You can't communicate to the modem because it is on the WAN side, not the LAN side. The 192.168.1.0 subnet exists only on the LAN side of the router. It will not route to the modem no matter what IP you give it, it will only route to the public gateway on the WAN side.
The only way to talk to the modem itself is to plug it directly into your PC (or LAN side of your router) as make sure you are on the same subnet as it.
The only way to talk to the modem itself is to plug it directly into your PC (or LAN side of your router) as make sure you are on the same subnet as it.