A fire alarm network fiber optic multiplex modem includes plural local interfaces, a fiber optic interface, a multiplexor, a fiber optic modem, and a demultiplexor. A secure registration request message containing an encryption technique and public key is sent from an originating gateway 105 over a packet data network 100 to a terminating gateway 105. The mechanisms may include combining and aggregating areas of layers to create one opaque surface, aggregating non-overlapping semi-transparent opaque areas of layers, or creating surfaces from overlapping semi-transparent surfaces. Right and left reinforcing plates are provided in a hollow space of the crossmember at portions at which the extension members are joined to the crossmember.