Ed Felten on Network Discrimination

Ed Felten is writing an excellent series of series of blog entries on network discrimination (Part 1, Part 2, Part 3), focusing on the nuts and bolts of how Internet Service Providers can (and do) discriminate between network traffic they like for various reasons (commercial, legal, etc.), and network traffic they do not like. Today’s entry focuses on encryption. Felten points out something that had never occurred to me: even if the user encrypts network traffic so that the ISP can’t see what he’s doing (or even tell the traffic in question apart from the standard website traffic), the ISP can still implement methods that selectively prefer certain types of traffic over others:

But the ISP may have a different and more effective strategy. If the ISP wants to hamper a particular application, and there is a way to manipulate the user’s traffic that affects that application much more than it does other applications, then the ISP has a way to punish the targeted application. Recall my previous discussion of how VoIP is especially sensitive to jitter (unpredictable changes in delay), but most other applications can tolerate jitter without much trouble. If the ISP imposes jitter on all of the user.s packets, the result will be a big problem for VoIP apps, but not much impact on other apps.

So it turns out that even using a VPN, and encrypting everything in sight, isn’t necessarily enough to shield a user from network discrimination. Discrimination can work in subtle ways.