CST - Discrete port or Waveguide port?

Hello everyone.

I'm learning CST Studio SuiteCST Studio Suite 

I'm trying to simulate a microstrip line TDR (characteristic impedance) in CST Learning Edition.

In this case, I have two choices, discrete port or waveguide port.

However, I'm not sure which I should use.

So, could you give me some advice?

waveguide port