What's the difference between propagation delay and transmission delay?
Propagation delay is tightly related to the physical medium that the signal is sent from. It might be an optic fiber, coaxial cable or a twisted pair copper wire.
Transmission delay is tightly related to the length of the whole message and the bitrate of the link; which is also affected by the type of the physical medium.
Though it might be completely two different things at the first glance, they might affect each other. Because the actual bitrate of the medium is also dedicated to the type of the physical medium.