ZDnet on DPI

Michael Kassner at ZDnet wrote a pretty good introductory text about what DPI will mean to end users, from an end user perspective. Most of it is pretty much spot on and it's a good read. Some notes about the parts that aren't:

"Enforcement of service-level agreements: ISPs can use DPI to ensure that their acceptable-use policy is enforced. For example, DPI can locate illegal content or abnormal bandwidth usage."

"DRM enforcement: DPI has the ability to filter traffic to remove copyrighted material. There's immense pressure from the music and film industries to make ISPs responsible for curtailing illegal distribution of copyrighted material."

DPI gear is, by itself, actually pretty bad at discoverying illegal content. For decent gear it's somewhat easy to spot encrypted P2P, it's easy to spot Freenet, I2P, tor, etc - but it's not very easy to ascertain that the content being transferred is illegal. For the P2P traffic, you'd gain more information by asking the P2P network itself (it's still a mammoth task though). Freenet and I2P are designed to make this pretty hard, since - unlike normal file-sharing P2P networks - there's no authorative list of which IP is offering what data.

Granted, it's perfectly possible to say that P2P should be blocked, period, and this is something stream identification + traffic filtering can do for you. Quite a few places do this, especially higher education sites.

Spotting 'abnormal bandwidth usage' doesn't necessarily require DPI. You could spot this on a per-subscriber basis without any DPI gear what so ever. Traffic shaping equipment usually makes this a trivial exercise and provide stream identification at the same time, though.