in order to transmit data packets in multi - rat networks , a method and a system of network controllers are proposed comprising : simultaneous establishment of radio connections over multiple different radio access technologies or rats , with a user equipment or ue 13 , being one radio connection firstly established over one primary rat under a single pdp context and one or more radio connections established over at least one secondary rat , different from the primary rat , and under the same single pdp context ; simultaneous transmission of data packets over the different rats towards the ue 13 and combination of the transmitted data by higher layer protocols at the ue 13 . in the present method / system , a connection is established for user plane transmission on the same pdp context between a primary network controller 11 of the primary rat and the secondary network controller 12 of a secondary rat . more than one secondary rat may be involved .