Need help with network traffic analysis

What is the easiest way to ascertain which users on a network may be using large amounts of bandwidth?

I suspect one of the users is having high utilization at times and causing havoc with our VoIP calls. Actually I suspect the issue lies with the ISP but they refuse to acknowledge it. All of the vendors VoIP QoS settings are active in our router and the issue persists. Anyway I'm now down to seeing if it can be pinned on a user at this point.

This is not a domain environment. We have about 40 VoIP Phones, 40 workstations and various mobile devices. The switch is a CISCO SF200. I've gotten PRTG Traffic Grapher running and I've configured the switch to mirror traffic from the port that connects our router to port 48 which is connected to computer running PRTG. I think Im close to getting the info I need but not quite there yet..I guess what Im asking is "Is there a simpler way to be doing this that I'm overlooking?"
BIZNETplusAsked:
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Natty GregIn Theory (IT)Commented:
Capsa is a freeware that will let you know who is eating up your bandwidth.
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*** Hopeleonie ***IT ManagerCommented:
Wireshark is the best software for this.
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RizzleCommented:
We use Wireshark internally to investigate issues like this. Wireshark is particularly good because not only does it tell you the IP from where the traffic is originating but also what application/protocol is associated with the traffic.
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BIZNETplusAuthor Commented:
With wireshark would you still need to set up port mirroring on the switch to see all the traffic?
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RizzleCommented:
Yes that's correct so it can analyse the traffic coming from those ports you specify or if you set all the ports to port mirror.
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*** Hopeleonie ***IT ManagerCommented:
Yes :-)
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Network Analysis

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