The invention relates to an apparatus configured to receive an input message via the first interface. The input message having a first layer structure and containing an information piece associated with the top layer of the first layer structure, extracting the information piece from the input message by passing the input message through a protocol stack associated with the first layer structure from bottom to top, examining the extracted information piece to obtain an examination result, generating an output message by passing the extracted information piece or an information piece generated on the basis of the extracted information piece through a protocol stack associated with a second layer structure from top to bottom, and sending the output message via the second interface. The generating and/or the sending of the output message are performed as a function of the examination result.