|I'm not sure of your level of experience, but MRTG is typically best suited for something like this. It's open source, reports bandwidth utilization by interface and historically logs the information for you so you can trend and plan for growth or consolidation. It's extremely popular in the network realm of monitoring tools. |
Unfortunately, as i understand it, your device does NOT do NetFlow which is a shame as there are also some free Windows and Linux tools available which would sort your bandwidth utilization into fields such as Source, Destination, port information, traffic information e.g. http, ftp etc....
Until NetFlow is supported, MRTG would give you what you're looking for here.
If can be found at the following location: http://oss.oetiker.ch/mrtg/