5.3 ISDN BRI and DDR
5.3.3 Step 1 - selecting the ISDN switch type
You must specify the type of ISDN switch used by the service providers at the CO.

Selecting the ISDN Switch Type
Some ISDN service providers use one switch, but emulate the software of another switch. Therefore, the switch type that needs to be configured is the one that has been emulated by the switch, and not the actual brand name of the switch installed at the CO.

When you use the isdn switch-type command in global mode, all ISDN interfaces on the router are configured for the same switch type. If you use the command in the interface configuration mode, only the interface for which you are configuring assumes that switch type.

Following are the global or interface commands that let you specify the ISDN switch located at the CO to which your router will connect:

Router(config)#isdn switch-type switch type
Router(config-if)#isdn switch-type switch type

For BRI ISDN service, the switch type can be one of those listed in the Table.

Depending on the version of Cisco IOS software that you use, you might see different switch types available. If you need to change the specified switch type, you must reboot the router before the different switch-type setting takes effect on the router. To disable the switch on the ISDN interface, specify isdn switch-type.

You can apply an ISDN switch type on a per-interface basis, thus extending the existing global isdn switch-type command to the interface level. This allows BRIs and PRIs to run simultaneously on platforms that support both interface types.

Sequence of Commands for Specifying the ISDN Switch Type
To specify a switch type under your serial interface, you must have configured the E1/T1 controller. But in order to configure the E1/T1 controller, you must have configured the global
isdn switch-type! After the E1/T1 controller is configured—following the configuration of the isdn switch-type—you can introduce the switch command at the interface level. If you wish to, you can also remove it from the global level. The interface isdn switch-type command, if specified, overwrites the isdn switch-type specified at the global level.