Reverend Red Bull
The DPF actually has two stages contained in one unit. The first stage, the top 1/4 or 1/3 of the DPF unit, is the Diesel Oxidation Catalyst, which works a bit like a catalytic converter, probably the reason for the catalytic converter label sometimes being applied to it. The remaining lower portion of the unit is the actual DPF that traps the soot particles.I could be wrong, but I think the SCR is just an injector in the exhaust stream. The DPF is right off the engine in front of the car and also known as a "catalytic converter" in the parts books.