A mobile station (110) for use in a Radio Access Network, RAN (102), connected to a core network (101) in which there is one or more Public Land Mobile Networks, PLMNs (103, 104, 105). The mobile station (110) is arranged to select one of said PLMNs (103, 104, 105), and is arranged to communicate with its RAN (102) by means of Radio Link Control, RLC, data blocks. The mobile station is arranged to include the identity, ID, of its selected PLMN in an RLC data block, and to inform the RAN (102) of the presence of the ID of the chosen PLMN in the RLC data block by means of including a reserved or pre-defined value in the length indication field of the RLC data block.