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