How to find our computer network weaknesses?

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I found that not all network have a good performance, in terms of upload and downloading files, sending and receiving mails, using IM, or sometimes, the network filter is not good. I use university network, which is do not allow the user to download movies, but yes if you want to find a hole, there's a hole. I know that the bandwidth of my network is not sufficient to all student inside campus, but I have to proof that. Any body knows, how to proof some weaknesses of our network?