What are the signal losses and their amplifications in the network components like routers, bridges, etc?

Answer 1

Not sure I understand exactly what the question is... The routers and bridges and switches do not amplify the signal, but regenerate it on the outgoing interface. The signal loss is a function of distance between the two devices passing the signals back and forth. The components themselves do not attentuate the signals any further once they are detected on the input side of whatever device they are entering. The signals enter, and frames/packets are switched/routed, and the signals are then regenerateed when the frames/packets are sent back out on the wire, at a set voltage.