They should have a list of compatible modems. However since it provides your phone, I suggest you install a WAP instead. Google "How to use a router as a WAP" to see how I do that on the cheap.
My cable modem is not a rental here. But it's because it provides the phone service so no rental fee. Different companies, different plans.
My parents rent a Xfinity DOC SIS 3.0 Cable Modem SMCD3GNV. This wireless gateway is just awful. It's WiFi range is poor and the fact that it is a rental is just bad.
I am seeking advice on how I should find replacement hardware. I have no experience in the voice part of the network because I don't use LAN lines.
Their ISP is Xfinity and they are using internet over coaxial cable.
Thanks for taking the time to read my post.