Adaptation layer for realising protocol adaptations in a digital wireless data transmission system

In order to perform data transmission between a mobile station and a cellular radio network, the cellular radio network comprises a radio access network (104, 105, 106) for processing messages according to a first protocol, and a core network (101, 102, 103) for processing messages according to a second protocol. The mobile station deals with messages according to the first protocol on given lower protocol layer. On an adaptation layer (301) located between the higher protocol layer and the lower protocol layers, there is performed an adaptation where the messages according to the first and second protocol are mapped into each other.