There are a few ways you can find the make and model of your gateway:
Look on the front, back, sides, or bottom of your router for the manufacturer name and model.
In the example above, the manufacturer's name is printed in front of the router.
Looking at the bottom reveals that the router is a Netcomm Wireless NF4V.
Netcomm Wireless is the manufacturer, while NF4V is the model.
If it's still not clear, you can search the Internet using identifying items on the router, like the label or name.