confusion on the teacher model

[nikky4D]

What does the teacher model do ? Is the teacher model necessary for dgnet++? it was present in dgnet paper for soft labeling, but it does not appear to be used in dgnet++ paper in adaptation or self-training.

If I need a teacher model, would it then suffice to get a model pretrained on the target domain? and must it only be a resnet50 or would any other type of model work?