My recommendation was to monitor the bandwidth only every few minutes. With the upcoming version 7.1 of PRTG Network monitor we have added a new feature that makes measuring available bandwidths fairly easy. The HTTP Advanced sensor now has a new channel which shows the bandwidth in Kbit/s that was achieved while downloading a file from an HTTP URL. Now you only have to set up such a sensor, choose a URL with a medium sized file (e.g. 500 kb or 1 MB) on a server that is "close to your dataline" in a network topological perspective (i.e. very few hops between you and the server) and let it run for some time. Note: Remember that - if you download a 1 MB file every 5 minutes from a public server - you will create bandwidths costs of about 8 Gigabytes per month for the owner of the server and eventually for your dataline. So use your own server! This screenshot shows how we monitor the speed of a dataline by downloading a 1 MB file every 5 minutes. You can see that the bandwidth seems to be degraded every evening between 20:00 and 23:00 hours.