Sustain pedal midi data? is it just on/off

[dentaku]

I'm wondering if a sustain pedal plugged into the sustain port of an MPK49 (or any midi controller for that matter) sends 0-128 like a knob or does it only send an on/off signal.

Software like Alicia's Keys supports "half pedaling" so I'm assuming a good sustain pedal MUST be more than just an on/off switch.

Can some who own a sustain pedal test this out for me?
If you map your sustain pedal to a knob in Ableton Live, for example, can you control it just like you would with a knob on your MPK49 or the modwheel?