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 defined number of service classes relating to the quality of service; selecting a service class from said defined number of service classes for the transmission, wherein selecting the selected service class further comprises forwarding a third set of attributes to at least one of the core network node and the access node, wherein the third set of attributes specifies the selected service class, the selected service class determining, by a first unique mapping function performed in the core network node, a first set of attributes, and the selected service class determining, by a second unique mapping function performed in the access node, a second set of attributes; establishing a first transmission context between the core network and the user equipment, wherein the first transmission context is associated with the first set of attributes for defining a first quality of service for an exchange of the data packets with the user equipment in the transmission; and establishing a second transmission context between the access node and the user equipment, wherein the second transmission context is associated with the second set of attributes for defining a second quality of service for the exchange of data packets with the user equipment in the transmission.