Here's a related project http://oss.oetiker.ch/rrdtool/ follow the tutorial you might learn from it.

Is this your university project?

If so I'd suggest you look up Cacti it's an open source project that maybe useful to you.  I'm not a programmer but I use Cacti for my Corporate  customers here in the UK and it's a great tool for bandwidth graphing.

http://www.cacti.net/

I don't know how you can implement it for the project at hand but I'm sure it will be a useful resource to start with.

Good luck.