To reply exactly I have to know another little thing: does the Time Capsule give out its own IP range or passes the DHCP to the Rogers modem? Basically: what is the IP of the Time Capsule with respect to the Rogers modem (10.x.x.x? 172.[16-31].x.x? 192.168.x.x? Something else?) Your computer, behind the TC has the same class of IP or something else? If you don’t mind write them.
In this case it could also be necessary that you change the DNS of the Rogers modem, but I’m not 100% sure until you give me those details.
The domain refers to the hostnames of the local LAN, basically a sort of Dynamic DNS for each device that is available locally. You could theoretically put everything you want in there, if you then accessed an hostname that is in use (assume you computer is called jonathan, the full hostname would be jonathan.pub.net.cable.rogers.com) through a browser it should resolve to the local IP of your computer. Usually it is not used a real, active, domain (at least that you don’t control) because if for some reason one of the local hostnames becomes used on the public internet you wouldn’t be able to access the remote one without network changes (basically the same thing that CF is now experiencing with 18.104.22.168 that some ISPs and LANs used it as a bogus address meaning many people aren’t able to access it, only translated to hostnames and domains).