What I think MBDOC means by "braking" traction control system is that the system (ETS) senses slippage during acceleration in one of the wheels and applies the brake to it. This pushes the torque accross to the other wheel through the diff.

ASR adds the extra component of controling the engine power in order to bring the car back under control. You punch the gas and the car says no way buddy I am not letting you have this power so you can run us into the trees! It cuts the power and thats putting it very very simply. Basically I think ASR steps in when you try and overwhelm the ETS by applying more power.

ABS is strictly a brake control system when you are coming to a stop on slippy surfaces.