When you configure the T1 controller, two corresponding D- channel serial interfaces are instantly created. You must configure each serial interface to receive incoming and send outgoing modem signaling. Note The ISDN switch type should match the telco switch type. Configure the switch type using the isdn switch-type global configuration command. In North America, the options are NI1, 5ESS, and DMS 100.
Options are more varied in other countries.
Because some telcos charge more for ISDN data calls, you might want to configure the isdn incoming-voice data command to process ISDN calls as voice calls, which provides you with data service at a voice billing rate. However, incoming modem calls will not be passed to the modems with this command enabled. Native ISDN calls are directed like a protocol. The dialer interface serves as the parent interface that contains additional protocol characteristics. The ISDN dialer interface is the parent interface that holds the central protocol characteristics for the two ISDN D channels that are part of dialer rotary-group 1.