What ISPs need to implement is a simple system for tapering bandwidth, based only on number of bits transferred in a given time period.

An ISP / Broadband provider has a fixed total bandwidth which they divvy out amongst the customers - most people the net for less than 30 minutes a day, and are clicking a link every few minutes.

The `problem' is that a fraction of people really do try to download at full bandwidth 24/7 with automated tools, which the infrastructure can't support.

so: Make a system with a rolling time window in which the first 5Gb downloads at full speed, then the next 2.5Gb at half speed, then the next 1.25Gb at quarter, etc. so you run into a soft barrier and can never exceed 10GB per week or whatever is actually sustainable for them as a service provider, rather than you download 100GB at full whack and then get your service abruptly terminated.

You can implement that system with a couple of kilobytes of data per customer, eg. downloaded bits/hour over the last month. As a customer, you can't work round it.

The problem with filtering based on protocol is a) it's more technically involved, so you'll need specialist hardware to do it fast enough, and b) it will make an incentive to for the protocols you target to disguise themselves, so c) your investment in filtering technology risks being obsoleted, and d) you'll be in a worse position compared to a competitor who opted for a simple rationing scheme, and invested the extra cash in providing more capacity with cheaper hardware.