Difference between Throughput and propagation speed.?

Answer 1

If you're comparing throughput and propagation speed, I assume the question is specific to wiring/cabling. Throughput is essentially the number of bits per second through a cable, like 100 Mbps or 1 Gbps, etc. This is a function of the transmission equipment, like the network interface card, and has nothing to do with the actual wire or fiber or atmosphere used to communicate.

Propagation speed is the speed at which the signal travels down the wire or through the air. This is often said to be the speed of light, 3x10^8 meters/sec, but that's not really true. There is the NVP, nominal velocity of propagation to consider. Basically, the signal is not traveling in a vacuum like radio waves through outer space, but down a copper wire or glass fiber or through the atmosphere, and travels at more like 60% to 80% the speed of light. Exactly how fast the signal travels down the wire/fiber depends on the dielectric constant of the material, lower dielectric constant means faster signal propagation.