For digital transmission, the U<sub>p0</sub>-Interface is an integrated services digital network (ISDN) interface used in private networks. It is derived from the U<sub>K0</sub>-Interface used in public networks.
In public networks, the maximum cable length of an U bus is between 4 and 8 km, and the maximum length of an S<sub>0</sub>-bus is 900 meters for Point-to-Point configuration and about 150-300m for point-to-multipoint configurations. The U<sub>p0</sub>-bus has, depending on cable quality, a reach of between 2 and 4 km, far more than the S<sub>0</sub>-bus. This allows the use of ISDN telephone equipment in large private networks. Unlike the S<sub>0</sub>-bus, the U<sub>p0</sub>-bus runs at half duplex; that is, both sides alternate in sending and receiving.
While the S<sub>0</sub>-bus allows for several ISDN device connections (up to 8), the U<sub>p0</sub>-bus can connect only two devices, one at each end of the cable.