Can two walk together, except they be agreed? [Amos 3:3]

  
A well articulated video from Tekelec's Chief Marketing Officer Susie Kim Riley explaining the difference between DPI and policy control.

While this may look like a trivial issue, I've seen many people get confused on this subject. Sometimes the confusion results from the way policy management vendors present and name their solutions or products (e.g. "Bandwidth on Demand Application Manager" , "Tiered Service Controls") as this may be interpreted as controlling the traffic [i.e. PCEF/DPI side] rather than being the management side. Maybe the term "policy management" is better than "policy control".

Nevertheless, as Susan says" "DPI and policy control are in many instances used hand-to-hand"

See also "PCRF - DPI Compatibility Matrix" - here.