Garmine Marine Network Wiring

Question

Garmin Marine Network uses an Ethernet like standard for high speed transmission between Ploters, Radar etc. I have tried to connect two GPSMAP 3205 plotters using standard Ethernet RJ45 connection (1) using straightthrough and (2) using a cross over cable. Neither connection works 100% so I suspect Garmin have their own wiring. They sell unterminated cable and connectors but nowhere on the Internet can I find how to connect these items.
Any ideas?