For digital transmission, the Up0-Interface is an integrated services digital network (ISDN) interface used in private networks.
In public networks, the maximum cable length of an U bus is between 4 and 8 km, and the maximum length of an S0-bus is 900 meters for Point-to-Point configuration and about 150-300m for point-to-multipoint configurations.
The Up0-bus has, depending on cable quality, a reach of between 2 and 4 km, far more than the S0-bus.
This allows the use of ISDN telephone equipment in large private networks.
Unlike the S0-bus, the Up0-bus runs at half duplex; that is, both sides alternate in sending and receiving.