Hmm...
Although it seems like it should be an easy thing to do, it actually isn't.
This is gonna be a long one so pay attention...
The problem is that traffic needs to be separated by protocol and ideally by source and destination ip addresses. This needs good "layer 3" networking gear which a broadband router is not.
1) You enable SNMP on the Netgear router and you install some software that monitors SNMP devices. Basically what happens is that software connects to each SNMP compatible device (most computers and network devices have SNMP) and "polls" it. The device will have a load of info that it will cough out, for example your router might have a value called "TimeConnected" which might be the length of time (often in seconds) that the router has been connected to your ISP. It will probably also have a value for "DataPacketsIn" and "DataPacketsOut" which is a count of the number of packets coming in and out. Chances are it will only have this figure for your net connection, not for each of the 4 switch ports on the back but you might get lucky. The SNMP software will connect to your devices every 5 minutes or so and pull off this count figure and reset it to 0. By doing that it knows how much data came in and out on that port(s) and can thus give you a running total for the day, week or month and even draw you a graph. This is how we bill for server usage at work, we poll the switch and it tells us how much traffic went in and out of that servers switch port. If your router does not report the info for the 4 internal switch ports (and chances are it does not) you will need to buy a switch that does and stick it between your router and your NAS box.
Alternatively your NAS box may respond to SNMP and give the figure to your software.
2) Even if you get the system above working, either by monitoring the switch port the NAS box is connected to or by getting the info off the NAS box, the problem is, how much of that traffic to the NAS box was to/from the internet and how much was you accessing it yourself on the local network right? The switch port doesn't know, it just counts packets as they pass... This is the problem we had/have at work. Customers with 2 servers might have a situation with their servers are communicating with each other and something as simple as them sending a file from one to the other that's say 1GB in size will get counted twice, once on the port of the source server and once on the switch port of the destination server. Oops!
So we now use something called Netflow on our Cisco routers to not only look at how much traffic came from a certain place, but where it was going to and what typer of traffic was it (eg FTP, Web etc). But clearly you're not gonna buy a 30 grand router right?
But your only option really is to use SNMP to monitor the traffic to the switch port that the NAS box is on but you will have to remember to bear in mind that some of that access will be you. Hopefully you will know which access is you as on the graph that your SNMP software will give you any traffic that is faster than your internet connection can do is clearly you on the local LAN. Plus it won't break it down per user for you.
Bearing those limitations in mind you will need to install something like MRTG on your Mac which will run through the Macs built-in web browser. To do so it will also need you to install MySQL and possible PHP. Installing PHP and MySQL is fairly straightforward but MRTG is not as easy as it could be. And then you will need to download a MIB for each device you want to monitor (which is a config file that details the SNMP communication details for that device) and add it to MRTG.
Seriously, it's not simple unless you're a techie but it is the way it's done at most small ISP's / hosting companies...
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There is no app you can just download, install and get what you want virtually automatically.
The closest to it is this:
http://dartware.com/downloads/index.html?sfx=fiveforfree&src=fiveforfreeIt's called Intermapper and it runs on OSX. I used it for a while to monitor the traffic on my home network but stopped after I had difficulty getting it to work with my bizarre router (would have been easier with a Netgear). It gave me basic info but not the live transfer speeds (although it can with some routers). It's very cool but you will still need to faff with it. It's by far a lot easier to use than MRTG believe me... It can use SNMP to pull off stats from devices, but getting the "probe" configured just right for each device can be tricky and it can only pull off what information the device offers up. So if your router or NAS box wont tell it what it needs to give you the usage graphs you'll need to buy what is called a "fully managed" switch to sit between your router and the rest of your stuff and monitor that. Bear in mind they start at a good £150 I would have thought, just for a 10/100 version with a small amount of ports.
