The image on the left is just one of the graphs generated automatically for tracking the data usage on my home network.
That particular graph shows the usage of my ADSL connection over time; green is downloaded data, while the blue line shows my uploads. It is generated by Tobi Oetiker’s outstanding MRTG – The Multi Router Traffic Grapher. MRTG is a free Perl script that connects to any device capable of talking SNMP and pulls interesting data from it.
I currently log DSL, Wireless and LAN use (Bytes per second), along with line noise and Noise Margin of the DSL connection. I could also log what the switch in my network is doing, and even what my various servers are up to. As you can see from the graphs you get a nice indication of traffic patterns over time – it’s very easy to spot peaks when BitTorrent kicks in and out, or when someone in a different time zone is playing on my Counter Strike server!
It gives me an “at a glance” overview of what most of my networked devices are doing – which was enough to make me notice the other day that despite having all my wireless devices switched off, something was still polling the Access Point. Turns out I’d left one of the laptops disassociated – but on – and it was sending a little chatter to the AP every few hours.