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 (“MCN”) via a non-3GPP access, sending a connection setup request to the remote unit via the non-3GPP AN, and relaying subsequent messages of the first type between the remote unit and the MCN via the non-3GPP access, wherein the first set of messages are encapsulated with a first encapsulation protocol and wherein the first set of messages initiate a registration procedure to the MCN, wherein the connection request setup contains information for activating a second encapsulation protocol, wherein the subsequent messages are encapsulated with the second encapsulation protocol, and wherein the subsequent messages complete the registration procedure.