A method of operating a mobile radio network for adjusting the counter states of the packet data units to be transmitted in the convergence protocol layer protocol units of network entities of the mobile radio network. User data is transmitted from a first network entity of the mobile radio network, in particular a mobile station, to a second network entity of the mobile radio network, in particular a higher-level network unit, the user data is combined prior to transmission into at least one packet data unit in a first convergence protocol layer protocol unit of the first network entity; and the at least one packet data unit is transmitted from a first radio link control layer protocol unit of the first network entity to a second radio link control layer protocol unit of the second network entity. If the transmission of the at least one packet data unit fails, the first radio link control layer protocol unit transmits an error message to the first convergence protocol layer protocol unit after receiving a confirmation message confirming the failure from the second radio link control layer protocol unit.