I believe DSL modems don't offer any kind of monitoring of data and traffic. If nothing is listed in the user manual, I recommend that you bridge the modem and connect a external router that has better traffic monitoring features. Some routers have some traffic monitoring features and control features.
D-Link routers have control features however only provide a overall traffic data monitoring or live usage reports with out having any kind of controls over it. Netgear routers have more advanced monitoring controls and traffic data features that you may want to check out. I don't know if ASUS routers have similar features. Something you may have to review each router MFr and see what would work best for you.