We all live with those little "glitches" in our home networks. Was one of the kids hitting Netflix, did my music downloads go into overdrive, or did my ISP decide to do a remote reboot of my DSL/cable modem? It's certainly true that monitoring networking equipment can be a rather involved process, but every once in a while we stumble across something that makes it fairly easy for the typical home user.
Fluke Networks, a vendor of network analysis and troubleshooting equipment, offers quite a bit of educational material in exchange for the typical contact information. As I was checking out their various goodies, I stumbled across their "Switch Port Monitor." Now, it was designed for use in a LAN environment with enterprise-class switches, but it uses standard Simple Network Management Protocol (SNMP). This means that SPM should also work fairly well with many typical pieces of ISP home equipment. I pointed SPM at my DSL modem, let it gather a bit of data, and presto! I was looking at a nice, clean, 10-second-update bandwidth report.
If your DSL/cable modem talks SNMP--and most of them do--this is worth the download. You'll have to do a bit of research to understand (and differentiate among) the various interfaces on your device, but this one is well worth the effort.