The SDM family can connect to an ISDN exchange via an EXLIC card that supports 8 basic rate U-interfaces with the 2B1Q code.

The SDM family can connect to NT1's via a SULIS card that has 8 basic rate U-interfaces with the same 2B1Q code.

ISDN terminals connect to the NT1's

The ISDN exchange and the NT1's are connected to the SDM via a wire pair of up to 8Km (0.6mm wire) called the U-interface. The U-interface offers full duplex data transmission via two B-channels and signalling on the D-channel. The SULIS provides remote powering to the NT1's.

With EXLIC and SULIS units the U-interface can be prolonged and ISDN services can be provided to remotely sited subscribers via access networks of SDM's.