In a Standby configuration, one of the ISDN Controllers of SX2 DualPRI V2 is configured in TE mode, the other one in NT mode. The ISDN controller in NT mode must be configured in a way that in the card driver configuration on the „ISDN Parameters" tab the option „Obtain clocking from other board connected via PCM bus" is activated (can be activated in NT mode only!). This ensures that the ISDN controller is synchronous to the ISDN controller in TE mode.