A method is proposed for operating a mobile radio network, which permits an error-free exchange of packet data units in the event of a connection change between a mobile unit and superordinate network units. In this regard, useful data is transmitted between the mobile unit and a first radio base station, the useful data being combined to form packet data units prior to its transmission. For the transmission of the packet data units, transmission-specific information describing an instantaneous state of the transmission is stored both in the mobile unit and in a first network unit superordinate to the first radio base station. In response to the connection change of the mobile unit from the first radio base station to a second radio base station having a second superordinate network unit, the transmission-specific information stored in the first superordinate network unit is transmitted to the second superordinate network unit to continue the transmission after the connection change essentially directly from its instantaneous state. Prior to the connection change, the transmission of the packet data units from the first radio base station to the mobile unit is halted by the first superordinate network unit. With the transmission-specific information from the first superordinate network unit, a first identifier of the packet-data unit expected as next from the mobile unit in the first superordinate network unit is transmitted to the second superordinate network unit. A first connection-change packet data unit which includes the first identifier is sent by the second superordinate network unit to the mobile unit.