What’s the other device? I am guessing that there’d be very little “integration” between that device and the G120? If there is a high level of integration, then can you simply expose the functions through one of the devices not both?
Ultimately, yes you will need an actual switch in there - you expose the “uplink” connection to the outside world, and you have the two devices internally connected. I’d look at the device that Architect found.
the other device is another circuit that has MII interface.
The 2 devices can not be integrated at the circuit level, just at the Ethernet level, hence the need for the switch
This makes the need for this type of integration more apparent, but as mentioned before, with the hardware and since you readily admit this is a new area of research for you, integrating your own switch would not be feasible. @ Architect gave a great switch that would work if you, as was also said, buy a larger enclosure, and only expose the WAN or LAN port to the world for external communications, and connect them internally with short Ethernet cables.
Did you consider using a LAN switch dedicated IC based circuit
For example Micrel KSZ8863MLL
This chip provides 3 ports and one of them can be a MII.
@ Rajesh Thanks…looking at that chip
@ James Would this increase the price of the product by alot! Always cheaper to intergrate into one board but i will investigate this suggestion.