5.5 ISDN Configuration Tasks
5.5.3 Writing the IOS commands to define an ISDN switch type
Before using ISDN BRI, you must define the ISDN switch-type global command to specify the CO switch to which the router connects. The Cisco IOS command output shown in the figure helps illustrate the supported BRI switch types (in North America, the most common types are 5ESS, DMS100, and NI-1). To configure a CO switch on the ISDN interface, use the isdn switch-type command in global configuration command mode. The full syntax of the command is:

isdn switch-type switch-type

The argument switch-type  indicates the service provider switch type. switch-type  defaults to none, which disables the switch on the ISDN interface. To disable the switch on the ISDN interface, specify isdn switch-type none.

The following example configures the AT&T 5ESS switch type:

isdn switch-type basic-5ess

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