Welcome xmaverick,

Search on 'mrtg' or 'Multi Router Traffic Grapher', it's written in Perl, and produces graphs for daily, weekly, monthly and yearly cumulative data streams using SNMP. I have used it since 1997 and it has never failed (if I did the configs correctly). It can be used on any device that supports SNMP.

Funny, I just this week worked on updating the html output, to give total in/out data streams and total all. (Note: helps if you're paying by the MB like on a smartphone data plan)

You'll find that it's been enhanced and adapted to many other measurements, i.e. emails, spam, etc. I'm not affiliated with the project, just a happy user.

Good Luck