David has a good point, this is a rather broad topic.
If I were to make a couple of assumptions, you might be looking at conducted or guided media, meaning wire or fiber optic to a signal from sender to receiver.
In any type of transmission line you will need to know the trade-offs:
* Bandwidth ( hihger BW = Higher data rate)
* Transmission impairments : or impedance that limit the distance
* Interference : (overlapping signals, adjacent channels)
* Number of receivers: loading and distortion, point to point or multipoint
for guided media, you are basically looking at Twisted pairs, Coaxial, microstrip ( PCB), and optical fiber
That's my general answer to this general question
