For Berlin, tariff areas are defined and divided into tariff zone A, B, and C. Tariff zone A covers Berlin's inner city up to and including the urban rail ring. Tariff zone B covers the area outside the urban rail ring up to the city boundary. Whereas tariff zone C includes Greater Berlin (area approx. 15 km around the State of Berlin), including the City of Potsdam. Mobile tickets are available for the tariff zones AB, BC and ABC.