For establishing network connections via a trusted gateway function, a method includes relaying a first set of messages of a first type between a remote unit and a mobile communication network via a non-3GPP access network, sending a connection setup request to the remote unit via the non-3GPP access network, and relaying subsequent messages of the first type between the remote unit and the mobile communication network via the non-3GPP access, where the first set of messages are encapsulated with a first encapsulation protocol and where the first set of messages initiate a registration procedure to the mobile communication network, where the connection request setup contains information for activating a second encapsulation protocol, where the subsequent messages are encapsulated with the second encapsulation protocol, and where the subsequent messages complete the registration procedure.