1. A method 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 data packets sent between the service entity and the user equipment, the method comprising: pre-configuring a plurality of service classes relating to the quality of service and selecting a service class from said plurality of service classes for the transmission, wherein a first transmission context is established between the core network node and the user equipment, said first transmission context being associated with a first set of attributes for defining a first quality of service for the exchange of the data packets with the user equipment in the transmission, wherein a second transmission context is established between the access node and the user equipment, said second transmission context being associated with a second set of attributes for defining a second quality of service for the exchange of the data packets with the user equipment in the transmission, wherein the selected service class determines the first set of attributes by a first unique mapping function performed in the core network node and the selected service class determines the second set of attributes by a second unique mapping function performed in the access node, and wherein the selected service class is specified by a third set of attributes which is forwarded to at least one of the core network node and the access node, and wherein the first and/or second mapping functions determine the first set of attributes and/or the second set of attributes from the third set of attributes.