Any suggestion for network traffic

I can view all my WAN network in mrtg graphics.I couldn't find which client or clients create maximum bandwith usage.When i have a look mrtg graphics which it shows me maximum bandwith usage and line can disconnect because of created by client or clients maximum bandwith usage(file or folder copying,updates...etc).
Can anybody give me a suggestion to solve this problem by using which network traffic control program.

Thank you.