I'm using a circuit simulation app called EveryCircuit, and for the npn transistor settings it has forward beta, reverse beta, base resistance, collector resistance, and emitter resistance. I'm a bit confused because I've only heard of alpha gain, beta gain, and voltage drop as parameters of a transistor. I'm assuming that forward and reverse beta are referring to the gain, but I'm not sure why they give settings for the resistance?
Rbe and Rce are useful parameters that are an indication of power handling of the device. My Rule of thumb is Rce = 0.5 / Pmax rated when used as a switch but less relevant when used as a current sink/source. ( CE,CB). Forward beta is usually rated at some current unsaturated then as a switch Vce-sat is rated at Ic/Ib=10 to 50 for superBeta devices >500.
The Rce as Jonk indicated is due to bulk resistance and thus size of semiconductor and thus its thermal resistance and thus max power dissipation improved for this size so Rce is inverse with Pmax, just as it is with all diodes and LED’s with the same correlation of Rs=0.5/Pmax (+/- 50%).
Rce is low as the CB junction has less doping (than BE) and as Vce saturates CB begins to conduct as Vce approaches 0. Then Rce becomes a current controlled conductance which is useful for “linear active loads” or switched loads.
Emitter resistance is usually (Rbe + source Z) / hFE. I think. But will neglect the source impedance just for the transistor characteristic.