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Troubleshooting steps/commands for Voice ports







This document mentions about the commands used for troubleshooting voice ports.After physically connecting analog or digital devices to a Cisco voice-enabled router, you might need to issue show, test, or debug  commands to verify or troubleshoot your configuration.


Troubleshooting steps


Six steps to monitor and troubleshoot voice ports:



1.     Pick up the handset of an attached telephony device and check for a dial tone. If there is no dial tone, check the following:-



  •      Is the plug firmly seated?
  •      Is the voice port enabled?
  •      Is the voice port recognized by the Cisco IOS?
  •      Is the router running the correct version of Cisco IOS in order to recognize the module?




2. If you have a dial tone, check for DTMF voice band tones, such as touch-tone detection. If the dial tone stops when you dial a digit, the voice     port is probably configured properly.


3. Use the show voice port command to verify that the data configured is correct. If you have trouble connecting a call and you suspect that the         problem is associated with voice port configuration, you can try to resolve the problem by performing Steps 4 through 6.



4. Use the show voice port command to make sure that the port is enabled. If the port is administratively down, use the no shutdown command.



5. If the port was working previously and is not working now, it is possible that the port is in a hung state. Use the shutdown/no shutdown command sequence to reinitialize the port.If you have configured E&M interfaces, make sure that the values associated with your specific PBX  setup are correct. Specifically, check for two-wire or four-wire wink-start, immediate-start, or delay -start signaling types, and the E&M interface type.These parameters need to match those set on the PBX for the interface to communicate properly.


6. You must confirm that the voice network module (VNM) (that is, the module in the router that contains the voice ports) is correctly installed.With the device powered down, remove the VNM and reinsert it to verify the installation. If the device has other slots available, try inserting the VNM into another slot to isolate the problem. Similarly, you must move the voice interface card (VIC) to another VIC slot to determine if the problem is with the VIC card or with the module slot.


Six show commands for verifying the voice port configuration:-



Commands to Verify Voice Ports



show voice port

Shows all voice port configurations in detail

.show voice port slot/subunit/port

Shows one voice port configuration in detail

show voice port summary

Shows all voice port configurations in brief

show voice busyout

Shows all ports configured as busyout

show voice dsp

Shows status of all DSPs

show controller T1 | E1

Shows the operational status of a controller


Below table provides a series of commands used to test Cisco voice ports. The test commands provide the ability to analyze and troubleshoot voice ports on voice-enabled routers. There are five test commands to force voice ports into specific states to test the voice port configuration. The csim start dial-string command simulates a call to any end station for testing purposes.




test voice portport_or_DS0-group_identifier




m-lead | battery-reversal | ring | tip-ground | ring-ground | ring-trip

} {

on | off | disable


Forces a detector into specific states for testing.

test voice portport_or_DS0-group_identifier




local | network

} {

1000hz | 2000hz | 200hz | 3000hz | 300hz | 3200hz | 3400hz | 500hz | quiet | disable


Injects a test tone into a voice port. A call must be established on the voice port under test. When you are finished testing, be sure to enter the


command to end the test tone.

test voice portport_or_DS0-group_identifier




local | network | disable


Performs loopback testing on a voice port. A call must be established on the voice port under test. When you finish the loopback testing, be sure to enter the


command to end the forced loopback.

test voice portport_or_DS0-group_identifier




e-lead | loop | ring-ground | battery-reversal | power-denial | ring | tip-ground

} {

on | off | disable


Tests relay-related functions on a voice port.

test voice portport_or_DS0-group_identifier




fax | disable


Forces a voice port into fax or voice mode for testing. If the voice port does not detect fax data, the voice port remains in fax mode for 30 seconds and then reverts automatically to voice mode. After you enter the

test voice port switch fax

command, you can use the

show voice call

command to check whether the voice port is able to operate in fax mode.

csim start



Simulates a call to the specified dial string. It is most useful when testing dial plans.



ISDN show and debug commands specific to the monitoring and troubleshooting of ISDN connections:-



show isdn active                                   

Shows ISDN calls in progress

show isdn history         

Shows ISDN call history

show isdn status   

Shows ISDN line status

show isdn timers                                    

Shows ISDN timer values

debug isdn events                                  

Displays ISDN events in real time

debug isdn q921 Displays ISDN Q.921 packets in real time
debug isdn q931                                       

Displays ISDN Q.931 packets in real time



Hex ValueCauseExplaination


Unallocated (unassigned

The ISDN number was sent to the switch in the correct format; however, the number is not assigned to any destination equipment.


Normal call clearing

Normal call clearing has occurred.


User busy

The called system acknowledges the connection request but is incapable of accepting the call because all B channels are in use.


No user responding

The connection cannot be completed because the destination does not respond to the call.


No answer from user

(user alerted)

The destination responds to the connection request but fails to complete the connection within the prescribed time. The problem is at the remote end of the connection.


Invalid number format

The connection could not be established because the destination address was presented in an unrecognizable format or because the destination address was incomplete.


Normal, unspecified

This reports the occurrence of a normal event when no standard cause applies. No action is required.


No circuit/channel available

The connection cannot be established because no appropriate channel is available to take the call.


Network out of order

The destination cannot be reached because the network is not functioning correctly, and the condition might last for an extended period of time. An immediate reconnect attempt will probably be unsuccessful.


Requested circuit/channel not available

The remote equipment cannot provide the requested channel for an unknown reason. This might be a temporary problem.


Requested facility not subscribed

The remote equipment supports the requested supplementary service by subscription only. This is frequently a reference to long-distance service.


Bearer capability not authorized

The user requested a bearer capability that the network provides, but the user is not authorized to use it. This might be a subscription problem.


Incompatible destination

This indicates that an attempt was made to connect to non-ISDN equipment—for example, to an analog line.


Mandatory information element missing

The receiving equipment received a message that did not include one of the mandatory information elements. This is usually the result of a D-channel error. If this error occurs systematically, report it to your ISDN service provider.


Invalid information element contents

The remote equipment received a message that includes invalid information in the information element. This is usually the result of a D-channel error.

95Call Rejected


The destination is capable of accepting the call, but it rejected the call for an unknown reason.




Related Links

Using the show isdn status Command for BRI Troubleshooting [ISDN, CAS]

Designing and Deploying VoIP over ISDN