1. A control device for specifying a quality of service in a transmission of data packets between a service entity and a user equipment over a mobile network comprising a core network node and an access node which are adapted to control the handling of the data packets sent between the service entity and the user equipment, wherein the control device comprises: at least one microprocessor; a non-transitory computer-readable storage medium, coupled to the at least one microprocessor, containing computer-readable instructions executable by said microprocessor whereby said control device is configured to: receive a set of attributes for a transmission context to be established with the user equipment, wherein the set of attributes encodes a selected service class, wherein the selected service class was selected for the transmission context prior to receipt of the set of attributes and was selected from a plurality of service classes preconfigured in the mobile network, determine the selected service class from the received set of attributes using a unique mapping function, determine a further set of attributes for the selected service class, using the unique mapping function that maps said set of attributes for the determined selected service class to said further set of attributes of a plurality of preconfigured further sets of attributes, and establish the transmission context with the user equipment according to the further set of attributes for defining a quality of service for an exchange of the data packets with the user equipment in the transmission.