What's the relation between cabin pressure and altitude? Usually, cabin pressure of an airliner is kept at a value corresponding to an altitude of not more than about 2000m. 

Now, I heard that before takeoff, the pressure is already increased a little for higher stability of the fuselage. Maybe, this is wrong, but I had another experience:

I was in a 737-800 flying at 11500m. While the aircraft sank on approach for landing, I felt that typical pressure on my ears several times though we still were above 7000m. So, the cabin pressure already changed at that high altitude. 

So, how is cabin pressure related to outside pressure during the entire flight?
Here is a plot of cabin pressure on one flight. You can see a small increase in pressure right before takeoff. The decrease and increase in pressure is fairly constant during climb and descent. The pressure will change based on the aircraft's altitude, and will not reach a minimum limit until closer to the aircraft's service ceiling. This keeps pressure changes as slow as possible while giving a lower cabin altitude when below the service ceiling.


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