September 3, 2009 - 22:49

Many Internet users worry about net neutrality and online privacy these days. And they see deep packet inspection (DPI) as their arch enemy. Common claims are that DPI reads the content of all packets and then decides based on the nature of the content whether to forward, slow down or drop that packet. This is a misconception based on poor understanding how today’s DPI for Internet traffic management works.

DPI is only the core technology of traffic management systems that is used for application classification. This is done by scanning the first few packets — including their payload — of each network flow for certain patterns out of a predefined list. DPI does not ‘read’ or even ‘understand’ any communication content. As soon as the communicating application of a network flow is identified, DPI stops for that flow. Then, bandwidth management rules determine how this flow is treated. Possible rules are:

  • higher or lower priority relative to other traffic
  • bandwidth guarantees
  • bandwidth limits
  • volume caps

In any case, decisions are never made based on content, but based on the application protocol. So if we talk about net neutrality, we need to differentiate between neutrality toward content and neutrality toward application protocols. While content neutrality remains entirely unaffected by DPI bandwidth management, there is indeed an effect on protocol neutrality because in can very well happen that a packet carrying voice data of an Internet telephony session gets preferential treatment over a file sharing packet.

More details about DPI and its impact on net neutrality and online privacy are available in our recently published white paper.


Should companies acknowledge bandwidth management policy to an organization, such as the FCC here in the states? Compaq lost big time trying to play God with content but the consumer lost too and didn’t have a clue what happened. Some DPI companies advertise “control” in ways that lead one to believe their sales are adversely considered without the benefit of ‘fixing’ content.

Robert Mendez (not verified)

[Comcast] (pardon the error) lost big time trying to play God with content but the consumer lost too and didn’t have a clue what happened.

Robert Mendez (not verified)

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