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| 4.4 |  | Troubleshooting ISDN |
| 4.4.2 |  | Troubleshooting ISDN primary rate switch types |

In order to communicate correctly a router must be told what type of ISDN switching equipment is used by the telco. Depending on the combination of telco equipment and the ISDN switch type configuration, a variety of symptoms are possible. It is usually quickest to simply make a careful check using the show running-config command and verify that isdn switch-type and pri-group timeslots are configured correctly. To specify the central office switch type on the ISDN interface, use the isdn switch-type global configuration command. Options for this command include:

- primary-5ess
- primary-dms100
- primary-ni

Contact the Service Provider for the correct values to use.

To configure the isdn switch-type and pri-group:

> Router#configure terminal
> Router(config)#isdn switch-type primary-5ess
> Router(config)#controller t1 0
> Router(config-controller)#pri-group timeslots 1-24