Monitoring Bandwidth Usage on a Wireless Network

Question

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How can I monitor internet usage in my network?

Is there anyway for me to monitor my network bandwidth without installing firmware on my router? It includes wireless connections and I can't install any programs on the other laptops that use the net. Also, an iPad is used for talking through Skype, I heard that Skype uses a lot of bandwidth and so want to be able to see how much. Is this possible on the iPad? I have a 30GB Bandwidth limit, so I have to see who is using alot of it.

Thanks in Advance,