This circuit is equivalent to small-signal common source JFET amplifier:
If you look at the input and output impedance you can see that Zin = R1 || R2 and Zout = rd || Rd || Rl. It can be seen from the small-signal model.
But shouldn't small-signal model look like this?
I just want to understand these models and maybe derivate input and output impedance myself.