Deep packet inspection could be useful to ISPs who oversell limited bandwidth to (too) many customers. With Deep Packet Inspection, my ISP could inspect the contents and details of the high-bandwith traffic going to and from my neighbor:

Our ISP could then determine most of it to be peer-2-peer traffic, and then limit exactly that peer-2-peer traffic so that my neighbor ( :-) ) doesn’t hog all the bandwidth that we all have to share. On the surface, that sounds like a great idea? Why should my neighbor ruin the internet experience for the rest of us? There’s a catch…

Interestingly, ISPs aren’t going to tell customers exactly what traffic will be limited / throttled, they’ll just go ahead and do it. Today peer-2-peer will be throttled. Tomorrow it’ll be large HTTP downloads and by the way, your ISP might decide that since they also sell their own Voice over IP solution, they’ll throttle Skype so it isn’t usable, and you’ll have to buy their Voice over IP solution. And so on. This is Net Neutrality - we don’t want ISPs selectively throttling certain traffic, because we don’t trust that they’ll have our interests at heart when they do it.

If ISPs do want to do it, they can always do it based on what servers we communicate with. We can’t stop them doing that.

They can also base it on what TCP and UDP ports we use. That is useful, but can be circumvented by using non-standard ports. And some protocols don’t even use standard ports. Deep Packet Inspection would come into play if the ISP wanted to identify even though it was using non-standard ports. They could look at the traffic itself and determine what “it looks like” and base their throttling on that.

And that would work today.

My prediction is, though, that if Deep Packet Inspection were to become common, inevitably people would circumvent that e.g. with encryption. Deep Packet Inspection won’t work on encrypted traffic (because by definition, encrypted traffic can’t be inspected).

So I come to a conclusion:

Deep Packet Inspection leads to Encryption which would also make it impossible for the government to snoop anybody’s emails and have many other benefits. Wonderful. So bring it on!