|Some routers have the capability to log bandwidth/packet use/transport. I once setup a Linux-based router on an old PC, and it had an amazing amount of capabilities/features. If your modem/router doesn't have these features, you could be out of luck.|
It may be that software exists that navigates the network to retrieve the information from each PC. Of course the data would need to be logged on each machine, first. I'm not aware of any client/server-type software for this purpose, but it may exists.
Try Googling "network monitoring software".
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