5 If the router still does not dial, clear the BRI interface using the clear
interface bri privileged exec command.
Step 6 Again check the output of the show isdn status command to see
whether Layer 1 is active.
Step 7 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 and WAN implementation 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 find out
the correct switch type).
Step 3 Check the cable connecting the BRI or terminal adapter to the telco
jack or NT1. Replace the cable if it is damaged.
Step 4 Make sure the NT1 is functioning correctly. If there is faulty or
malfunctioning hardware, replace as necessary.
Step 5 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 SPID = service profile identifier
2 NT1 = network termination type 1
Possible Problem Solution